experiments on rate of reaction

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Investigating The Rate of a Reaction ( Cambridge (CIE) IGCSE Chemistry )

Revision note.

Investigating the rate of a reaction

To measure the  rate of a reaction , we need to be able to measure:

How quickly the reactants are used up OR How quickly the products are formed

The method used for measuring depends on the substances involved

There are a number of ways to measure a reaction rate in the lab

They all depend on a property changing during the course of the reaction

Properties that change during the course of a reaction include:

The changing property is taken to be proportional to the concentration of the reactant or product

Faster reactions can be easier to measure when the reaction is over

This can be done by averaging a collected measurement over the course of the reaction

Some reaction rates can be measured as the reaction proceeds (this generates more data)

Three commonly used techniques are:

measuring mass loss on a balance

measuring the volume of a gas produced

measuring a reaction where there is a colour change at the end of the reaction

Investigating the effect of concentration of a solution on the rate of reaction

Diagram showing the apparatus needed to investigate the effect of concentration on the rate of reaction

Measure 50 cm 3 of sodium thiosulfate solution into a flask

Measure 5 cm 3 of dilute hydrochloric acid into a measuring cylinder

Draw a cross on a piece of paper and put it underneath the flask

Add the acid into the flask and immediately start the stopwatch

Look down at the cross from above and stop the stopwatch when the cross can no longer be seen

Repeat using different concentrations of sodium thiosulfate solution (mix different volumes of sodium thiosulfate solution with water to dilute it)

With an increase in the concentration of a solution, the rate of reaction will increase

This is because there will be more reactant particles in a given volume, allowing more frequent and successful collisions, increasing the rate of reaction

Investigating the effect of surface area on the rate of reaction 

Diagram showing the process of downwards displacement to investigate the effect of the surface area of a solid on the rate of reaction

Add dilute hydrochloric acid into a conical flask

Use a delivery tube to connect this flask to a measuring cylinder upside down in a bucket of water (downwards displacement)

Add magnesium ribbon to the conical flask and quickly put the bung back into the flask

Measure the volume of gas produced in a fixed time using the measuring cylinder

Repeat with different size pieces of magnesium ribbon

The same total mass of magnesium must be used 

Smaller pieces of magnesium ribbon cause an increase in the surface area of the solid, so the rate of reaction will increase

This is because more surface area of the particles will be exposed to the other reactant so there will be more frequent and successful collisions, increasing the rate of reaction

Investigating the effect of temperature on the rate of reaction

Diagram showing the apparatus needed to investigate the effect of temperature on the rate of reaction

Dilute hydrochloric acid is heated to a set temperature using a water bath

Add the dilute hydrochloric acid into a conical flask

Add a strip of magnesium and start the stopwatch

Stop the time when the magnesium fully reacts and disappears

Repeat at different temperatures and compare results

With an increase in the temperature, the rate of reaction will increase

This is because the particles will have more kinetic energy than the required activation energy, therefore more frequent and successful collisions will occur, increasing the rate of reaction

Investigating the effect of a catalyst on the rate of reaction

Diagram showing the apparatus needed to investigate the effect of a catalyst on the rate of reaction

Add hydrogen peroxide into a conical flask

Use a delivery tube to connect this flask to a measuring cylinder upside down in a tub of water (downwards displacement)

Add the catalyst manganese(IV) oxide into the conical flask and quickly place the bung into the flask

Repeat experiment without the catalyst of manganese(IV) oxide and compare results

Using a catalyst will increase the rate of reaction

The catalyst will provide an alternative pathway requiring lower activation energy so more colliding particles will have the necessary activation energy to react

This will allow more frequent and successful collisions, increasing the rate of reaction

Monitoring changes in mass

Many reactions involve the production of a gas which will be released during the reaction

The gas can be collected and the volume of gas monitored as per some methods above

Alternatively, the reaction can be performed in an  open flask  on a balance to measure the loss in mass of reactant

Cotton wool is usually placed in the mouth of the flask which allows gas out but prevents any materials from being ejected from the flask (if the reaction is vigorous)

Diagram showing the set-up for measuring the rate of reaction by loss in mass

This method is not suitable for hydrogen and other gases with a small relative formula mass,  M r  as the loss in mass may be too small to measure

Examiner Tip

There are many different methods of investigating the rate of reaction.

Another method of gas collection you may see uses a gas syringe.

Extended tier students may be required to devise and evaluate methods of investigating rates of reaction.

Evaluating investigations of rates of reactions

Extended tier only

When investigating rates of reaction, there are a number of different methods that can be used to carry out the same investigation

Evaluating what is the best method to use is part of good experimental planning and design

This means appreciating some of the advantages and disadvantages of the methods available

Advantages and disadvantages of methods of investigating rates of reaction

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• Chemical Change & Rate of Reaction
• Reversible Reactions & Equilibrium
• The Characteristic Properties of Acids & Bases
• Preparation of Salts
• The Periodic Table & Trends
• Group Properties & Trends
• Properties, Uses & Alloys of Metals
• Reactivity Series & Corrosion of Metals
• Extraction of Metals

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Alka Seltzer Reaction Rate Experiment

Ready to race with this  Alka Seltzer Reaction Rate Experiment?  In this fun and quick science experiment , you’ll see which Alka-Seltzer tablet dissolves the fastest in water! It’s a fantastic way to explore how temperature affects chemical reactions . Grab your stopwatch, and let’s get started!

Chemical reactions happen all around us every day, from baking cookies to rusting metal. One important factor that can change how fast a reaction occurs is temperature. In this experiment, you’ll discover how different water temperatures affect the dissolving rate of Alka-Seltzer tablets. This is a great introduction to the concepts of solubility and chemical reactions.

💡Explore more chemical changes (chemical reactions) here.

Grade Level Recommendation:  This experiment is perfect for students in grades 2-5, but younger kids can join with adult supervision.

• Several clear cups or jars
• Water (cold tap water, room temperature tap water, hot tap water)
• Alka-Seltzer tablets
• Thermometer (optional)
• Stopwatch or timer
• Notepad and pencil for observations (printable pages below)

Set Up Alka Seltzer Reaction Rate Experiment

Prepare the Water : Gather three clear cups or jars and fill each with water. Ensure each cup has the same amount of water at a different temperature: one with cold water, one with room-temperature water, and one with hot water (🛑 Adult assistance is highly suggested).

Get Ready to Race : Open three Alka-Seltzer tablets and have them ready to drop into the cups simultaneously.

Start the Experiment : Drop a whole tablet into each cup simultaneously and start your timer.

Observe : Watch closely and note how quickly each tablet dissolves at different water temperatures.

Record Your Observations : Write down how long it takes for each tablet to fully dissolve in each cup.

Alka Seltzer Experiment Variables

• Temperature of the water (e.g., cold, room temperature, hot)
• Size of the Alka-Seltzer tablet (whole, half, crushed)
• Amount of water used
• Dependent Variable : This is the variable that you measure, which in this case would be the  reaction rate  or  time it takes for the Alka-Seltzer tablet to completely dissolve .

Science Explanation:

When the Alka-Seltzer tablet dissolves, one of the ingredients, called  sodium bicarbonate , breaks apart into smaller pieces, including  bicarbonate ions . These bicarbonate ions mix with  hydrogen ions  from the  citric acid  in the tablet. 

When they react, they create  carbon dioxide gas  (which makes the bubbles) and  water . The  rate of a chemical reaction  depends on things like water temperature or how the tablet is broken up. The faster the reaction happens, the quicker the bubbles form, which is why the tablet fizzes at different speeds!

Temperature affects the rate of a reaction . When water is heated, its molecules move faster. Faster-moving molecules cause the tablet to break down more quickly, speeding up the chemical reaction. That’s why the tablet dissolves faster in hot water than in cold water. In scientific terms, increasing temperature speeds up the reaction rate, which is a principle that applies to many chemical reactions.

Applying the Scientific Method:

💡This is a fantastic  science fair project  for kids. Kids can explore   variables   and the  scientific method .

• Question : How does the water temperature affect the dissolving rate of Alka-Seltzer tablets?
• Hypothesis : If the water is warmer, then the Alka-Seltzer tablet will dissolve faster.
• Experiment : Use cups of water at different temperatures (cold, room temperature, and hot) and measure the dissolving times of the tablets.
• Observation : Note the time it takes for each tablet to dissolve.
• Conclusion : Compare the times to see which water temperature resulted in the fastest dissolving tablet.

Free Printable Journal Pages

Extension Activities:

• Try Different Temperatures : What happens when using water with ice cubes versus boiling water? Add more temperature variations to explore the relationship further.
• Tablet Size : Break the Alka-Seltzer tablets into smaller pieces. Does size affect the dissolving rate in different temperatures?
• Stirring : Stir the water while the tablet dissolves. How does stirring impact the dissolving rate? Does the effect differ based on water temperature?

Related Science Activities:

• Temperature and Solubility : Use sugar or salt instead of Alka-Seltzer tablets and observe how temperature affects their dissolving rates in water.
• Fizzing Science : Experiment with vinegar and baking soda to observe how temperature changes the fizzing reaction.
• Pop Rocks Experiment : Drop Pop Rocks into different temperatures of soda and see how quickly they pop, relating it back to temperature and gas production.

Helpful Science Resources

Here are a few resources that will help you introduce science more effectively to your kids or students and feel confident presenting materials. You’ll find helpful free printables throughout.

• Printable Science Project Pack
• Best Science Practices (as it relates to the scientific method)
• Science Vocabulary
• All About Scientists
• Free Science Worksheets
• DIY Science Kits
• Science Tools for Kids
• Scientific Method for Kids
• Citizen Science Guide
• Join us in the Club

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The effect of concentration on reaction rate

• Four out of five

Start your stopwatches, and get ready to learn about reaction rates. Mixing different solutions of sodium thiosulfate with an acid will result in sulfur precipitate forming at different speeds. Will students keep track?

Create a lesson of discovery where students put their knowledge of concentrations and reactions into practical use. This experiment uses simple chemicals and equipment found in your learning space. 

This experiment should take 60 minutes.

• Eye protection
• Conical flask, 250 cm 3
• Measuring cylinder, 100 cm 3
• Sodium thiosulfate solution 50 g dm –3
• Hydrochloric acid 2 mol dm –3

Health, safety and technical notes

• Read our standard health and safety guidance . 
• Always wear eye protection.
• Sodium thiosulfate solution 50 g dm –3 is low hazard (see CLEAPPS Hazcard HC095a ).
• Dilute hydrochloric acid is low hazard at the concentration used (see CLEAPSS Hazcard HC057a ).
• Put 50 cm 3 of sodium thiosulfate solution in a flask.
• Measure 5 cm 3 of dilute hydrochloric acid in a small measuring cylinder.
• Add the acid to the flask and immediately start the clock. Swirl the flask to mix the solutions and place it on a piece of paper marked with a cross.
• Look down at the cross from above. When the cross disappears, stop the clock and note the time. Record this in the table provided on the student sheet.
• Repeat this using different concentrations of sodium thiosulfate solution. Make up 50 cm 3 of each solution. Mix different volumes of the sodium thiosulfate solution with water as shown in the table.
• As soon as possible, pour the solution down the sink (in the fume cupboard if possible) and wash away.
• Calculate the concentration of sodium thiosulfate in the flask at the start of each experiment. Record the results in the table provided on the student sheet.
• For each set of results, calculate the value of 1/time. (This value can be taken as a measure of the rate of reaction).
• Plot a graph of 1/time taken on the vertical (y) axis and concentration on the horizontal (x) axis.
• Sulfur dioxide (a toxic gas) forms as a by-product. Ensure good ventilation. If there are asthmatics in the class, the risk assessment should take this into account and necessary adjustments made, such as working in a fume cupboard, reducing the scale etc.
• As soon as the reaction is complete, pour the solutions away, preferably into the fume cupboard sink. Wash away with plenty of water.
• A light sensor can be used to monitor the precipitation on a computer. The result, in the form of graphs on the computer, can be analysed using data logging software.
• A light sensor clamped against a plastic cuvette filled with the reactants substitutes for a colorimeter. The data logging software shows the turbidity on a graph, and this tends to yield more detail than the standard end-point approach. The rate of change can be measured using the slope of the graph or the time taken for a change to occur.

More resources

Add context and inspire your learners with our short career videos showing how chemistry is making a difference .

The effect of concentration on reaction rate – student sheet

The effect of concentration on reaction rate – teacher notes, additional information.

This practical is part of our  Chemistry for Non-Specialists collection . This experiment has been adapted from Classic Chemistry Demonstrations, Royal Society of Chemistry, London, p.162-164

• 14-16 years
• 16-18 years
• Practical experiments
• Reactions and synthesis
• Rates of reaction

Specification

• AT.5 Making and recording of appropriate observations during chemical reactions including changes in temperature and the measurement of rates of reaction by a variety of methods such as production of gas and colour change.
• 5 Investigate how changes in concentration affect the rates of reactions by a method involving measuring the volume of a gas produced and a method involving a change in colour or turbidity. This should be an investigation involving developing a hypothesi…
• Factors which affect the rates of chemical reactions include: the concentrations of reactants in solution, the pressure of reacting gases, the surface area of solid reactants, the temperature and the presence of catalysts.
• Students should be able to recall how changing these factors affects the rate of chemical reactions.
• RP19 Investigation of how changes in concentration affect the rates of reactions by a method involving measuring the volume of a gas produced and a method involving a change in colour or turbidity. This should be an investigation involving developing…
• Explain the effects on rates of reaction of changes in temperature, concentration and pressure in terms of the frequency and energy of collision between particles.
• Describe the effect of changes in temperature, concentration, pressure, and surface area on rate of reaction.
• 11 Investigate how changes in concentration affect the rates of reactions by a method involving measuring the volume of a gas produced and a method involving a change in colour or turbidity. This should be an investigation involving developing…
• 5 Making and recording of appropriate observations during chemical reactions including changes in temperature and the measurement of rates of reaction by a variety of methods such as production of gas and colour change
• 7.1b observing a colour change (in the reaction between sodium thiosulfate and hydrochloric acid)
• 7.4 Explain the effects on rates of reaction of changes in temperature, concentration, surface area to volume ratio of a solid and pressure (on reactions involving gases) in terms of frequency and/or energy of collisions between particles
• 8 Investigation the effect of surface area, concentration and temperature on the rate of a chemical reaction
• Making and recording of appropriate observations during chemical reactions including changes in temperature and the measurement of rates of reaction by a variety of methods such as production of gas and colour change
• C6.2.1 describe the effect on rate of reaction of changes in temperature, concentration, pressure, and surface area
• C6.2.2 explain the effects on rates of reaction of changes in temperature, concentration and pressure in terms of frequency and energy of collision between particles
• C5 Investigation the effect of surface area, concentration and temperature on the rate of a chemical reaction
• C5.1c describe the effect of changes in temperature, concentration, pressure, and surface area on rate of reaction
• C5.1d explain the effects on rates of reaction of changes in temperature, concentration and pressure in terms of frequency and energy of collision between particles
• C5.2c describe the effect of changes in temperature, concentration, pressure, and surface area on rate of reaction
• C5.2d explain the effects on rates of reaction of changes in temperature, concentration and pressure in terms of frequency and energy of collision between particles
• concentration
• by increasing the concentration of a reactant
• (b) the effect of changes in temperature, concentration (pressure) and surface area on rate of reaction
• Use of: graduated glassware (volume) such as measuring cylinders of varying sizes;
• Use of: stopclock or stopwatch (time);
• 2.3.1 demonstrate knowledge and understanding that the rate of a reaction may be determined by measuring the loss of a reactant or gain of a product over time and use the equation: rate = 1 / time
• 2.3.2 suggest appropriate practical methods to measure the rate of a reaction and collect reliable data (methods limited to measuring a change in mass, gas volume or formation of a precipitate against time) for the reaction of: metals with dilute acid;…
• 2.3.3 interpret experimental data quantitatively, for example drawing and interpreting appropriate graphs to determine the rate of reaction; and
• 2.3.2 suggest appropriate practical methods to measure the rate of a reaction and collect reliable data (methods limited to measuring a change in mass, gas volume or formation of a precipitate against time) for the reaction of: metals with dilute acid…
• Rate of reaction.
• Concentration. Particle size.
• Mandatory experiment 6.2 - Studying the effects on the reaction rate of (i) concentration and (ii) temperature, using sodium thiosulfate solution and hydrochloric acid

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