carbohydrates experiment in biochemistry lab report

Academia.edu no longer supports Internet Explorer.

To browse Academia.edu and the wider internet faster and more securely, please take a few seconds to  upgrade your browser .

Enter the email address you signed up with and we'll email you a reset link.

• We're Hiring!
• Help Center

Download Free PDF

Experiment 6: Qualitative test of carbohydrates

Related papers

This experiment aims to introduce you with the identification of unknown carbohydrates. The test samples were 1% Dextrin, 1% Galactose, 1% Glucose, 1% Lactose, 1% Sucrose, 1% Maltose and 1% Starch. The test solutions in the Molisch test were treated with Molisch reagent and concentrated sulfuric acid. In the Orcinol test, test solutions were added with Bial’s reagent and was heated in a flame. For the Seliwanoff’s test, the test solutions were added with Seliwanoff’s reagent and was heated in a water bath. And for the Barfoed’s and Benedict’s tests, the test solutions were added with the reagent. Heated in water bath. In Barfoed’s test, the time was recorded when precipitate forms. Thus, the postive result for Molisch test is purple liquid layer. In the Orcinol’s test the positive result for pentoses is blue or green color and hexoses is yellow or brown color. For Seliwanoff’s test, the postive result is red product. Lastly, for Barfoed’s and Benedicts test were the presence of brick red precipitate.

The contemporary chemistry teaching laboratories endeavour to integrate the current themes of safety, sustainability and simplicity in all aspects of experimental design. The qualitative analysis of carbohydrates is central to study of organic chemistry and biochemistry laboratory courses at undergraduate level. This paper presents a novel qualitative test for detection of carbohydrates using a single reagent, alkaline potassium hexacyanoferrate (III). This reagent shows a characteristic behaviour towards carbohydrates. The observation is developed and presented as a simple, safe and easy to perform test for detection of carbohydrates. The test is suitable for micro scale as well as mini scale quantities. It involves no special technique to perform, is quick to accomplish and gives unambiguous results. These attributes make it suitable to be adopted in teaching laboratories.

Post Experiment Questions: 1) Enumerate at least five (5) qualitative tests used for detection of a carbohydrate in an unknown sample a. Molisch Test b. Benedict's Test c. Barfoed's Test d. Osazone Test e. Seliwanoff's Test 2) What are the reagents used and what are the components of each of these reagents enumerated in number 1 a. Molisch Reagent and Sulfuric Acid o Components: Molisch Reagent-A solution of ∝-naphthol in ethanol. b. Benedict's Reagent o Components: A mixture of Sodium carbonate, Sodium citrate and Copper (II) sulfate pentahydrate. c. Barfoed's Reagent o Components: 0.33 molar solution of neutral Copper acetate in 1% Acetic acid solution. d. Phenylhydrazine Mixture o Components: 0.5 g of Phenylhydrazine hydrochloride, 0.1 gram of Sodium acetate and 10 drops of Glacial Acetic acid. e. Seliwanoff Reagent o Components: Resorcinol and Concentrated Hydrochloric acid 3) Discuss the principle underlying each of the qualitative test enumerated in No. 1. What will positive results show? a. Molisch's Test o Carbohydrates undergo dehydration when heated with concentrated H2SO4 to form furfural derivatives. Furfural derivatives obtained are condensed with alpha-naphthol to give colored compounds hence the presence of carbohydrate is confirmed. The positive result yielded will be a purple ring. b. Benedict's Test o Reduction-reaction is carried out in a weak alkaline medium through the presence of sodium carbonate. CuSO4.7H2O in an alkaline citrate solution is the reagent that would participate in the reduction process. The copper in the Benedict's reagent is reduced to Copper (II) Oxide, which then precipitates. The reducing sugar would be the reducing agent, giving out electrons in the copper-containing reagent and allowing precipitation to occur. c. Barfoed's Test o The reaction is based on the reduction of cupric acetate by reducing monosaccharides and reducing disaccharides. The reaction with disaccharides is slower because disaccharides have to get hydrolyzed first and then react with the reagent cupric acetate to produce cuprous oxide. The positive result will be a brick-red precipitate. d. Osazone Test o Osazone formation is an indication of the presence of reducing sugars. The reaction between phenylhydrazine and the carbonyl group of the sugar form phenylhydrazone,

Volume 7, Issue 2, 2008

There is a multitude of chemical and biochemical detection methods for sugars. Which ones would be most practical in an undergraduate laboratory setting? How to best detect non-reducing disaccharides? How to make such lab fun for students to perform? After trying several spectrophotometric methods, it was found that chemical detection by dinitrosalicylic acid and biochemical detection by hexokinase/glucose-6-phosphate dehydrogenase reagent are most appropriate. Sucrose, a non-reducing disaccharide was digested chemically with hydrochloric acid and biochemically with invertase. It was concluded that chemical detection and biochemical detection compliment each other. Chemical digestion method was preferred over the digestion by invertase. These methods were applied for testing the validity of sugar ingredients printed on drink labels as well as the measurement of sugar levels in ripening bananas at two different conditions. The comprehensive comparison of these methods and the detecti...

La France byzantine, 2015

Les monuments de style classique dans les villes égyptiennes de la chôra, 2022

Mimesis eBooks, 2017

Journal of Advanced Physics, 2015

Psychology Research, 2023

Contra el realisme capitalista, comunisme àcid. Antologia de K-Punk, Manifest, 2024

Aplikacija industrije 4.0 – prilika za novi iskorak u svim industrijskim granama / Application of Industry 4.0 – an opportunity for a new step forward in all industrial branches, 2022

www.sismel.it

Ultrasonics Sonochemistry, 1999

Psychological Reports, 1998

Andamios, 2004

Health and Quality of Life Outcomes

Journal of Applied Polymer Science, 2021

Holos Environment, 2014

•   We're Hiring!
•   Help Center
• Find new research papers in:
• Health Sciences
• Earth Sciences
• Cognitive Science
• Mathematics
• Computer Science
• Academia ©2024

• Chemistry Practicals
• CBSE Class 12 Chemistry Practical
• Tests Of Carbohydrates

Tests of Carbohydrates

Carbohydrates are the most abundant and diverse class of organic compounds occurring in nature. It played a key role in the establishment and evolution of life on earth by creating a direct link between the sun and chemical energy.

Table of Contents

• Materials Required
• Apparatus Setup
• Observations and Inference
• Results and Discussions
• Precautions

Frequently Asked Questions on Tests of Carbohydrates

To study some simple tests of carbohydrates in the given sample.

The word carbohydrate is formed from the words carbon and hydrogen. Carbohydrates are combinations of the chemical elements carbon and hydrogen plus oxygen. In the natural world, carbohydrates are the most common chemical compound used for food.

The following are the tests to identify the presence of carbohydrates.

• Molisch’s test
• Fehling’s test
• Benedict’s test
• Tollen’s test
• Iodine test

(a) Molisch’s Test:

Molisch’s test is a general test for carbohydrates. This test is given by almost all of the carbohydrates. In this test, concentrated sulfuric acid converts the given carbohydrate into furfural or its derivatives, which react with α-naphthol to form a purple coloured product.

The chemical reaction is given below.

(b) Fehling’s Test:

This test is given by reducing sugars. To the aqueous solution of carbohydrate fehling’s solution is added and heated in water bath. The formation of red precipitate confirms the presence of reducing sugars. The copper ions present in fehling’s solution in +3 state is reduced to +2 oxidation state and in alkaline medium it is precipitated as red cuprous oxide .

Note: The appearance of red precipitate confirms the presence of carbohydrates.

(c) Benedict’s Test:

This test is given by reducing sugars. in an alkaline medium, sodium carbonate converts glucose to enediol and this enediol reduces cupric to cuprous forming cuprous hydroxide. This solution is kept in sodium citrate and on boiling, red precipitate of cuprous oxide is formed.

(d) Tollen’s Test:

This test is given by reducing sugars. Carbohydrates react with Tollens reagent and forms a silver mirror on the inner walls of the test tube. This confirms the presence of reducing sugars. Silver ions are reduced to metallic silver.

(e) Iodine Test:

This test is only given by starch. Starch reacts with iodine solution forms complex blue colour solution. On heating the blue colour disappears and on cooling the blue colour reappears.

Materials Required:

• Molisch’s reagent
• Fehling’s reagent
• Benedict’s reagent
• Tollen’s reagent
• Iodine solution
• Concentrated sulfuric acid
• Sodium hydroxide solution
• Test tube holder
• Test tube stand
• Bunsen burner

Apparatus Setup:

Preparation of Reagents:

• Molisch’s reagent – It is prepared by adding α-naphthol in 10% alcoholic solution.
• Fehling’s reagent – It is a solution of 1ml each of Fehling’s A and Fehling’s B
• Fehling’s solution A – Dissolve copper sulfate in distilled water and add a few drops of sulfuric acid.
• Fehling’s solution B – Dissolve sodium potassium tartrate and sodium hydroxide in 150ml of distilled water.
• Benedict’s reagent – To a solution of sodium citrate 0.25g of anhydrous sodium carbonate in distilled water is added and copper sulfate solution is added to it. Make the total volume up to 125ml by adding distilled water.
• Tollen’s reagent – Add sodium hydroxide solution to the silver nitrate solution. Then add ammonium hydroxide solution dropwise till the precipitate dissolves. The clear solution is called Tollens reagent.
• Iodine solution – Iodine solution is obtained by dissolving iodine in potassium iodide solution.
• Take 2ml of the given sample solution in a clean test tube.
• Add 2-3 drops of Molisch reagent slowly.
• Now add concentrated sulfuric acid along the sides of the test tube.
• The acid layer forms a layer at the bottom.
• Note the junction of the two layers.
• If there is a formation of the violet ring then the presence of carbohydrate is confirmed.
• Take 2ml of given sample solution in a clean test tube.
• Add 2 ml of Fehling’s solution A and Fehling’s solution B to it.
• Keep the solution in a boiling water bath for about 10 minutes.
• If there is the formation of red precipitate then the presence of carbohydrate is confirmed.
• Take the given sample solution to be tested in a clean test tube.
• Add 5ml of Benedict’s reagent to it.
• Boil the solution for about 2 minutes.
• Cool the solution and observe the solution.
• If there is formation of green, red or yellow precipitate then there is presence of reducing sugars.
• Take the given sample solution in a clean test tube.
• Add 2-3ml of tollens reagent to it.
• Keep the test tube in a boiling water bath for 10 minutes.
• If there is the appearance of shiny silver mirror confirms the presence of reducing sugars.
• Take the sample solution to be tested in a clean test tube.
• Add 2-3 drops of iodine solution.
• Observe the change in colour.
• If there is the appearance of a blue colour then the presence of starch is confirmed.

Observations and Inference:

Results and discussions:.

The given organic compound is a _________ (reducing sugar/starch/carbohydrate) compound.

Precautions:

• Handle the acids like concentrated sulfuric acid with care.
• Always use droppers to take reagents from the reagent bottles.
• While heating the reaction mixture do it carefully.

Also, Check ⇒ Structure & Properties of Maltose

What are carbohydrates?

Carbohydrates are polyhydroxy aldehydes, ketones or compounds that are transformed into one of a large group of organic compounds that occur in foods and living tissues, including sugars, starch and cellulose.

What is Fehling’s solution?

Fehling’s solution is prepared by mixing two solutions Fehling’s A and Fehling’s B. Fehling’s A contains copper sulfate solution whereas Fehling’s B contains potassium hydroxide and potassium sodium tartrate.

If a compound gives a positive test for iodine test, what is the nature of the compound?

If a chemical compound gives positive iodine test then the given organic compound is starch.

What are the most important constituents of food?

Carbohydrates, proteins and fats are the most important constituents of food.

What are reducing and non-reducing sugars?

Non-reducing sugars do not have an OH group attached to the anomeric carbon so other compounds cannot be reduced. Glucose is a reducing sugar. A disaccharide may be a reducing sugar or non-reducing sugar. Maltose is a reducing sugar, while sucrose is a non-reducing sugar.

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

Visit BYJU’S for all Chemistry related queries and study materials

Your result is as below

Request OTP on Voice Call

Leave a Comment Cancel reply

Your Mobile number and Email id will not be published. Required fields are marked *

Post My Comment

Register with BYJU'S & Download Free PDFs

Register with byju's & watch live videos.