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How to Do Cool Science Experiments With Rubbing Alcohol and Baking Soda

Science Projects with Dishwashing Liquid

With some ordinary rubbing alcohol, baking soda and a few other household odds and ends, you can do some pretty cool science with your kids or your students. Make a snake, clean your coins and play with your food. These experiments are instructive, of course, but they're also fun.

Soda Snake Experiment

Place a small mound of sand on a heat-proof surface.

Press your finger into the top of the mound to create an indentation large enough to hold half a golf ball.

Pour 5 teaspoons of rubbing alcohol into the dent.

Gently mix 1 teaspoon of baking soda with 4 teaspoons of sugar in a separate bowl. Pour the mixture into the dent on top of the rubbing alcohol. Stir the mixture gently without making the mound collapse.

Light the mound with a match by touching the flame to the mixture at the top of the mound. A "snake" will start to grow from the mound.

Marshmallow Experiment

Mix rubbing alcohol and baking soda in a small bowl. Add a marshmallow to the bowl. Have the students record what they see happening to the marshmallow in their journals after a few minutes.

Repeat Step 1, but this time soak one marshmallow in rubbing alcohol and another in baking soda. Ask the students to note in their journals what happens after a few minutes.

Combine rubbing alcohol and baking soda with other substances, such as vinegar, and keep repeating the experiment. Ask the students about their observations afterward, and discuss why the marshmallows reacted differently with different substances.

Dirty Penny Experiment

Add 1 tablespoon of baking soda to one bowl, 1 tablespoon of baking soda to another bowl, and 1 tablespoon of some other substances, such as vegetable oil, vinegar, lemon juice or dish soap, to some other bowls. Put just one substance in each bowl.

Submerge a dirty penny in each bowl for 24 hours.

Rinse each penny with water.

Have the students record in a journal which substances did the best job at cleaning the pennies, and discuss why that is the case.

Things You'll Need

Related articles, how to make rock candy at school, how to build a solar system model for kids, pollination activities for kids, chalk and vinegar science projects, experiments on cleaning pennies, density experiments for kids, chemical reaction experiments for middle school students, how to make a rubber ball out of an egg, fun science experiments for adults, food coloring experiments, school projects with magnets, easy science projects for kindergarten, how to drop an egg without breaking it by using straws..., magic science tricks for kids, how to make a volcano for kids using mud, kids' science projects on things that melt, how to blow up a balloon with vinegar and baking soda..., natural disaster project ideas.

• Toad Haven: Peep Science
• Science Museum: Soda Snake Fireworks
• Finishing.com; Substances for Cleaning Pennies; Ted Mooney

About the Author

Based in the Washington, D.C., area, Dan Taylor has been a professional journalist since 2004. He has been published in the "Baltimore Sun" and "The Washington Times." He started as a reporter for a newspaper in southwest Virginia and now writes for "Inside the Navy." He holds a Bachelor of Arts in government with a journalism track from Patrick Henry College.

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Science Fun

Cloud In A Bottle

Learn how to make a cloud in a bottle with this super simple and really cool weather science experiment.

• Empty plastic water bottle with cap
• Isopropyl rubbing alcohol
• Safety goggles

Instructions:

• Use the scissors to carefully remove the label from the plastic water bottle.
• Put on your safety goggles.
• Pour a small amount of alcohol into the bottle.
• Put the cap on the bottle. 
• Slowly rotate the bottle so the alcohol coats the inside of the bottle.
• Grab the bottom one third of the bottle and twist. This will create pressure in the bottle.
• Release and watch your Cloud In A Bottle form right before your eyes.

WATCH THE QUICK VIDEO TUTORIAL

How it Works:

The pressure you created inside the bottle forced the water vapor to compress together, heat up, and evaporate into gas. When you released the pressure, the water vapor molecules cooled quickly and condensed to form a visible Cloud In A Bottle. 

Make This A Science Project:

Try the Cloud In A Bottle demonstration is areas that are significantly colder or hotter and record any noticeable differences. 

EXPLORE TONS OF FUN AND EASY SCIENCE EXPERIMENTS!

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Science Experiment for Kids: Seeing Your DNA

When people think of DNA they usually visualize the elegant “twisted ladder” shape seen in everything from advertising logos to Biology textbooks. This visual is actually a kind of artist’s conception. It is a kind of scientific model, useful in helping us understand how DNA functions, but in reality impossible to see.

The structure of a molecule is far too small to be seen with even the most powerful of microscopes. Rosalind Franklin used the process of X-ray crystallography to make an image of the DNA molecule that was used by Watson and Crick to build that first model; but X-ray crystallography is a bit complex for most students to do at home.

Still, some of you might want to do something a bit more dramatic than building a DNA model out of toothpicks and gumdrops. You might not be able to actually see little A,C,T and G pieces, or even a single DNA strand, but did you know that you can use some common kitchen ingredients to extract DNA from your own cells — DNA that you CAN see? First, read this related article: DNA: Definition, Structure & Discovery .

What You Need:

• Small paper cups (You want the smallest sized cups.)
• 1 bottle of colorless sports drink (You can also use a strong salt water solution, but “Lemon Ice” flavored Gatorade tastes better — and you can use the leftovers for refreshments after the lab!)
• Liquid dish soap (You want to use the lightest color or colorless brand you can find)
• A few drops of pineapple juice (You could also try using a quarter-teaspoon of meat tenderizer dissolved in a half-cup of water)
• 1 wood skewer (You want the kind that looks like a very long toothpick. Look in the baking aisle at the grocery store — many people use them to test cakes for doneness.)
• Alcohol (You can use regular rubbing alcohol, but if you can find 91-percent isopropyl alcohol at the drugstore get that. The closer to 100-percent alcohol you use, the better this will work.)
• Narrow container with a lid (You can use a test tube with a stopper if you have one. You could also use a small jar like you buy spices in. Make sure it is clean and dry.)

What to Do:

• 24 hours before you start, put the alcohol in the kitchen freezer. Don’t worry, it won’t freeze, but it should be ice cold before you do your experiment.  

Why you did what you did:

1. Why did I have to swish so long?

First you had to collect enough cells to work.You are also using the salts in the sports drink to begin to break the cell membrane and the membrane around the nucleus to free the DNA.

2. Why did I use the soap?

Cell membranes are made up of two layers consisting of fats, sugars and salts. The fats are on the inside of the membrane where they can avoid touching the water that surrounds the cell. Detergent molecules have two ends. One end of a detergent molecule is attracted to fat and the other end is attracted to water. When you wash your dinner plate; the fat-loving end of the dish detergent molecule attaches to the grease from your hamburger and the water-loving end attaches to the water in the sink. In the cheek solution, you were using the detergent to move the broken up cell membranes away from the DNA.

3. Why did I use pineapple juice?

Pineapple juice and meat tenderizer both contain enzymes that further help to break down the cell membrane.

4. Why did I use ice cold alcohol?

The DNA was dissolved in the water contained in the sports drink. DNA does not dissolve in alcohol. When the cold alcohol was layered on top of the cheek cell solution the DNA precipitated out of solution.

5. Why did I twirl the skewer?

Remember that famous DNA model. The DNA molecule is a very long strand with a gentle twist. Your visible DNA material is actually many thousands of these strands clumped together. Gently twirling the skewer allowed many of these strands to wind around your skewer like thread around a spool.

6. What else can I try?

Try extracting DNA from fruits like bananas or strawberries. Try leafy vegetables like spinach or kale. Take DNA from seeds like raw nuts or peas. Use about 2 cups of plant material and about half a cup of water and a tablespoon of salt instead of Gatorade. You will probably need to mix it in a blender as swishing that much in your mouth would be kind of hard!

Questions to explore:

• Do you get more DNA from using your cheeks, the fruit, the leaves or the seeds? Why do you think this is so?
• What do you have in common with a banana?
• What happens if the alcohol isn’t cold?
• Are there any steps you can leave out of the procedure and still get results?
• What other sources of DNA could you use? (Please avoid taking samples from the family pet or from your little brother!)
• Could a CSI team use this technique to collect DNA for legal purposes?
• What techniques are used for forensic science or medicine?

More science experiments:

• Science Experiments for Kids
• Cool Science Experiments for Hot Summer Days
• Oobleck Recipe: Dr. Seuss Science Project

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Hands-on Activity Balancing Liquid on a Coin: How Intermolecular Forces Work

Grade Level: 10 (9-11)

(or two 45-minute classes)

Expendable Cost/Group: US $1.00

Group Size: 2

Activity Dependency: None

Subject Areas: Biology, Chemistry, Computer Science, Physical Science, Problem Solving, Science and Technology

NGSS Performance Expectations:

TE Newsletter

Engineering connection, learning objectives, materials list, worksheets and attachments, more curriculum like this, pre-req knowledge, introduction/motivation, vocabulary/definitions, activity extensions, user comments & tips.

Wastewater engineers work to ensure that all water systems at a water treatment plant are working correctly. Their responsibilities revolve around producing clean, safe drinking water for the community. Their duties include the design and operation of the machines, systems, and equipment that receive, clean, and distribute water. Knowing the basic properties of water is an important first step in developing water treatment methods.

After this activity, students should be able to:

• Explain why water is important to life.
• Explain how the properties of water and isopropyl alcohol differ due to their molecular structures.
• Consider how the properties of water make it unique and why it has a higher evaporation point than alcohol.
• Have a cursory knowledge of water’s structure to consider its properties for future engineering.

Educational Standards Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards. All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN) , a project of D2L (www.achievementstandards.org). In the ASN, standards are hierarchically structured: first by source; e.g. , by state; within source by type; e.g. , science or mathematics; within type by subtype, then by grade, etc .

Ngss: next generation science standards - science.

NGSS Performance Expectation
HS-PS1-3. Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles. (Grades 9 - 12) Do you agree with this alignment? Thanks for your feedback!
This activity focuses on the following aspects of NGSS:
Science & Engineering Practices	Disciplinary Core Ideas	Crosscutting Concepts
Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (including students' own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future. Alignment agreement: Thanks for your feedback! Construct an explanation based on valid and reliable evidence obtained from a variety of sources (including students' own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future. Alignment agreement: Thanks for your feedback!	The structure and interactions of matter at the bulk scale are determined by electrical forces within and between atoms. Alignment agreement: Thanks for your feedback!	Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena. Alignment agreement: Thanks for your feedback!

International Technology and Engineering Educators Association - Technology

View aligned curriculum

Do you agree with this alignment? Thanks for your feedback!

Each group needs:

• science notebook for each student
• Intermolecular Forces Lab Worksheet for each student
• dropper bottle with water
• dropper bottle with isopropyl alcohol
• paper towels
• safety gloves for each student
• stopwatch, smartphone timer or watch timer

The teacher needs:

• projector and whiteboard/blackboard/chart paper for recording student ideas

Students should know how to read molecular formulas and draw atom structures. They should have learned about atomic and molecular structures as well as chemical bonding. They should understand polarity and dipole moments.

In many ways, water is a miracle liquid. It is essential for all living things on earth and it is often referred to as a universal solvent because many substances dissolve in it. Water displays unusual properties due to the ways in which individual water molecules interact with each other.

As a refresher, let’s review the properties of water. Who can name a property of water? (Answers include polarity, cohesion, adhesion, surface tension, high specific heat, and evaporative cooling.)

Today you will complete two experiments that compare the properties of water to the properties of isopropanol (a type of rubbing alcohol). Before conducting each experiment, you will make a prediction about what you think will happen. You will then read about and do the experiment. Afterwards, you will write an explanation of what was happening at the atomic level that let us observe these properties.

In many ways, water is a miracle liquid. It is essential for all living things on earth as it is one of the more abundant molecules in living cells. Approximately 60% – 70% of the human body is made up of water. Without it, life simply would not exist.

Because water is essential to life, it is important to know the basic properties of water. As it turns out, water displays some unusual properties due to the way individual water molecules interact with each other.  

A single water molecule is composed of one oxygen atom and two hydrogen atoms. Together these atoms form polar covalent bonds. (A covalent bond is a chemical bond when electrons are shared between two atoms.) A polar covalent bond forms when atoms with different electronegativities share electrons in a covalent bond. In water, the result is that each hydrogen atom shares electrons with the oxygen atom; however, the shared electrons spend more time associated with the oxygen atom than they do with hydrogen atoms. The result is that there is a slight positive charge on each hydrogen atom and a slight negative charge on the oxygen atom.

Since the hydrogen and oxygen atoms in a water molecule carry opposite (partial) charges, nearby water molecules will be attracted to each other. The attraction between the δ+ hydrogen and the δ- oxygen in adjacent molecules is called hydrogen bonding. Hydrogen bonding is an intermolecular force, which are forces between molecules in a substance. Hydrogen bonding is one of the strongest intermolecular forces. This means that neighboring water molecules are strongly attracted to one another. This is called cohesion. The property of cohesion describes the ability of water molecules to be attracted to other water molecules.

Surface Tension

Water has surface tension. Because the water molecules at the surface of liquid water have fewer neighbors, they will have an even stronger attraction to the few water molecules that are nearby. This enhanced (or greater) attraction is called surface tension. It makes the surface of the liquid water slightly more difficult to break through than the interior of the water.  Cohesion gives rise to surface tension, the capacity of a substance to withstand rupture when placed under tension or stress.

Water is often referred to as a universal solvent because many substances dissolve in it. Because of water’s polarity and structure, ionic compounds and polar molecules can readily dissolve in it. Water is, therefore, what is referred to as a solvent—a substance capable of dissolving another substance. The charged particles in water molecules will form hydrogen bonds with a surrounding layer of water molecules. When a substance readily forms hydrogen bonds with water, it can dissolve in water. Since water can dissolve so many it is important in its many roles in living systems.

Evaporation

The hydrogen bonds in water allow it to absorb and release heat energy more slowly than many other substances. Water can absorb a great deal of energy before its temperature rises.  Since the hydrogen and oxygen atoms in the molecule carry opposite partial charges, nearby water molecules are attracted to each other. The attraction between the δ+ hydrogen and the δ- oxygen in adjacent molecules is a special type of intermolecular force called hydrogen bonding that causes water molecules to “stick” together in liquid form. This force must be overcome for liquid water to become a gas. It takes a lot of energy to overcome the force of hydrogen bonding.

When enough energy has been added to water it boils and turns from liquid to gas. This happens at a temperature of 100˚C. In comparison, isopropanol turns from liquid to gas at 82.5˚C. Since the vaporization of isopropanol occurs at a lower temperature than water, this means it takes less energy to turn isopropanol into a gas, and therefore it will evaporate faster than water. Isopropanol has weaker intermolecular forces holding its molecules together, so it takes less energy (a lower temperature) to separate the molecules to enter the gas phase.

Before the Activity

• Arrange students into groups of two or let them work individually if enough materials are available. 
• Develop a system for having students get rid of lab waste and return materials to the instructor.

With Students

Part 1: Introduction (10 minutes)

• Students can work independently or with a partner through the Introduction section.
• Have students answer questions 1 and 2 of the Intermolecular Forces Lab Worksheet .
• While they work on the Introduction section, select a student or group to present their structural formulas of water and isopropyl alcohol to the class. This may be done using a document camera, or any other way you can present student work to the class. 
• Answer any questions or help correct misconceptions before having students work on Experiment #1.

Experiment #1: Penny (30 minutes)

• Hand out materials to students.
• Students work though Experiment #1 
• Place one penny on a paper towel.
• Drop water onto the surface of the penny, slowly, one drop at a time.
• Count how many drops it takes until the water spills off the penny.
• Record the number of drops to the right.
• Repeat steps A through D for isopropanol.
• Compare the number of drops of isopropanol to the number of drops of water.
• (Optional) If time, have students repeat the experiment for consistency.
• [Optional] Pause students after collecting data about number of drops of water on the penny and discuss everyone’s findings. This can be an opportunity to calculate averages and analyze the group data. 

• Have students read and mark up the “Reading” section about intermolecular forces and then develop an explanation about what happened during the experiment.
• [Optional] Have students share out their explanations and clear up misconceptions about surface tension before moving on.  Another option here is to have students define the tier three academic vocabulary (bolded) in their notes: surface tension, hydrogen bonding and intermolecular forces.

Experiment #2: Evaporation Rates (30 minutes)

• Students work though Experiment #2 

• Dip one end of a Q-tip in water. Shake off excess water.
• Dip one end of a different Q-tip in isopropanol. Shake off excess isopropanol.
• At the same time, draw (streak) the tips of each Q-tip across a paper towel in two parallel lines.
• Time how long it takes for each streak to evaporate.
• (This may take a few minutes.) Record your observations.
• [Optional] Pause students after collecting data about time taken for each liquid to evaporate and discuss findings. This can be an opportunity to calculate averages and analyze the group’s data.
• Students read and mark up the “Reading” section about hydrogen bonding and then develop an explanation about what happened during the experiment.
• [Optional] Have students share out their explanations and clear up misconceptions about hydrogen bonding.  Another option here is to have students define in their notes: surface tension, hydrogen bonding and intermolecular forces.

cohesion: Describes the ability of molecules (such as water) to be attracted to other molecules of the same makeup.

evaporation: Process by which water changes from a liquid to a gas or vapor.

hydrogen bonding: Attraction between the δ+ hydrogen and the δ- oxygen in adjacent molecules.

intermolecular force: Force between molecules in a substance.

polarity: Separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end.

solvent: The liquid in which a solute is dissolved to form a solution, or the ability to dissolve other substances.

surface tension: Attractive force exerted on the surface molecules of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area.

Pre-Activity Assessment

During the Introduction activity while the students are drawing their structural models, in the teacher should walk around and see who is doing their models accurately and who needs more support. By going over the models BEFORE completing the activity, students who are struggling to understand are given a chance to revise their thinking.

Activity Embedded (Formative) Assessment

During the introductory assignment where students learn discuss the importance of water, there is an opportunity for formative assessment by walking around and listening to partnerships share out ideas about what will happen in each of the experimental trials.

Post-Activity (Summative) Assessment

During the activity, students evaluate their predictions as accurate or inaccurate and then explain what they observed after reading the section. This helps to see students’ abilities to explain the observed phenomena. 

Safety Issues

There are no safety issues, but students should wear gloves as a best practice for maintaining a safe lab space as well as follow other lab safety protocols.

This lab is a great introductory lab to the properties of water and can be used as any pre-teaching lesson before students work with the mechanics of water or other polar substances.

Students learn about the basics of molecules and how they interact with each other. They learn about the idea of polar and non-polar molecules and how they act with other fluids and surfaces. Students acquire a conceptual understanding of surfactant molecules and how they work on a molecular level. ...

As part of a (hypothetical) challenge to help a city find the most affordable and environmentally friendly way to clean up an oil spill, students design and conduct controlled experiments to quantify capillary action in sand. Like engineers and entrepreneurs, student teams use affordable materials t...

Students are presented with the question: "Why does a liquid jet break up into droplets?" and introduced to its importance in inkjet printers. A discussion of cohesive forces and surface tension is included, as well as surface acting agents (surfactants) and their ability to weaken the surface tensi...

Contributors

Supporting program, acknowledgements.

This material is based upon work supported by the National Science Foundation under grant no. EEC 1407165— Boston University Photonics Center Research Experience for Teachers. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: October 5, 2023

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A goopy guide to extracting strawberry DNA in your kitchen

By RK Pendergrass

Updated on Apr 21, 2021 8:01 AM EDT

Maybe you’ve always wanted to be that snarky, brilliant lab technician who helps solve the case by pulling DNA from crime scenes on TV. Or perhaps you dreamed of using the genetic material of extinct species to create a Jurassic Park of your own. If you can relate to either of these scenarios, this experiment is for you.

Many of the materials scientists use to isolate DNA have simpler counterparts you can find in your own kitchen. With the help of salt, rubbing alcohol, and dish soap, you’ll be able to extract DNA from strawberries. 

Why strawberries?

Beyond the fact that you’ll be able to eat any sweet, delicious leftovers, strawberries have a rare characteristic that makes them perfect for this experiment: they have a ton of genetic material.

DNA is basically the owner’s manual to an organism. Within the two twisting strands that make this complex molecule is all the information that any living being needs to develop, function, grow, and reproduce. This data is critical, so most species keep more than one copy of it in each cell. 

[Related: Ten great science projects you can do with your kids ]

Human beings are diploid, meaning each of our cells contain two copies of our DNA. But strawberries have eight copies in every cell, which means there’s plenty for us to extract.

• Time: 20 Minutes
• Difficulty: easy
• 1 quart-sized plastic zip-top bag
• 2 to 3 large strawberries (the riper they are, the easier they’ll be to work with)
• 1 tablespoon of liquid dish soap
• ½ teaspoon of salt
• 3 tablespoons of water
• 1/3 cup of 70% isopropyl rubbing alcohol (chilled in the freezer overnight)
• Cheesecloth, a coffee filter, or a fine mesh strainer
• Two small glass cups
• A shot glass (or a test tube)
• Tweezers (or a bamboo skewer)

Instructions

• Stem the strawberries. Then put the strawberries in the zip-top bag.
• In a cup, mix the salt, water, and liquid dish soap. This is your extraction mixture. When scientists isolate DNA in a lab, they’ll often use a similar mixture of salts and detergent to break open the cell walls that protect the DNA.
• Add the extraction mixture to the zip-top bag.
• Use your fingers to press on the bag and mash the strawberries. Keep mushing until there are no large pieces remaining.
• Place the cheesecloth, filter, or strainer over the small glass cup.
• Pour the contents of the bag into the filter. Use a spoon to mash the mixture against your filter and push as much liquid into the cup as possible.
• Transfer some of the strawberry mixture to the shot glass until it’s about half full .
• Take the isopropyl alcohol out of the freezer. Ideally, it spent the entire night there. But if you forgot, make sure it spent at least three to four hours on ice so it’s nice and cold by the time you need it. The colder it is, the less it will break down those delicate DNA strands as you extract them.
• Slowly pour the isopropyl alcohol down the sides of the shot glass. Keep going until you have a 1-inch deep layer on top of the strawberry mixture. You’ll notice a cloudy white substance starts to form on the surface. That’s the DNA.
• Use your tweezers or skewer to gently collect the white clump of DNA strands.

Wait, that’s DNA? 

It is. You wouldn’t be able to see a single strand of hair from 20 feet away, but seeing a full head of hair from that distance is generally pretty easy. In a similar manner, you absolutely couldn’t see a single strand of DNA with your naked eye. But multiply eight sets of DNA by the number of cells in the strawberries you mashed up, and it adds up to one giant clump you can easily see without a microscope. 

The science behind DNA extraction

DNA is important, so it’s well protected within the cell. Getting it out is a bit like performing a heist. 

First, you’ll need brute force and special tools to break through the cell’s tough outside wall. Then you’ve got to break into the nucleus, where the DNA is safely locked away. Once you’ve done that, you’ve got to bypass the cell’s extra security measures—special destructive enzymes inside the cell that can dissolve DNA, including that of invaders such as viruses, or the strands you’re trying to extract.

Mashing the strawberries with your fingers helped to physically break the strong cell walls that protect the DNA. It also exposed more of the cells to our specialized break-in tool—the extraction mixture.

[Related: Five classic paper toys you can make when you’re bored (whether you’re in school or not) ]

The detergent helps break apart the cell wall and the nuclear membrane. They’re both made up of lipids, which also make up that fatty, oily enemy the soap fights every day on your dirty dishes.

Once the extraction mixture has breached the cell’s outer wall, it makes its way inside the nucleus. Here, the salt comes in to break apart the proteins holding the DNA together, and keeping it inside the cell. As a result, the liberated genetic strands from multiple cells clump up together.

Finally, cold alcohol is crucial in making this a science experiment instead of a soapy strawberry daiquiri. It filters out genetic material from cell debris, which unlike DNA, is soluble in alcohol. The low temperature of the alcohol also helps slow down destructive enzymes that would otherwise break down the clumped-up DNA strands. This allows them to float to the surface as a cloudy, gooey foam you can see with your naked eye, and scare your roommate with.

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The Surfing Scientist › Tricks

Cloud in a bottle

Pump a soft drink bottle full of air, pop the top and bam! A thick, white, billowing cloud will magically appear right before your eyes.

By Ruben Meerman

Creating a cloud in a bottle. (Source: Ruben Meerman/ABC Science Online)

Related Stories

• Video: Cloud in a bottle (Science Online Video)

Can't see the video? Download an mp4 [13.8 MB] version of this video .

You'll need medicinal rubbing alcohol (isopropyl alcohol, available from pharmacies and supermarkets) or methylated spirits for this experiment (so adult supervision is required for young children).

	Grab a hand operated air pump with a needle valve for inflating sports balls (soccer balls, basket balls, footballs etc.)
	Wind a strip of reusable adhesive poster hanging putty around the needle. The putty will form a seal with the neck of the bottle.
	Pour 10 to 20 millilitres of antispetic medicinal rubbing alcohol (isopropyl alcohol) or methylated spirits into an empty soft drink bottle. If you're a young whipper-snapper, please remember you need adult supervision when handling these liquids.
	Rotate and wiggle the bottle to swirl the alcohol around for 10 or 20 seconds to 'encourage' it to evaporate.
	Insert the pump to form a seal between the poster putty and the neck of the bottle. Pump air into the bottle until it feels 'full'.
	Remove the pump swiftly so that the air pressure inside the bottle drops suddenly and rapidly. The bottle will instantly fill with a dense, opaque white fog.
	If you're feeling fancy, you can fire off a few nifty fog rings at this stage by gently squeezing the bottle.
	For yet more "wow", reinsert the pump and re-pressurise the bottle while it is still full of dense white fog. As you pump, the thick white fog vanishes right before your eyes and the air turns crystal clear. If you want to make another thick, dense cloud, you'll need to shake and jiggle the bottle again before repeating the demonstration from the top.

What's going on?

You've probably heard the phrase 'high pressure, fair weather' or that a 'falling barometer' means rain approaching. This trick demonstrates the phenomenon behind those sayings.

Like water, isopropyl alcohol evaporates to form an invisible vapour. Like water vapour, that invisible isopropyl alcohol vapour can condense again to become visible liquid isopropyl alcohol. If that happens in mid-air (as opposed to on a surface), the tiny droplets produce what we call a cloud (or fog).

While the temperature and pressure inside the bottle remain steady, nothing much happens. When you start pumping air in, the internal pressure rises and the air inside the bottle becomes noticeably clearer. When you suddenly release the pressure, something rather stunning and surprising happens. A dense white cloud forms instantaneously inside the bottle. But why?

The first thing to remember is that pumping air into a bicycle or car tyre increases its temperature. You might have noticed that the pump and valve both get warmer as you pump air in. The second thing you might recall is that a drop in gas pressure causes cooling. You have almost certainly noticed this while spraying deodorant from an aerosol bottle under your armpits. The compressed gas moves from the region of high pressure inside the aerosol can to a region of much lower pressure outside the can, which causes the gas temperature to plummet. You'll notice the same thing if you let the air rush out of an inflated tyre.

So increasing pressure of a gas causes warming and decreasing pressure causes cooling. But there's one more thing. Pumping air into your soft drink bottle increases the internal temperature and therefore also increases the rate of evaporation of the isopropyl alcohol (and some water) from the wet surfaces inside. Releasing that high pressure suddenly causes a rapid and dramatic fall of temperature inside the bottle causing the isopropyl alcohol vapour (and some water vapour) to condense into tiny droplets of visible liquid. Each of those droplets reflects visible light forming a dense white fog, or cloud.

Pumping air back into the bottle causes the internal temperature to rise again so those droplets evaporate once more and the air inside turns crystal clear once more.

The same fundamental principle produces the clear skies and fair weather we associate with high pressure weather systems that form over land. The air in a high pressure system warms as it descends so the skies tend to remain cloud-free. The relatively warm rising air of a low pressure weather system, however, cools as it ascends into the atmosphere causing the invisible water vapour it carries to condense into beautiful, fluffy clouds.

Tags: physics

Published 21 May 2013

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Despite being as 'Aussie as', Ruben Meerman was actually born in Holland. He moved to Bundaberg, Queensland when he was 9 and started surfing a few years later.

He decided to study physics at school in an attempt to sit next to a hot girl. Sadly, this didn't work but it was the beginning of another beautiful relationship…with science! Read more»

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Twisting a plastic water bottle changes its volume, pressure, and temperature—and ends with a bang.

Caution: This Snack involves flying bottle caps. Use eye protection and aim safely away from yourself or anyone nearby.

• One half-liter (500 ml) clear, thin-walled plastic water bottle with screw-on cap (bottles with thin, transparent caps work best)
• Optional: isopropyl alcohol, hand-held infrared thermometer, a partner

None needed.

Note: If your water bottle happens to be full of water, drink up to empty it. It’s fine—even preferable—if there are still a few droplets of water left inside.   

Put on your goggles. 

Screw the cap on the bottle, but not all the way: The cap should be tight enough to make an airtight seal, but loose enough so you can unscrew it with a flick of your thumb. (You’ll figure this out after one or two tries.)

Grab the bottle at both ends and twist your hands in opposite directions. Twist hard—hard enough to create a narrow “waist” around the middle of the bottle. (Click to enlarge photos below.) Do you notice the bottle feeling warmer as you do this? 

Point the top of the bottle away from yourself or anyone nearby. While holding tension on the twisted bottle, remove the cap with a sideways flick of your thumb. Caution: The cap will fly off rapidly. Never aim it at another person.

Watch carefully: You may see a small cloud of mist form near the mouth of the bottle after you release the cap.  Note: If you can’t get mist to emerge from the mouth of the bottle, try adding a few drops of isopropyl alcohol, and then shake the bottle. Isopropyl alcohol’s lower vapor pressure will condense more easily than water vapor when you unscrew the cap.

If you happen to have an infrared thermometer, repeat the experiment and have a partner measure the temperature of the bottle before you squeeze it, as it is being squeezed, and then after the cap has been released. (Click photo to enlarge.)

If you want to do this Snack again, just blow into the bottle to re-inflate it and you'll be ready to go. The bottle can be used multiple times. Note: Do not re-inflate by mouth if you've previously used isopropyl alcohol in the bottle.

Did the cap go flying off? Did you hear a “pop”? Did you see mist wafting from the mouth of the bottle? All of these events tell you that your “empty” bottle was anything but empty.

When you twist the sealed bottle, you decrease the volume of the air trapped inside. When gas molecules are forced closer together in this way, the pressure inside the bottle increases. This increased pressure is what makes the cap fly across the room when released.

The “pop” you hear is caused by a sudden change in air pressure. When you release the cap, the higher-pressure air inside the bottle rushes out into the lower-pressure air inside the room. This sudden expansion creates a pressure wave that you hear as sound.

As you twist the bottle, you might feel (or measure) it getting warmer. After the cap flies, you might notice the bottle getting cooler. There is a direct relationship between pressure and temperature in a gas: increasing the pressure increases the temperature; reducing the pressure reduces the temperature. 

The mist that forms reveals that there’s not just air inside your bottle, but also some water vapor. At the relatively higher temperatures and pressures inside the twisted bottle, the water vapor remains a gas. But when you release the cap, the sudden drop in pressure and temperature causes the water to condense into visible droplets of liquid water. 

There are several other experiments and engineering challenges you can do with this Snack. For instance, you might want to investigate how far your cap will fly. Is there a relationship between the number of twists and the distance at which the cap lands?

How much does the pressure change when you twist the bottle? Can you engineer a system to determine the internal pressure of the bottle before and after twisting?

How much does the volume change? Can you figure this out using graduated cylinders, measuring cups, or other tools?

Can you use the measurements from the activities above to come up with a relationship between temperature, pressure, and volume? This relationship is known as the ideal gas law .   

As a homework assignment, ask students to bring in empty plastic water bottles. Take students outside or into a gym. With no introduction and with a twist of the wrist and a flick of the thumb pop the top off a bottle. This is an exciting way to introduce this Snack with a bang!

Let students engage in this activity after a quick demonstration (including a discussion of proper safety precautions). Note: Since you can re-inflate your bottle by mouth, each experimenter should have their own bottle. Do not re-inflate by mouth if you've previously used isopropyl alcohol in the bottle. Depending on the number of students involved a further safety precaution would be to label each bottle and cap so students can retrieve their own associated part.

After students have had a chance to launch their bottle caps, ask them what they want to do or try next. This Snack can lead to an explosion of investigations and questions relating directly relate to core scientific concepts and Science and Engineering Practices. Many questions or self-imposed challenges might arise such as: How can I make my cap go further? Who can make the most clouds in their bottle? Who can make the loudest pop? Have students take notes and make measurements; encourage them to write down their questions and design experiments to investigate further.

This Snack requires no background knowledge, just a strong wrist and fast thumb. However, this Snack can lead to discussions and lessons on a variety of gas-laws as well as kinematic concepts. It can reveal practical applications of this phenomena in modern machines—like combustion engines, refrigerators, and rockets—as well as the study of the weather (meteorology).

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DNA Extraction

You don’t need a lab or fancy equipment to find DNA—the genetic instructions for all living things. Learn how to extract DNA from strawberries in your own kitchen!

As with all science experiments, safety is extremely important. We recommend wearing safety goggles for this experiment. Parent supervision is required.

But first, what is DNA?

Supplies You’ll Need:

• Strawberries
• Isopropyl Alcohol
• Liquid Dish Soap
• Zip Lock Bag
• Small Glass Cup
• Large Glass Cup
• Measuring Cups
• Safety Goggles

Instructions:

• Put the bottle of the Isopropyl Alcohol in the freezer – about fifteen minutes before starting the experiment! You want the alcohol cold but not frozen.
• Pour 90 ml (or 18 tsp) of water into a cup.
• Then add 10 ml (or 2 tsp) of liquid dish soap to the water.
• Next add 1/4 tsp of salt to the water and soap mixture. Stir the salt until it dissolves. Once it dissolves your extraction solution has been completed.
• Pour the extraction solution into the zip-lock baggie.
• Place one strawberry in the baggie with the solution and push out as much air from the bag as possible. Then seal the bag.
• Now is the fun part! Use your hands to mash the strawberry up inside the bag. Make sure there are no large chunks of strawberry left. You want it really mushy!
• Next take the contents inside the plastic baggie and pour it through the strainer into the large glass cup. You can mash down on the mixture with a spoon to get as much liquid pushed through as possible.
• Once you have as much of the strawberry/extraction mixture in the large cup, pour the contents into the small glass cup.
• Remove the isopropyl alcohol from the freezer. Measure out 5 ml of the alcohol and pour it slowly into the strawberry/extraction mixture.
• Hold the small glass cup up to your eye. You will notice that there is a separation in the two liquids with a white layer at the very top.
• Take a tweezer and run it through the white layer. You will find that there are solid parts in the layer. This is the strawberry’s DNA. You can gently use the tweezers to pull the DNA from the glass cup.

What is happening?

As you learned in the steps above, the long stringy white pieces that you pulled out of the glass cup with your tweezers are actual strands of strawberry DNA. Strawberries have a lot of DNA when compared to other fruits. This makes the strawberry DNA not only easy to extract but also visible to see.T he extraction mixture played a crucial role in the extraction process. Strawberries are made up of cells that have an outer layer called membranes. The liquid dish soap in the extraction solution helps to dissolve those cell membranes. Inside those cells are also protein chains that hold nucleic acids. The salt in the extraction solution will break up the protein chains and release the strawberry’s DNA. You added isopropyl alcohol to keep the DNA from being dissolved in the extraction solution.

Science Vocabulary:

• DNA- (n.) is the building blocks of any organism. It acts a guidebook to instruct the body on how to develop and function.
• Cell Membrane – (n.) the outside layer or wall of a cell.
• Protein Chains- (n.) large chains of amino acids.
• Amino Acids – (n.) the necessary parts of every cell in your body that produce proteins in order for you to survive.
• Nucleic Acids – (n.) the building blocks of any organism – DNA is just one type of nucleic acid.
• Dissolve – (v.) the act of something breaking up and disappearing into something else.

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How to Cook an Egg With Alcohol Without Heat

Did you know that you can cook an egg without heat ? Cooking occurs when proteins are denatured, so any process that produces a chemical change in protein can cook food. Here’s a simple science project that demonstrates you can cook an egg in alcohol. The resulting egg resembles one that has been hard boiled.

Basically, all you need for this cooking chemistry project is a raw egg and alcohol:

For the alcohol, you can use vodka, 151 rum, or any other high-proof ethanol that is fit for human consumption . The higher the alcohol percentage or proof, the faster the chemical reaction and cooking occurs. While the egg will cook using other types of alcohol ( denatured alcohol , rubbing alcohol, isopropyl alcohol, methanol), these types of alcohol are toxic and the cooked egg will be inedible.

Here’s how to cook the egg:

• Pour the alcohol into a glass or other small container.
• Crack the egg and place it in the alcohol. Make certain the egg is completely covered by the liquid.
• Wait for the egg to cook. After the egg white whitens, allow more time for the yolk to cook.

Depending on the percentage of alcohol, the reaction takes at least an hour. The egg would cook a lot more quickly if you boiled it the regular way; you have to wait for the alcohol to work its way into the egg.

The egg cooked in alcohol is edible, but it contains a high concentration of alcohol. If you choose to eat it, probably its best use is in a cocktail.

How It Works

The egg white consists mostly of the protein albumin. Within a few minutes of adding the egg to the alcohol, the translucent egg white starts to turn cloudy. The alcohol participates in a chemical reaction, denaturing or changing the conformation of the protein molecules so they can form new linkages with each other. As the alcohol diffuses into the egg white, the reaction proceeds and the egg white turns white.

The egg yolk contains some protein, but also a lot of fat, which is not as affected by the alcohol. Within 1 to 3 hours, depending mainly on alcohol concentration, the egg white is white and solid and the egg yolk is firm.

Cooking also kills nasty disease-causing pathogens that could cause food poisoning. Alcohol, like heat, is an excellent disinfectant.

More Ways to Cook Without Heat

Alcohol is not the only chemical that can cook food without heat. For example, you can cook an egg in vinegar. This reaction, called pickling, results from the acetic acid in the vinegar. Acetic acid lowers the pH in food to 4.6 or lower, killing more bacteria. The low pH and exclusion of air promotes fermentation by a Lactobacillus bacteria. The bacteria produce lactic acid that preserves the food. Pickling changes the flavor and texture of food.

Salt or brine preserves food by changing the osmotic pressure . This deters microbial growth, plus the process seasons food and enhances tenderness. Brining is often combined with pickling.

• Kenji López-Alt, J. (2015). The Food Lab: Better Home Cooking Through Science. W. W. Norton & Company. ISBN 978-0393081084.
• McGee, Harold (2004). On Food and Cooking: The Science and Lore of the Kitchen . New York: Scribner. ISBN 0-684-80001-2.
• Rhee, M.S.; Lee, S.Y.; Dougherty, R.H.; Kang, D.H. (2003). “Antimicrobial effects of mustard flour and acetic acid against Escherichia coli O157:H7, Listeria monocytogenes , and Salmonella enterica serovar Typhimurium”. Appl Environ Microbiol . 69 (5): 2959–63. doi: 10.1128/aem.69.5.2959-2963.2003

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January 31, 2013

Squishy Science: Extract DNA from Smashed Strawberries

A genetically geared activity from Science Buddies

By Science Buddies

Key concepts DNA Genome Genes Extraction Laboratory techniques

Introduction Have you ever wondered how scientists extract DNA from an organism? All living organisms have DNA, which is short for deoxyribonucleic acid; it is basically the blueprint for everything that happens inside an organism’s cells. Overall, DNA tells an organism how to develop and function, and is so important that this complex compound is found in virtually every one of its cells. In this activity you’ll make your own DNA extraction kit from household chemicals and use it to separate DNA from strawberries.     Background Whether you’re a human, rat, tomato or bacterium, each of your cells will have DNA inside of it (with some rare exceptions, such as mature red blood cells in humans). Each cell has an entire copy of the same set of instructions, and this set is called the genome. Scientists study DNA for many reasons: They can figure out how the instructions stored in DNA help your body to function properly. They can use DNA to make new medicines or genetically modify crops to be resistant to insects. They can solve who is a suspect of a crime, and can even use ancient DNA to reconstruct evolutionary histories!

To get the DNA from a cell, scientists typically rely on one of many DNA extraction kits available from biotechnology companies. During a DNA extraction, a detergent will cause the cell to pop open, or lyse, so that the DNA is released into solution. Then alcohol added to the solution causes the DNA to precipitate out. In this activity, strawberries will be used because each strawberry cell has eight copies of the genome, giving them a lot of DNA per cell. (Most organisms only have one genome copy per cell.)

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Rubbing alcohol

Measuring cup

Measuring spoons

Dishwashing liquid (for hand-washing dishes)

Glass or small bowl

Cheesecloth

Tall drinking glass

Three strawberries

Resealable plastic sandwich bag

Small glass jar (such as a spice or baby food jar)

Bamboo skewer, available at most grocery stores. (If you use a baby food or short spice jar, you could substitute a toothpick for the skewer.)

Preparation

Chill the rubbing alcohol in the freezer. (You’ll need it later.)

Mix one half teaspoon of salt, one third cup of water and one tablespoon of dishwashing liquid in a glass or small bowl. Set the mixture aside. This is your extraction liquid. Why do you think there is detergent in the extraction liquid?

Completely line the funnel with cheesecloth. Insert the funnel tube into the tall drinking glass (not the glass with the extraction liquid in it).

Remove and discard the green tops from the strawberries.

Put the strawberries into a resealable plastic sandwich bag and push out all of the extra air. Seal the bag tightly.

With your fingers, squeeze and smash the strawberries for two minutes. How do the smashed strawberries look?

Add three tablespoons of the extraction liquid you prepared to the strawberries in the bag. Push out all of the extra air and reseal the bag. How do you think the detergent and salt will affect the strawberry cells?

Squeeze the strawberry mixture with your fingers for one minute. How do the smashed strawberries look now?

Pour the strawberry mixture from the bag into the funnel. Let it drip through the cheesecloth and into the tall glass until there is very little liquid left in the funnel (only wet pulp remains). How does the filtered strawberry liquid look?

Pour the filtered strawberry liquid from the tall glass into the small glass jar so that the jar is one quarter full.

Measure out one half cup of cold rubbing alcohol.

Tilt the jar and very slowly pour the alcohol down its side. Pour until the alcohol has formed approximately a one-inch-deep layer on top of the strawberry liquid. You may not need all of the one half cup of alcohol to form the one-inch layer. Do not let the strawberry liquid and alcohol mix.

Study the mixture inside of the jar. The strawberry DNA will appear as gooey clear/white stringy stuff. Do you see anything in the jar that might be strawberry DNA? If so, where in the jar is it?

Dip the bamboo skewer into the jar where the strawberry liquid and alcohol layers meet and then pull up the skewer. Did you see anything stick to the skewer that might be DNA? Can you spool any DNA onto the skewer?    

Extra: You can try using this DNA extraction activity on lots of other things. Grab some oatmeal or kiwis from the kitchen and try it again! Which foods give you the most DNA?

Extra: If you have access to a milligram scale (called a balance), you can measure how much DNA you get (called a yield). Just weigh your clean bamboo skewer and then weigh the skewer again after you have used it to fish out as much DNA as you could from your strawberry DNA extraction. Subtract the initial weight of the skewer from its weight with the DNA to get your final yield of DNA. What was the weight of your DNA yield?

Extra: Try to tweak different variables in this activity to see how you could change your strawberry DNA yield. For example, you could try starting with different amounts of strawberries, using different detergents or different DNA sources (such as oatmeal or kiwis). Which conditions give you the best DNA yield?

Observations and results Were you able to see DNA in the small jar when you added the cold rubbing alcohol? Was the DNA mostly in the layer with the  alcohol and between the layers of alcohol and strawberry liquid?

When you added the salt and detergent mixture to the smashed strawberries, the detergent helped lyse (pop open) the strawberry cells, releasing the DNA into solution, whereas the salt helped create an environment where the different DNA strands could gather and clump, making it easier for you to see them. (When you added the salt and detergent mixture, you probably mostly just saw more bubbles form in the bag because of the detergent.) After you added the cold rubbing alcohol to the filtered strawberry liquid, the alcohol should have precipitated the DNA out of the liquid while the rest of the liquid remained in solution. You should have seen the white/clear gooey DNA strands in the alcohol layer as well as between the two layers. A single strand of DNA is extremely tiny, too tiny to see with the naked eye, but because the DNA clumped in this activity you were able to see just how much of it three strawberries have when all of their octoploid cells are combined! (“Octoploid” means they have eight genomes.)

More to explore Do-It-Yourself Strawberry DNA, from the Tech Museum of Innovation, Stanford School of Medicine About Genetics , from the Tech Museum of Innovation, Stanford School of Medicine DNA Extraction Virtual Lab, from Learn Genetics, the University of Utah Do-It-Yourself DNA , from Science Buddies

This activity brought to you in partnership with  Science Buddies

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M&Ms are great but have you ever noticed that if your fingers are a little wet, the candy coating begins to dissolve and you see color on your fingers? If the coating dissolves in water, do you think it will dissolve in other liquids?

Let’s find out.

1. Label your three cups water , alcohol , and oil .

2. Add 1 tablespoon of water, isopropyl alcohol, and oil to its labeled cup.

3. Take three M&Ms of the same color and put one in each cup.

4. Swirl each cup for about 20 seconds to see if one liquid is better than another at dissolving the candy coating.

What to expect

The coating on the M&M in the water will dissolve the most. You may even see the chocolate on the inside. There will be a little dissolving in the alcohol but not nearly as much as in the water. In the oil, you probably will not be able to see any dissolving.

What's happening in there?

Why does the color come off differently in each liquid? The candy coating is made up of coloring and sugar. The coloring and the sugar molecules both have positive and negative charges on them.

The water molecule has positive and negative charges so it can attract and dissolve the color and sugar pretty well.

The alcohol molecules don’t have as many positive and negative areas as the water. The alcohol molecules can’t attract the coloring and sugar molecules as well as the water so the candy coating doesn’t dissolve well in alcohol.

The oil molecules have no positive and negative areas. They don’t attract the coloring or sugar molecules so the candy coating doesn’t dissolve at all in oil.

What else could you try?

You’ve seen that water is the best liquid for dissolving the candy coating from an M&M. But have you ever tried putting two or more M&Ms in water at the same time? You can get some pretty cool-looking patterns.

The coating comes off the M&M in a round shape surrounding the M&M. The dissolved coatings from different M&Ms drift toward each other and touch. The colors seem to form a line and don’t seem to mix right away.

1. Pour water in the plate until it covers the bottom and is about as deep as an M&M.

2. Place two or more M&Ms near each other in the center of the plate.

3. Do not stir the water or bump the plate.

4. Watch for about 1-2 minutes.

5. Try different arrangements of M&Ms.

What’s happening in there?

Why don't the colors mix?

It may seem weird that the colors don’t mix right away. But if you think about it, we usually stir or shake things if we want them to mix. We usually don’t just let two liquids touch and expect them to mix right away. As the molecules from the dissolved coatings interact with each other, they will mix but it takes some time.

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Effect of Temperature on the Whoosh Bottle

I recently had the opportunity to attend a conference of the Associated Chemistry Teachers of Texas (ACT2). I had  great time interacting with and learning from a whole bunch of wonderful chemical educators from the great state of Texas. One of the most interesting things I learned was in reference to the classic “whoosh bottle” experiment, which is powered by the combustion of isopropyl alcohol:

2 C 3 H 7 OH(l) + 9 O 2 (g) → 6 CO 2 (g) + 8 H 2 O(g)        Equation 1

Interestingly, the reaction in this experiment yields different results when conducted at different temperatures (Video 1).

Video 1: Effect of temperature on a combustion reaction , pchemstud  on TikTok. June 20, 2022.

That’s quite a significant difference! When I shared this video online, I had a few people comment that the difference observed might not be due to a faster reaction rate at the higher temperature. Instead, it was argued that the difference was because more alcohol vapor is contained in the warm bottle as compared to the cold one, on account of the higher vapor pressure of alcohol at higher temperatures. We can see this quantitatively by first noting the vapor pressures of isopropyl alcohol at 5.0 o C (12 mmHg = 0.016 atm) and 32 o C and 20 o C  (32 mm Hg = 0.042 atm). 1 Because the volume of the bottle is known (5 gallons = 19 L), we can then use the idea gas law (as n = PV/RT) to calculate the moles of isopropyl alcohol present in each bottle:

bottle_temps.png

That’s about 2.5 times more alcohol vapor in the warm bottle over the cool one. Because reaction rates increase with higher concentration of reactants, perhaps the effect observed really is due to the presence of more fuel in the warm bottle.

I decided to look into this a bit further, attempting to use the Arrhenius Equation to compare the kinetic rates of the reaction at the different temperatures:

equation_2.png

Where k is the rate constant for the reaction, A is the pre-exponential factor, E a is the activation energy for the reaction, T is temperature, and R = 8.314 J mol -1 K -1 . The ratio of the values of the rate constants at 20 o C (293 K) and 5 o C (278 K) would therefore be:

equation_3.png

Substitution of 125 kJ mol -1 as an estimate for the activation energy of the combustion of isopropanol 2-4 into Equation 3 yields:

substituting_in_equation_3.png

Therefore, this analysis suggests combustion in the warm bottle should proceed about 16 times faster than in the cold bottle.

So which is it?

Well, 16 (kinetic temperature effect) is over 5 times bigger than 2.5 (amount of fuel effect), so perhaps these analyses should lead me to conclude that combustion in the hot “whoosh bottle” goes faster because of the effect of temperature on reaction rates – not from the presence of more fuel in the hot bottle as compared to the cool one. But honestly, I’m not sure. I’m not entirely comfortable with my estimation of the activation energy of isopropanol combustion used in the Arrhenius analysis. I’m also not sure that the Arrhenius  analysis I did is entirely appropriate. Furthermore, what I am confident about is that multiple types of combustion took place in the warm bottle but not in the cool bottle. I say this because I saw soot had formed on the outside of the warm bottle, but not the cool one after the reaction subsided (look for this carefully in Video 1). The formation of soot indicates incomplete combustion, in which carbon monoxide (Equation 4) and soot (Equation 5) are formed:

C 3 H 7 OH(l) + 3 O 2 (g) → 3 CO(g) + 4 H 2 O(g)                        Equation 4

2 C 3 H 7 OH(l) + 3 O 2 (g) → 6 C (s, soot) + 8 H 2 O(g)                Equation 5

If multiple reactions occurred in the warm bottle but only complete combustion in the cool bottle, this complicates matters further. In the end, if I had to guess, I’d venture that both effects play a role.

But I’d like to know what you think. Why does the “whoosh bottle” go faster at higher temperatures? Is it simply because of the effect of temperature on reaction kinetics? Or is it because more alcohol vapor is present in the warmer bottle due to the higher vapor pressure of alcohol at increased temperature? Might both impact the reaction rate? What thoughts or criticisms do you have on my analysis presented here? Do you have any suggestions for experiments I might try to test which of these two possibilities better describes the observations? I look forward to hearing from you, and to carrying out more experiments on the effect of temperature on the “whoosh bottle.”

Happy Experimenting!

Acknowledgement:

Thanks to Dr. Bob Shelton from Texas A&M University in San Antonio for showing me this demonstration.

References:

• Parks, G. S.; Barton, B. J. Am. Chem. Soc. 1928 , 50 , 24-26.
• Vandenabeele, H.; Corbeels, R.; van Tiggelen, A. Combustion and Flame , 1960 , 4 , 253-260.
• Frassoldati, A.;  Cuoci, A.;  Faravelli, T.; Niemann, U.; Ranzi, E.; , Seiser, R.; Seshadri, K.   Combustion and Flame , 1960 , 4 , 253-260.
• I could not find a literature value for experimentally measured values for the activation energy of the combustion of isopropanol. However, reference 3 does mention a value of less than 35 kcal mol -1 (146 kJ mol -1 ) based on a combination of measurements and theoretical calculation. Further, reference 2 cites 36.5 kcal mol -1 (153 kJ mol -1 ) as the activation energy for methane combustion. These considerations suggest 125 kJ mol -1 is a fair estimate.

Safety: Video Demonstration

Demonstration videos presented here are not meant as tools to teach chemical demonstration techniques. They are meant as a tool for classroom use. The demonstrations may present safety hazards or show phenomena that are difficult for an entire class to observe in a live demonstration.

Those performing the demonstrations shown in this video have been trained and adhere to best safety practices.

Anyone thinking about performing a chemistry demonstration should first read and then adhere to the  ACS Safety Guidelines for Chemical Demonstrations (2016)  These guidelines are also available at ChemEd X.

General Safety

For Laboratory Work:  Please refer to the ACS  Guidelines for Chemical Laboratory Safety in Secondary Schools (2016) .  

For Demonstrations: Please refer to the ACS Division of Chemical Education Safety Guidelines for Chemical Demonstrations .

Other Safety resources

RAMP : Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies

Science Practice: Asking Questions and Defining Problems

Asking questions and defining problems in grades 9–12 builds from grades K–8 experiences and progresses to formulating, refining, and evaluating empirically testable questions and design problems using models and simulations.

questions that challenge the premise(s) of an argument, the interpretation of a data set, or the suitability of a design.

Scientific questions arise in a variety of ways. They can be driven by curiosity about the world (e.g., Why is the sky blue?). They can be inspired by a model’s or theory’s predictions or by attempts to extend or refine a model or theory (e.g., How does the particle model of matter explain the incompressibility of liquids?). Or they can result from the need to provide better solutions to a problem. For example, the question of why it is impossible to siphon water above a height of 32 feet led Evangelista Torricelli (17th-century inventor of the barometer) to his discoveries about the atmosphere and the identification of a vacuum.

Questions are also important in engineering. Engineers must be able to ask probing questions in order to define an engineering problem. For example, they may ask: What is the need or desire that underlies the problem? What are the criteria (specifications) for a successful solution? What are the constraints? Other questions arise when generating possible solutions: Will this solution meet the design criteria? Can two or more ideas be combined to produce a better solution?

Science Practice: Constructing Explanations and Designing Solutions

Constructing explanations and designing solutions in 9–12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories.

Constructing explanations and designing solutions in 9–12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories. Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (including students’ own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future.

Science Practice: Engaging in Argument from Evidence

Science practice: planning and carrying out investigations.

Planning and carrying out investigations in 9-12 builds on K-8 experiences and progresses to include investigations that provide evidence for and test conceptual, mathematical, physical, and empirical models.

Planning and carrying out investigations in 9-12 builds on K-8 experiences and progresses to include investigations that provide evidence for and test conceptual, mathematical, physical, and empirical models. Plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence, and in the design: decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of the data (e.g., number of trials, cost, risk, time), and refine the design accordingly.

Science Practice: Using Mathematics and Computational Thinking

Mathematical and computational thinking at the 9–12 level builds on K–8 and progresses to using algebraic thinking and analysis, a range of linear and nonlinear functions including trigonometric functions, exponentials and logarithms, and computational tools for statistical analysis to analyze, represent, and model data. Simple computational simulations are created and used based on mathematical models of basic assumptions. Use mathematical representations of phenomena to support claims.

HS-PS1 Matter and Its Interactions

Matter and its Interactions help students formulate an answer to the question, “How can one explain the structure, properties, and interactions of matter?” The PS1 Disciplinary Core Idea from the NRC Framework is broken down into three subideas: the structure and properties of matter, chemical reactions, and nuclear processes. Students are expected to develop understanding of the substructure of atoms and to provide more mechanistic explanations of the properties of substances. Chemical reactions, including rates of reactions and energy changes, can be understood by students at this level in terms of the collisions of molecules and the rearrangements of atoms. Students are able to use the periodic table as a tool to explain and predict the properties of elements. Using this expanded knowledge of chemical reactions, students are able to explain important biological and geophysical phenomena. Phenomena involving nuclei are also important to understand, as they explain the formation and abundance of the elements, radioactivity, the release of energy from the sun and other stars, and the generation of nuclear power. Students are also able to apply an understanding of the process of optimization in engineering design to chemical reaction systems. The crosscutting concepts of patterns, energy and matter, and stability and change are called out as organizing concepts for these disciplinary core ideas. In the PS1 performance expectations, students are expected to demonstrate proficiency in developing and using models, planning and conducting investigations, using mathematical thinking, and constructing explanations and designing solutions; and to use these practices to demonstrate understanding of the core ideas.

*More information about this category of NGSS can be found at  https://www.nextgenscience.org/dci-arrangement/hs-ps1-matter-and-its-interactions . 

" Matter and its Interactions help students formulate an answer to the question, “How can one explain the structure, properties, and interactions of matter?” The PS1 Disciplinary Core Idea from the NRC Framework is broken down into three subideas: the structure and properties of matter, chemical reactions, and nuclear processes. Students are expected to develop understanding of the substructure of atoms and to provide more mechanistic explanations of the properties of substances. Chemical reactions, including rates of reactions and energy changes, can be understood by students at this level in terms of the collisions of molecules and the rearrangements of atoms. Students are able to use the periodic table as a tool to explain and predict the properties of elements. Using this expanded knowledge of chemical reactions, students are able to explain important biological and geophysical phenomena. Phenomena involving nuclei are also important to understand, as they explain the formation and abundance of the elements, radioactivity, the release of energy from the sun and other stars, and the generation of nuclear power. Students are also able to apply an understanding of the process of optimization in engineering design to chemical reaction systems. The crosscutting concepts of patterns, energy and matter, and stability and change are called out as organizing concepts for these disciplinary core ideas. In the PS1 performance expectations, students are expected to demonstrate proficiency in developing and using models, planning and conducting investigations, using mathematical thinking, and constructing explanations and designing solutions; and to use these practices to demonstrate understanding of the core ideas."

HS-PS1-2 Chemical Reactions

Students who demonstrate understanding can construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.

*More information about all DCI for HS-PS1 can be found at  https://www.nextgenscience.org/dci-arrangement/hs-ps1-matter-and-its-interactions and further resources at https://www.nextgenscience.org .

Assessment is limited to chemical reactions involving main group elements and combustion reactions.

Examples of chemical reactions could include the reaction of sodium and chlorine, of carbon and oxygen, or of carbon and hydrogen.

HS-PS1-5 Rates of Reactions

Students who demonstrate understanding can apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.

Assessment is limited to simple reactions in which there are only two reactants; evidence from temperature, concentration, and rate data; and qualitative relationships between rate and temperature.

Emphasis is on student reasoning that focuses on the number and energy of collisions between molecules.

All comments must abide by the ChemEd X Comment Policy , are subject to review, and may be edited. Please allow one business day for your comment to be posted, if it is accepted.

On whether the concentration or temperature influences more..

I think that to verify this, it is enough to measure the time it takes to carry out each of the reactions, since it is very easy to calculate that time on video, even if it is approximate. I have taken the trouble to measure this time, and in the first reaction at 5ºC it takes approximately 5 s to complete and in the second at 20ºC it takes approximately 2 s, then the first is 2.5 times slower than the second or vice versa the second is 2.5 times faster, curiously exactly the largest amount of alcohol there is, this is no coincidence. If we remember the kinetics of the reactions, in the first place we have the concentration of reagents and secondly the Temperature, and studying it like this in that order is not by chance seeing what happened. It can be assumed that it is at the same concentrations where the effect of temperature is relevant, but at different concentrations the temperature hardly has any effect on the kinetics of the reaction.

(Sobre si influye mas la concentración o la temperatura. Creo que para comprobar esto es suficiente con medir el tiempo que tarda en realizarse cada una de las reacciones, ya que esta en video es muy fácil calcular ese tiempo, aunque sea aproximado. M ehe tomado la moletia de medir dicho tiempo, y en la primera reaccion a 5ºC tarda aproximadamente 5 s en completarse y en la segunda a 20ºC tarda aproximadamente 2 s, luego la primera es 2,5 veces mas lenta que la segunda o al revés la segunda es 2,5 veces mas rápida, curiosamente exactamente la cantidad mayor de alcohol que hay, esto no es casualidad. Si recordamos la cinética de las reacciones, en primer lugar tenemos la concetración de reactivos y en segundo lugar la Temperatura, y estudiarlo así en ese orden no es casualidad viendo lo ocurrido. Se puede suponer que es a iguales concentraciones donde el efecto de la temperatura es relevante, pero a distintas concentraciones la temperatura apenas tiene efectos sobre la cinética de la reacción.)

Nice analysis!

Hi Josefpm,

Thank you so much for taking the time to analyze how long it takes for each of these reactions to complete. What a great idea! It is indeed very interesting that the reaction happens 2.5 times more quickly at a warmer temperature than at a cooler temperature, and that this matches the estimated difference in concentration of the vapor in each container! In my opinion, this does not demonstrate that the reaction is only influenced by the differences in concentration, and that temperature has no effect on the kinetics. I would argue that the match in concentration and reaction time could indeed be coincidence. I say this because we certainly know that temperature influences the rates of reactions. Of course concentration does as well, as you rightly point out.

What do you think, Josepfpm? Am I off base? How might you provide further evidence to convince me that the difference in reaction kinetics is due only to concentration and not temperature?  

I wonder what others think about this. Anyone else want to chime in?   

Again, thanks so much for the discussion!

I agree but not completely ;-)

Oh, thanks for taking the time to answer, I agree with you, that does not mean that the temperature does not affect it, but I do believe, as I indicated, that at different concentrations the determining factor is the concentration and not the temperature, although the temperature has its effect, this effect is much less. That is why I suppose that at the same concentration the effect of temperature or at very high temperatures would be much more decisive. could it be coincidence? Yes, it could be, but wouldn't it be too much of a coincidence? and more when we know that the concentration in a factor that influences the speed of reaction. It would be a matter of carrying out the experiment with other concentrations and measuring the speed and seeing if that relationship is maintained or, as he says, it was coincidence. The question would not be to see if the temperature affects or not the speed of reaction, or if the concentration affects or not, it is evident that both affect; The question would be to what extent do they affect? which is more decisive? It occurs to me that you can try carrying out the HCl+NaHCO3 reaction, using the same concentration at two temperatures and measuring the reaction time, it would be approximate, for example at room temperature and inside a refrigerator or cold room... umm I'll try to do it this summer if I have time...

(Oh, gracias por tomarte tiempo en contestar, coincido con usted, eso no indica que la temperatura no afecte, pero si creo, como indico, que a diferentes concentraciones el factor determinante es la concentración y no la temperatura, aunque la temperatura tenga su efecto este efecto es mucho menor. Por eso supongo que a igual concentración si sería mucho mas determinante el efecto de la temperatura o a muy altas temperaturas. ¿podría ser casualidad? Si, podría ser pero, ¿no sería demasiada casualidad? y más cuando sabemos que la concentración en un factor que influye en la velocidad de reacción. Sería cuestión de realizar el experimento con otras concentraciones y medir la velocidad y ver si se mantiene ese relación o como dice fue casualidad. La cuestión no sería ver si la temperatura afecta o no a la velocidad de reacción, o si la concentración afecta o no, es evidente que ambas afectan; la cuestión sería ¿en qué medida afectan? ¿cual es mas determinante? Se me ocurre que se puede probar a realizar la reacción del HCl+NaHCO3, usando al misma concentración a dos temperaturas y medir el tiempo, de reacción, sería aproximado, por ejemplo a temperatura ambiente y dentro de un refrigerador o cámara frigorífica... umm intentaré hacerlo este verano si tengo tiempo...)  

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Topic 1.1, Part 2: Water Virtual Lab — Comparing Water and Isopropyl Alcohol (v2.0)

Looking for a student learning guide? You’ll find a link on the main menu for your course. Use the “Courses” menu above.

Introduction

In the previous tutorial , we looked at the chemistry of water. We saw how water’s polar structure allows water molecules to form hydrogen bonds with other water molecules. In this tutorial, we’ll do a virtual lab that lets us look at water’s unique properties: properties that result from hydrogen bonding.

If it suits your learning style, you might want to start by watching the video below. 

1. A (virtual) lab comparing water and alcohol: What you’ll need

To get a sense of the properties of water, we’re going to do a virtual lab comparing water to alcohol. Since real science is always preferable to virtual science, I want to encourage you to get the supplies for this lab and to independently try the activities. Alternatively, your teacher might be taking you through this lab in a classroom setting.

If you’re working independently, here’s what you’ll need:

• SAFETY NOTE : isopropyl alcohol is poisonous. Don’t drink it. Wear goggles or safety glasses to protect your eyes.
• Also, if you can’t get isopropyl alcohol, but other types of alcohol are available (such as ethyl alcohol), the lab should work perfectly well.
• Two eye droppers or plastic pipettes. If you’re using pipettes, label them, and put one in the water, and the other in the alcohol. If you’re using droppers, fill one with water, and one with alcohol.
• A few small beakers, glasses, or cups.
• Two small paper clips
• Two pennies (or two small squares of wax paper if you can’t get a penny)
• Two teaspoons to do some stirring
• Table salt (about two teaspoons).

2. Background: Comparing Water and Isopropyl Alcohol

Based on our last tutorial, you already know a lot about water. Here’s a quick review of water’s key properties.

• Water is a polar molecule.
• The oxygen side of the molecule has a partially negative charge (? – )
• The hydrogens, on the other side, have a partially positive charge(? + ).
• As a result, water molecules form hydrogen bonds, interacting as shown below.

Water: structural formula	Water molecules forming hydrogen bonds

Here’s isopropyl alcohol.

Isopropyl alcohol: structural formula	Isopropyl alcohol. This is a model. Each sphere is an atom, connected by a single covalent bond. White = hydrogen, black = carbon, and red = oxygen.

Here’s what you need to know about isopropyl alcohol:

• Most of the isopropyl alcohol (the three carbons and the hydrogens attached to them) is non-polar.
• One part of isopropyl alcohol is slightly polar. It’s the oxygen and hydrogen on top. Notice that in the structural formula on the left, the hydrogen (H) has a ? +  (partial positive charge) next to it, and the oxygen has a ? –  (partial negative charge)

So, isopropyl alcohol is slightly polar. But it’s much less polar than water is.

	less polar than water

Knowing that, let’s do a few experiments where we compare them.

3. Six Observations/Experiments Comparing Water and Alcohol

Please record your predictions for each of the experiments that follow on your student learning guide. You’ll learn a lot more if you make a prediction before clicking “show the answer.”

[qwiz style = ” width: 600px !important; min-height: 400px !important; border: 3px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-Water v Alcohol Virtual Lab (2.0)”]

[h]Water v. alcohol: Virtual Lab

[q] EXPERIMENT 1:   Let’s start by predicting the way that a single drop of water and a single drop of alcohol will look when you put them on a surface like a penny or wax paper. Do the following

• In your notes, draw a picture of how you think a single drop of water on a penny will look, compared with how a single drop of alcohol will look.
• Below your drawing, explain why you think the two will be different. 
• Once you’ve made your prediction, do the experiment if you have materials.
• Click “show the answer.”

[c]IMKgc2hvdyB0 aGUgYW5zd2Vy[Qq]

[f]IEFOU1dFUg==

Cg==Cg==Cg==

[Qq]

Because the water molecules are polar, they grab onto one another through hydrogen bonds. The mutual attraction of water molecules is called cohesion . Cohesion pulls a drop of water into a spherical shape that allows for the maximum number of bonds. Though gravity is trying to pull the water molecules down, the hydrogen bonds keep the water droplet in a spherical shape. Because alcohol is so much less polar, it can’t resist gravity, and all of the molecules are pulled down into a flat sheet over the penny’s surface.

[q] EXPERIMENT 2: Use what you just observed to predict the following: How many drops of water can you put onto a penny before the water spills over the side? How many drops of alcohol before the alcohol spills over the side? Make a prediction, give it a try, and, most importantly, explain what’s happening.

When you’re ready, click “show the answer” to see the results and verify your prediction.

[c]wqBzaG93IHRo ZSBhbnN3ZXI=[Qq]

Many variables influence the exact number of drops, but you should have been able to pile many more drops of water on the penny than drops of alcohol. Again, this is because the water molecules, which form hydrogen bonds with one another, have much more cohesion than alcohol molecules. Cohesion forces the water to form a sphere, with more and more water molecules filling that sphere (until gravity overcome hydrogen bonding, and water spills out over the side.

With less polarity, the alcohol can’t resist gravity. Its molecules are pulled down into a flat sheet over the penny’s surface that can accommodate many fewer drops than the hydrogen-bond induced sphere that’s on the penny with water.

[q] EXPERIMENT 3: Speed of Evaporation in Water and Alcohol

This video compares the evaporation of a drop of alcohol (left) with a drop of water (right). I used my phone as both a surface and a timer (and then speeded up the video about 60 times, so that each minute on the clock goes by in a second). If you can do the same, go ahead and try it.

Explain why the evaporation times for water and alcohol are so different.

VGhlIHNwZWNpZmljIHByb3BlcnR5IHRoYXQgd2UmIzgyMTc7cmUgY29tcGFyaW5nIGhlcmUgaXMgdGhlIA== aGVhdCBvZiB2YXBvcml6YXRpb24= 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

Because alcohol is mostly a nonpolar molecule (with just a bit of polarity) there’s very little attraction between one alcohol molecule and the next. Consequently, when alcohol molecules absorb enough energy from the environment to start moving around quickly,  they can easily accelerate to a high enough speed to jump away from the surface of the liquid. No hydrogen bonds are holding them back. As molecule after molecule of alcohol jumps away from the liquid, the volume of the liquid decreases…until all of it has evaporated.

[q] EXPERIMENT 4: Predict how water and alcohol will feel when you place a few drops of each liquid on your skin.

• In your notes, predict how each liquid will feel when placed on your skin. Below your prediction, explain why you think the two will be different. 
• If you have the materials, place the same number of drops of alcohol and water on different areas of your skin (for example, different parts of the back of your hand). If you can, work with a partner, and have your partner place the drops on your hand while your eyes are closed. Without looking, can you tell which drop was which?  Afterward, click on “show the answer” to see if your results correspond with what I’ve written below.

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[Qq]

[q] EXPERIMENT 5: Now let’s predict how easily salt will dissolve in water and alcohol.

• In your notes, predict whether or not salt will dissolve in water, and whether or not salt will dissolve in an equal amount of alcohol. 
• place a small amount of water (100 mL) in a cup, and an equal amount of alcohol in a second cup.
• Use one teaspoon to put about 1/2 a teaspoon of salt in the water cup. Stir. Record what happens.
• Using a second teaspoon, put about 1/2 a teaspoon of salt into the alcohol cup. Stir. Record what happens.
• If you don’t have the materials, just click on “show the answer” to see the results and verify your prediction.

V2hpbGUgc2FsdCBxdWlja2x5IGRpc3NvbHZlcyBpbiB3YXRlciwgaXQgd29uJiM4MjE3O3QgZGlzc29sdmUgaW4gYWxjb2hvbC4=

Table salt is sodium chloride (NaCl). Sodium chloride is an ionic compound, held together by ionic bonds between positively charged sodium ions and negatively charged chlorine ions. When water and salt are mixed, water’s polarity makes dissolving the salt easy. The positively charged side of water pulls the chlorine ions away from the salt crystal. The negatively charged side of water pulls the sodium ions away from the salt crystal. In the image on the left, developed by Professor Angelos Michaelides, University College, London, you can see this. The green spheres are chlorine; the blue spheres are sodium.

In less polar alcohol, the alcohol molecules have no way to “grab” onto the sodium or chloride ions, which stay connected through ionic bonds, and don’t dissolve.

[q] EXPERIMENT 6: See if you can float a paper clip on the surface of a cup of water. Then see if you can do the same with alcohol. Here’s the procedure. If you don’t have the materials, read the procedure anyway, and try to predict what will happen in each case.

• Fill a cup with water. To make this easy, use a small cup (but one that’s big enough for a paper clip to float on the surface.
• Use a small paper clip. It’s easiest if you bend up a short metal handle from the paper clip so you can place the clip on the water as gently as possible. Bend it like this
• Gently place the paper clip on the surface of the water, then let go.
• Repeat the same step, except with alcohol in a cup instead of water.

Cg==Cg==Cg==

[Qq]

Here’s what’s happening.

Because water molecules are polar, they connect through hydrogen bonds. So imagine the paper clip floating on a web of water molecules (as shown in this image, which is ridiculously not drawn to scale). As long as the clip doesn’t break the web, it can float on top. The name for this web of water molecules on the surface of a body of water is surface tension.

Alcohol is much less polar than water. Because it’s non-polar, the molecules don’t form hydrogen bonds. Because they don’t form hydrogen bonds, the clips sink through the surface. Essentially, in the alcohol solution, there’s no surface tension (or, at least, not nearly enough to support a paper clip).

4. Additional points about water and hydrogen bonding

In the lab above, we addressed

• Surface tension
• Heat of vaporization
• Water’s ability to dissolve polar and ionic substances.

Here are a few more AP Bio-related concepts to know about related to water and hydrogen bonding.

4a. Frozen water has unique properties

Water has a relatively high freezing point . That’s because when water molecules get cool enough, they’ll grab onto one another through hydrogen bonding. Those bonds lock the molecules into the fixed, solid molecular matrix we know as ice. By contrast, isopropyl alcohol forms few hydrogen bonds and has to be cooled to -89 °C to become a solid. Methane (CH 4 ), which is completely nonpolar, has about the same molecular weight as water, but only liquifies at -182°C (and won’t solidify at all).

Water is less dense as a solid than as a liquid. As a result, ice floats on water. This is because when water freezes, the hydrogen bonds generate a crystal matrix in which the molecules are more spread out than when water is in a liquid form. This is a unique property: water might be the only substance whose solid form is less dense than its liquid form.

4b. Adhesion

Hydrogen bonding can lead to adhesion as well as cohesion. Adhesion is the molecular attraction between adjacent surfaces. Through hydrogen bonding, water can bond to other polar substances. This explains phenomena such as capillary action, in which water will flow into a narrow space such as a thin tube, even in opposition to the force of gravity. Adhesion between water molecules and the thin tubes in the stems of plants plays a major role in the process of transpiration, which is how plants move water from their roots up to their leaves.

4c. Specific Heat

Because of hydrogen bonding, water also has a very high specific heat : the amount of heat required to raise one gram of a substance by one degree C. Water has a high specific heat because the hydrogen bonds that form between water molecules constrain their movement. Since temperature is the average kinetic energy of the molecules within an object, that means that as you add heat to a body of water, there’s not a corresponding increase in the molecules’ kinetic energy. As a result, the temperature doesn’t rise.  One such watery body that resists wide temperature fluctuations is your body (or the body of any relatively large animal). Hydrogen bonds help keep the temperature within the body of any relatively large organism — on a molecular scale, that means anything the size of an earthworm or larger — relatively constant. It also keeps the Earth’s planetary temperature mild, because the oceans can absorb lots of heat without their temperature rising.

4d. Hydrogen bonding can occur between any two polar molecules.

For example, the two strands of DNA are held together by hydrogen bonds. These bonds are shown at number 6 in the image of DNA on the left below. On the right, you can see a closeup of the bonds between the nitrogenous bases that make up the central core of a DNA molecule. Note that the hydrogen bonds form between oxygen atoms and hydrogen atoms, or between nitrogen atoms and hydrogen atoms.

5. Video: Water Chemistry and Properties Part 2

6. Checking Understanding: Properties of Water

[qwiz random = “false” qrecord_id=”sciencemusicvideosMeister1961-Properties of Water F-I-B Quiz”]

[h]Properties of Water Quiz

[i]This quiz is a combination of the game “hangman” and a flashcard deck. With each question, you’ll type in the answer. If you get the question wrong, it goes back in the deck for you to repeat it.

[q] Water is a [hangman] molecule. As a result, water molecules form [hangman] bonds with one another.

[c]cG9sYXI=[Qq]

[c]aHlkcm9nZW4=[Qq]

[q]Whereas the [hangman] side of water has a partial positive charge, the [hangman] side of water has a partial negative charge

[c]b3h5Z2Vu[Qq]

[q]Because it has less [hangman] bonding, a drop of alcohol will have a much [hangman] shape than a drop of water. That’s because the bonds between water molecules create a lot of [hangman], a property that’s lacking in alcohol.

[c]ZmxhdHRlcg==[Qq]

[c]Y29oZXNpb24=[Qq]

[q]The amount of heat required to make a liquid into a gas is its heat of [hangman].

[c]dmFwb3JpemF0aW9u[Qq]

[q]Because it forms fewer [hangman] bonds, alcohol has a much [hangman] heat of vaporization than water.

[c]bG93ZXI=[Qq]

[q]Because water is polar, it’s great at dissolving [hangman] substances like salt and just about any [hangman] substance (such as sugar).

[c]aW9uaWM=[Qq]

[q]Because of hydrogen bonding, water has a lot of [hangman] [hangman], enabling a paper clip to float on the surface of a body of water.

[c]c3VyZmFjZQ==[Qq]

[c]dGVuc2lvbg==[Qq]

[q]Because of hydrogen bonding, water freezes at a relatively [hangman] temperature. In addition, hydrogen bonding makes ice [hangman] dense than water, causing ice to [hangman].

[c]aGlnaA==[Qq]

[c]bGVzcw==[Qq]

[c]ZmxvYXQ=[Qq]

[q]Whereas [hangman] involves attraction between water molecules (caused by hydrogen bonds), [hangman] involves hydrogen bonds forming between water molecules and another surface (such as the walls of the tubes that conduct water up the stem of a plant.

[c]YWRoZXNpb24=[Qq]

[q]The diagram below shows how [hangman] bonds can form between any two [hangman] molecules, and not just between water molecules.

[q] [hangman] heat is the amount of heat required to raise one gram of a substance by one degree C. Because of this property, bodies of water resist fluctuations in [hangman]. This has created a moderate climate on Earth owing to the role of the oceans as climate regulators.

[c]c3BlY2lmaWM=[Qq]

[c]dGVtcGVyYXR1cmU=[Qq]

[x][restart]

What’s next

• Proceed to Topic 1.1, Part 3: Acids, Bases, and the pH Scale (the next tutorial in AP Bio Unit 1)

• Virtual Labs

How To Extract DNA From Anything Living

First, you need to find something that contains DNA. Since DNA is the blueprint for life, everything living contains DNA.

For this experiment, we like to use green split peas. But there are lots of other DNA sources too, such as:

• Chicken liver
• Strawberries

Certain sources of DNA should not be used, such as:

• Your family pet, Fido the dog
• Your little sister's big toe
• Bugs you caught in the yard

Step 1: Blender Insanity!

Put in a blender:

• 1/2 cup of split peas (100ml)
• 1/8 teaspoon table salt (less than 1ml)
• 1 cup cold water (200ml)

Blend on high for 15 seconds.

The blender separates the pea cells from each other, so you now have a really thin pea-cell soup.

Step 2: Soapy Peas

Pour your thin pea-cell soup through a strainer into another container (like a measuring cup).

Add 2 tablespoons liquid detergent (about 30ml) and swirl to mix.

Let the mixture sit for 5-10 minutes.

Pour the mixture into test tubes or other small glass containers, each about 1/3 full.

Step 3: Enzyme Power

Add a pinch of enzymes to each test tube and stir gently. Be careful! If you stir too hard, you'll break up the DNA, making it harder to see.

Use meat tenderizer for enzymes. If you can't find tenderizer, try using pineapple juice or contact lens cleaning solution.

Step 4: Alcohol Separation

Tilt your test tube and slowly pour rubbing alcohol (70-95% isopropyl or ethyl alcohol) into the tube down the side so that it forms a layer on top of the pea mixture. Pour until you have about the same amount of alcohol in the tube as pea mixture.

Alcohol is less dense than water, so it floats on top. Look for clumps of white stringy stuff where the water and alcohol layers meet.

What is that Stringy Stuff?

DNA is a long, stringy molecule. The salt that you added in step one helps it stick together. So what you see are clumps of tangled DNA molecules!

DNA normally stays dissolved in water, but when salty DNA comes in contact with alcohol it becomes undissolved. This is called precipitation. The physical force of the DNA clumping together as it precipitates pulls more strands along with it as it rises into the alcohol.

You can use a wooden stick or a straw to collect the DNA. If you want to save your DNA, you can transfer it to a small container filled with alcohol.

You Have Just Completed DNA Extraction!

Now that you've successfully extracted DNA from one source, you're ready to experiment further. Try these ideas or some of your own:

Experiment with other DNA sources. Which source gives you the most DNA? How can you compare them?

Experiment with different soaps and detergents. Do powdered soaps work as well as liquid detergents? How about shampoo or body scrub?

Experiment with leaving out or changing steps. We've told you that you need each step, but is this true? Find out for yourself. Try leaving out a step or changing how much of each ingredient you use.

Do only living organisms contain DNA? Try extracting DNA from things that you think might not have DNA.

Frequently Asked Questions

Download a PDF version of this page

Blending separated the pea cells.

But each cell is surrounded by a sack (the cell membrane). DNA is found inside a second sack (the nucleus) within each cell.

To see the DNA, we have to break open these two sacks.

We do this with detergent.

Why detergent? How does detergent work?

Think about why you use soap to wash dishes or your hands. To remove grease and dirt, right?

Soap molecules and grease molecules are made of two parts:

Heads, which like water. Tails, which hate water.

Both soap and grease molecules organize themselves in bubbles (spheres) with their heads outside to face the water and their tails inside to hide from the water.

When soap comes close to grease, their similar structures cause them to combine, forming a greasy soapy ball.

A cell's membranes have two layers of lipid (fat) molecules with proteins going through them.

When detergent comes close to the cell, it captures the lipids and proteins.

After adding the detergent, what do you have in your pea soup?

In this experiment, meat tenderizer acts as an enzyme to cut proteins just like a pair of scissors.

The DNA in the nucleus of the cell is molded, folded, and protected by proteins.

The meat tenderizer cuts the proteins away from the DNA.

Trouble-shooting

1. I don't think I'm seeing DNA. What should I be looking for?

Look closely. Your DNA may be lingering between the two layers of alcohol and pea soup. Try to help the DNA rise to the top, alcohol layer. Dip a wooden stick into the pea soup and slowly pull upward into the alcohol layer. Also, look very closely at the alcohol layer for tiny bubbles. Even if your yield of DNA is low, clumps of DNA may be loosely attached to the bubbles.

2. What can I do to increase my yield of DNA?

Allow more time for each step to complete. Make sure to let the detergent sit for at least five minutes. If the cell and nuclear membranes are still intact, the DNA will be stuck in the bottom layer. Or, try letting the test tube of pea mixture and alcohol sit for 30-60 minutes. You may see more DNA precipitate into the alcohol layer over time.

Keep it cold. Using ice-cold water and ice-cold alcohol will increase your yield of DNA. The cold water protects the DNA by slowing down enzymes that can break it apart. The cold alcohol helps the DNA precipitate (solidify and appear) more quickly.

Make sure that you started with enough DNA. Many food sources of DNA, such as grapes, also contain a lot of water. If the blended cell soup is too watery, there won't be enough DNA to see. To fix this, go back to the first step and add less water. The cell soup should be opaque, meaning that you can't see through it.

Understanding the Science behind the Protocol

3. Why add salt? What is its purpose?

Salty water helps the DNA precipitate (solidify and appear) when alcohol is added.

4. Why is cold water better than warm water for extracting DNA?

Cold water helps keep the DNA intact during the extraction process. How? Cooling slows down enzymatic reactions. This protects DNA from enzymes that can destroy it.

Why would a cell contain enzymes that destroy DNA? These enzymes are present in the cell cytoplasm (not the nucleus) to destroy the DNA of viruses that may enter our cells and make us sick. A cell's DNA is usually protected from such enzymes (called DNases) by the nuclear membrane, but adding detergent destroys that membrane.

5. How is the cell wall of plant cells broken down?

It is broken down by the motion and physical force of the blender.

6. What enzyme is found in meat tenderizer?

The two most common enzymes used in meat tenderizer are Bromelain and Papain. These two enzymes are extracted from pineapple and papaya, respectively. They are both proteases, meaning they break apart proteins. Enzymatic cleaning solutions for contact lenses also contain proteases to remove protein build-up. These proteases include Subtilisin A (extracted from a bacteria) and Pancreatin (extracted from the pancreas gland of a hog).

7. How much pineapple juice or contact lens solution should I use to replace the meat tenderizer?

You just need a drop or two, because a little bit of enzyme will go a long way. Enzymes are fast and powerful!

8. Why does the DNA clump together?

DNA precipitates when in the presence of alcohol, which means it doesn't dissolve in alcohol. This causes the DNA to clump together when there is a lot of it. And, usually, cells contain a lot of it!

For example, each cell in the human body contains 46 chromosomes (or 46 DNA molecules). If you lined up those DNA molecules end to end, a single cell would contain six feet of DNA! If the human body is made of about 100 trillion cells, each of which contains six feet of DNA, our bodies contain more than a billion miles of DNA!

9. How can we confirm the white, stringy stuff is DNA?

There is a protocol that would allow you to stain nucleic acids, but the chemical used would need to be handled by a teacher or an adult. So, for now, you'll just have to trust that the molecules precipitating in the alcohol are nucleic acids.

10. Isn't the white, stringy stuff actually a mix of DNA and RNA?

That's exactly right! The procedure for DNA extraction is really a procedure for nucleic acid extraction.

11. How long will my DNA last? Will it eventually degrade and disappear?

Your DNA may last for years if you store it in alcohol in a tightly-sealed container. If it is shaken, the DNA strands will break into smaller pieces, making the DNA harder to see. If it disappears it's likely because enzymes are still present that are breaking apart the DNA in your sample.

Using more sophisticated chemicals in a lab, it is possible to obtain a sample of DNA that is very pure. DNA purified in this way is actually quite stable and will remain intact for months or years.

Comparing the DNA Extracted from Different Cell Types

12. Does chromosome number noticeably affect the mass of DNA you'll see?

Cells with more chromosomes contain relatively more DNA, but the difference will not likely be noticeable to the eye. The amount of DNA you will see depends more on the ratio of DNA to cell volume.

For example, plant seeds yield a lot of DNA because they have very little water in the cell cytoplasm. That is, they have a small volume. So the DNA is relatively concentrated. You don't have to use very many seeds to get a lot of DNA!

13. Why are peas used in this experiment? Are they the best source of DNA?

Peas are a good source of DNA because they are a seed. But, we also chose the pea for historical reasons. Gregor Mendel, the father of genetics, did his first experiments with the pea plant.

14. How does the experiment compare when using animal cells instead of plant cells?

The DNA molecule is structurally the same in all living things, including plants and animals. That being said, the product obtained from this extraction protocol may look slightly different depending on whether it was extracted from a plant or an animal. For example, you may have more contaminants (proteins, carbohydrates) causing the DNA to appear less string-like, or the amount of DNA that precipitates may vary.

15. What sources might I use to extract DNA from animal cells?

Good sources for animal cells include chicken liver, calf thymus, meats and eggs (from chicken or fish).

16. Why do peas require meat tenderizer, but wheat germ does not?

We at the GSLC have done a fair amount of testing with the split pea protocol and the wheat germ protocol. We have found no difference in the "product" (nucleic acids) that is observable, whether using meat tenderizer or not. So, the step was left out of the wheat germ protocol, but kept in the split pea protocol just for fun.

Even though it's not necessary, it may be doing something we can't see. For example, perhaps by using the meat tenderizer you get a purer sample of DNA, with less protein contaminating the sample.

Real-life Applications of the Science of DNA Extraction

17. Can you extract human DNA using this protocol?

Yes, in theory. The same basic materials are required, but the protocol would need to be scaled down (using smaller volumes of water, soap and alcohol). This is because you're not likely starting the protocol with the required amount—1/2 cup—of human cells! That means that you will not extract an amount of DNA large enough to visualize with the naked eye. If you wanted to see it, you would need a centrifuge to spin down (to the bottom of the tube) the small amount of DNA present in the sample.

18. What can be done with my extracted DNA?

This sample could be used for gel electrophoresis, for example, but all you will see is a smear. The DNA you have extracted is genomic, meaning that you have the entire collection of DNA from each cell. Unless you cut the DNA with restriction enzymes, it is too long and stringy to move through the pores of the gel.

A scientist with a lab purified sample of genomic DNA might also try to sequence it or use it to perform a PCR reaction. But, your sample is likely not pure enough for these experiments to really work.

19. How is DNA extraction useful to scientists? When do they use such a protocol, and why is it important?

The extraction of DNA from a cell is often a first step for scientists who need to obtain and study a gene. The total cell DNA is used as a pattern to make copies (called clones) of a particular gene. These copies can then be separated away from the total cell DNA, and used to study the function of that individual gene.

Once the gene has been studied, genomic DNA taken from a person might be used to diagnose him or her with a genetic disease. Alternatively, genomic DNA might be used to mass produce a gene or protein important for treating a disease. This last application requires techniques that are referred to as recombinant DNA technology or genetic engineering.

20. Can I use a microscope to see the DNA that I extract?

Unfortunately, a microscope will not allow you to see the double helical structure of the DNA molecule. You'll only see a massive mess of many, many DNA molecules clumped together. In fact, the width of the DNA double helix is approximately one billionth of a meter! This is much too small to see, even with the most powerful microscope. Instead, a technique called X-ray crystallography can be used to produce a picture of the DNA molecule. It was by looking at such a picture (taken by Rosalind Franklin) that James Watson and Francis Crick were able to figure out what the DNA molecule looks like.

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The ‘whoosh’ bottle demonstration

In association with Nuffield Foundation

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A mixture of alcohol and air in a large polycarbonate bottle is ignited. The resulting rapid combustion reaction, often accompanied by a dramatic ‘whoosh’ sound and flames, demonstrates the large amount of chemical energy released in the combustion of alcohols

This demonstration requires careful preparation and is the subject of a supplementary risk assessment by CLEAPSS,  SRA006 . Schools are advised not to deviate from the details described in this risk assessment. If any variation is necessary, members should contact CLEAPSS for preparing a special risk assessment. Teachers should also, of course, consult their own employer’s risk assessment.

A single demonstration will take 5–10 minutes. Repeat demonstrations will require either the drying out of the reaction vessel used for the first demonstration or spare dry reaction vessels.

• Reaction vessel, 1 or more (note 1)
• Rubber stopper or plastic cap (to fit the reaction vessel)
• Beaker (250 cm 3 ), 1 for each alcohol used
• Wooden splints, as needed (note 2)

Apparatus notes

• The reaction vessel consists of a large polycarbonate bottle, as used in workplace water dispensers. These have a volume of 16–20 dm 3 . A clean, dry bottle is required for each demonstration. It takes time to clean and dry once it has been used for a demonstration. For this reason, up to 4 bottles may be required. The bottle must be made of polycarbonate (marked PC) and of no other material. If using empty but wet water cooler containers, stand them inverted to allow any remaining water to drain and then leave upright for several days until completely dry.
• Attach a wooden splint to the end of the meter rule or stick using adhesive tape, angling the splint so that when the meter rule is horizontal, the splint is sloping downwards. Provide a lighter or matches well away from the alcohol bottles.

One or more of the following alcohols, 40 cm 3  of each one used:

• Methanol (HIGHLY FLAMMABLE, TOXIC)
• Ethanol (IDA, or Industrial Denatured Alcohol) (HIGHLY FLAMMABLE, HARMFUL)
• Propan-1-ol (HIGHLY FLAMMABLE, IRRITANT)
• Propan-2-ol (HIGHLY FLAMMABLE, IRRITANT)

Health, safety and technical notes

• Read our standard health and safety guidance
• Both demonstrator and class should be wearing eye protection. Select a safe, level place for the demonstration, with at least 2.5 m clearance above the top of the vessel to the ceiling above, and no flammable materials above it. If the laboratory bench does not allow for this, four stable laboratory stools supporting a large wooden tray may give sufficient clearance and stability. Set out the bottles containing the alcohols and the beakers at least 1 m away from the demonstration. No flames within 1 m. Students at least 4 m away.
• Methanol, CH 3 OH(l), (HIGHLY FLAMMABLE, TOXIC) – see CLEAPSS Hazcard HC040b .
• Ethanol (IDA, Industrial Denatured Alcohol), CH 3 CH 2 OH(l), (HIGHLY FLAMMABLE, HARMFUL) – see CLEAPSS Hazcard HC040a . 
• Propan-1-ol, CH 3 CH 2 CH 2 OH(l), (HIGHLY FLAMMABLE, IRRITANT) – see CLEAPSS Hazcard HC084a . 
• Propan-2-ol, CH 3 CHOHCH 3 (l), (HIGHLY FLAMMABLE, IRRITANT) – see CLEAPSS Hazcard HC084a . 
• Pour about 40 cm 3  of the selected alcohol into a beaker and then transfer into the reaction vessel.
• Insert the rubber stopper and roll the reaction vessel on its side for 10 seconds, to and fro, allowing the alcohol to vaporise and the vapour to fill the vessel. Do not warm the alcohol.
• Pour surplus liquid alcohol back into the beaker, draining the vessel as completely as possible, and move the beaker back to the rest of the alcohol stock, away from any risk of catching fire. Surplus liquid left in the vessel may ignite and set fire to the vessel as well.
• Stand the reaction vessel securely inside the safety screens and remove the stopper. Light the wooden splint, and apply the lighted end of the splint to the open neck of the vessel. Do not lean over the screens to apply the ignition. It is dangerous to ignite by dropping a lighted match into the vessel when using ethanol or methanol. For both propanols, this method may be used providing the neck of the bottle is above head height.
• The alcohol vapour should ignite with a loud ‘whoosh’, with flames shooting out of the top of the vessel.

Teaching notes

The experiment demonstrates dramatically just how much chemical energy is released from such a small quantity of fuel.

The flame colour varies with the proportion of carbon in the alcohol molecule. With methanol and ethanol there is a very quick ‘whoosh’ sound and a blue flame shoots out of the bottle. With propan-1-ol and propan-2-ol, the sound is similar but the reaction is slightly slower, easier to observe, and blue and yellow flames may be observed ‘dancing’ in the bottle. The presence of water reduces the likelihood of dancing flames.

Additional information

This is a resource from the  Practical Chemistry project , developed by the Nuffield Foundation and the Royal Society of Chemistry.

Practical Chemistry activities accompany  Practical Physics  and  Practical Biology . 

The experiment is also part of the Royal Society of Chemistry’s Continuing Professional Development course:  Chemistry for non-specialists . 

© Nuffield Foundation and the Royal Society of Chemistry

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Specification

• Enthalpy change (ΔH) is the heat energy change measured under conditions of constant pressure.
• a) explanation that some chemical reactions are accompanied by enthalpy changes that are exothermic (ΔH, negative) or endothermic (ΔH, positive)
• An exothermic reaction is one that transfers energy to the surroundings so the temperature of the surroundings increases. Exothermic reactions include combustion, many oxidation reactions and neutralisation. Everyday uses of exothermic reactions include…
• Distinguish between endothermic and exothermic reactions on the basis of the temperature change of the surroundings.
• 7.10 Describe an exothermic change or reaction as one in which heat energy is given out
• C1.2.1 distinguish between endothermic and exothermic reactions on the basis of the temperature change of the surroundings
• C3.2a distinguish between endothermic and exothermic reactions on the basis of the temperature change of the surroundings
• In combustion, a substance reacts with oxygen releasing energy.
• Hydrocarbons and alcohols burn in a plentiful supply of oxygen to produce carbon dioxide and water.
• 2.5.22 describe the complete and incomplete combustion of alcohols;
• 2.5.21 describe the complete and incomplete combustion of alcohols;
• 2.6.4 describe the complete and incomplete combustion of alcohols and their use as an alternative fuel;

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Testing isopropyl alcohol purity

I'm curious how to test purity of isopropyl alcohol? I simply got very curious today. I bought rubbing alcohol and it doesn't say what's the purity anywhere. It could be 70%, but it could also be 90%, or 99% or even 99.9%. I'm a curious man so I started googling but couldn't find anything.

If I were a chemist, how would I test the purity?

• organic-chemistry
• experimental-chemistry

• $\begingroup$ If you have chemistry equipment ready, then you would use a gas chromatograph ( wiki-link ). With household items is far more difficult, I cannot think of an accurate way, hence the comment ;) $\endgroup$ –  Eljee Commented Mar 10, 2015 at 13:41
• $\begingroup$ I just had an idea myself - since impure isopropyl would contain water, if I took 10 grams of isopropyl and somehow measured how much water there is, then I could tell its purity. For example if there were 3 grams of water, then it would be 70% pure. $\endgroup$ –  bodacydo Commented Mar 10, 2015 at 13:49
• $\begingroup$ True, though that only works under the assumption that the only impurity is water. Might it also be ethanol, or methanol? Other hydrocarbons? $\endgroup$ –  Eljee Commented Mar 10, 2015 at 13:50
• $\begingroup$ You're right. I didnt think of that. $\endgroup$ –  bodacydo Commented Mar 10, 2015 at 13:55
• $\begingroup$ If I were a chemist I would use the USP monograph for IPA, which involves a GC fitted with a TCD. No need for a NMR/MS $\endgroup$ –  Saccades Commented Feb 16, 2017 at 17:08

5 Answers 5

If the isopropanol mixture was bought commercially, the chances that it contains significant amounts of methanol or ethanol are fairly small, I think. (I've never seen commercial isopropanol in the US that contains > 3% of these impurities, at least, but the situation may vary in other countries or markets.)

If you can assume that the only other main component is water, the easiest way to estimate purity is simply by measuring the density. 100% pure isopropanol has a density at 20 °C of 0.786 g per mL. Pure water has a density of 1.00 g/mL. At intermediate concentrations of isopropanol, the density is in between those values. If you can accurately measure both (a) the volume and (b) the weight of a portion of isopropanol, you should be able to measure the density. I know my kitchen scale and kitchen measuring cups would be precise enough for this.

If you can't assume that water is the only other impurity, other methods such as NMR, chromatography, or spectroscopy would probably be required. I think NMR would probably be the most informative (but perhaps the least accessible to the home chemist.)

• 1 $\begingroup$ Very good answer. Thanks. I think I can use archimede's law to figure out density at room temperature? $\endgroup$ –  bodacydo Commented Mar 10, 2015 at 21:18
• 1 $\begingroup$ Yes, if you use a completely sealed container and are willing to neglect the weight and volume of the container. $\endgroup$ –  Curt F. Commented Mar 10, 2015 at 21:39

If you really want to figure what the “purity” Or rather the volume of isopropyl to water by weight aka $70\%$ , $91\%$ . And you don’t have a gas chromatograph, this is about the closest your going to get to an accurate Volumetric representation.

This is a fractional distillation column same basic principle as distilling drinking alcohol but much different equipment and processes. However using this column you are able to precisely control the temperature of the liquid or in this case the isopropyl alcohol in the heating mantle and allow it to evaporate and be distilled and collect after passing through a water jacket to condense the vapor and as long as you monitor the temperature at the neck located at the very top where the vertical column branches off to the right and have a thermometer right at that joint and maintain a temperature of $\pu{80 ^{\circ}C}$ ( $\pu{176 ^{\circ}F}$ ) and let the isopropyl evaporate. Once the temperature begins to rise above $\pu{80 ^{\circ}C}$ ( $\pu{176 ^{\circ}F}$ ) to $\pu{82 ^{\circ}C}$ ( $\pu{180 ^{\circ}F}$ ) or higher, you stop the heat and remove the distillate container. Once everything has cooled down, you can measure what is remaking in the first Vessel and the distillate vessel. And with a bit of a margin for error using the original volume used, in my case for this rig I used I was using 70% and a starting volume of $\pu{500 ml}$ . So my resulting measurements were, distillate - $\pu{347 ml}$ , undistilled liquid - $\pu{148 ml}$ . Resulting in a total volume of $\pu{495 ml}$ with a distillate percentage of $70.10\%$ (isopropyl) and remaining liquid (water) percentage $29.89\%$ .

I hope this helps!!!

• $\begingroup$ Other things beside, just from a mechanical perspective, this setup relies too much on the single supporting bar on the left (one clamp only?), behind the column, and the Erlenmeyer flask on the right (high centre of gravity). It does not allow a quick exchange of the receiver flask without demanding a lot to the joints and Keck rings supporting the Liebig condensers, nor quick removal of the heat if needed without compromising the stand. The garden-hose like click connector between the hoses still to clamp is a nice thing, though. And keep the bench below the medical cabinet clean. $\endgroup$ –  Buttonwood Commented Jun 26, 2020 at 9:45

Dissolve non iodine table salt into a known amount and let it sit, measure the amount of water that sits in the bottom compared to the amount of alcohol that is in the top after about 10-15 minutes of sitting. You can then extrapolate what percentage of alcohol you bought. Example would be about half water and half alcohol if you got 50% isopropyl alcohol.

• $\begingroup$ I guess you mean that the salt won't disolve in alcohol, right? But how do you distinguish the salty water from alcohol? The salt won't change water color, right? (If so they will be both transparent like water). $\endgroup$ –  JinSnow Commented Dec 6, 2020 at 16:28
• $\begingroup$ I did the test following youtube video, alcohol will be clear layer above murky salt water. But I (almost) didn't see the alcohol layer. I'm using table salt (no iodine smell as I know, but not sure), and sit the mixture for an hour without change. I even drop stamp ink hoping the ink will be dissolved by alcohol nonpolar and not by salt water (the ink just drop directly to salt water layer and keep the ball shape, no ink dissolved on alcohol layer). So that means the alcohol content is very low? $\endgroup$ –  RainerJ Commented Dec 18, 2020 at 11:23

For very quick test, you can go for flame test. Pure IPA when poured on a cotton burns upto a certain flame length . when impurities are added , the length of flame decreases. Do not forget to keep the size of cotton same while comparing

• 3 $\begingroup$ This doesn't help you to assess the purity unless you have a sample of known purity to compare to. And it doesn't seem very precise anyway. $\endgroup$ –  bon Commented May 30, 2018 at 9:24

Simple method is measure 100 ml Isopropyl alcohol water mixture heat at 80 degrees centigrade and after distilling left of liquid,cool and measure the volume. You get water content and the balance quantity is IPA.///

• 1 $\begingroup$ Even if you were able to separate two compounds with a difference in boiling temperature of 20 degrees Celsius with a column (bp water 100, bp isopropanol 82.6 Celsius) this answer does not account for the azeotropic mixture with 91 vol% of IPA distilling over at about 80 Celsius and atmospheric pressure. So no, there is no sudden stop of the distillation with pure water left in the roundbottom flask. $\endgroup$ –  Buttonwood Commented Jun 26, 2020 at 9:21

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