Content Curator
Molisch's test is a chemical method for determining whether or not an analyte contains carbohydrates. Hans Molisch, a Czech-Austrian botanist, is credited with the development of this test. Molisch's test is done by mixing the analyte with Molisch's reagent (an ethanol solution of -naphthol) and then adding some drops of concentrated H2SO4 (sulphuric acid) to the mixture.
The presence of carbohydrates in the analyte is confirmed by the creation of a purple or purplish-red ring at the point of contact between the H2SO4 and the analyte + Molisch's reagent combination. Almost all carbs provide a positive result in Molisch's test. It should be mentioned that this test is positive for several glycoproteins and nucleic acids.
| Table of Content |
Key Takeaways: Molisch Test, carbohydrates, Glycoproteins, Nucleic Acids, Molisch’s Reagent.
Test Principle of Molisch
[Click Here for Sample Questions]
Molisch's test is a carbohydrate test that may be used for any type of carbohydrate. Carbohydrates are dehydrated in this test when they are treated with conc.H2SO4 to create furfural and its variants.
Molisch Test Reaction
The -OH group of sugar is eliminated in the form of water when monosaccharides are processed with conc.H2SO4, and furfural is generated from pentose sugar while hydroxymethyl furfural is created from hexose sugar. Sulphonated-naphthol interacts with these compounds to produce a violet red tinted complex.
Also Read:
| Related Articles | ||
|---|---|---|
| Test for Fats | Test for Protein | Lipids |
| Maltose Structure | Sucrose Structure | Carboxylic Acids |
| Tollen’s Test | Nucleophilic Addition Reaction | Etard Reaction |
Reagents Required
[Click Here for Sample Questions]
- Dry Test Tubes
- Solutions: Glucose 5%, Sucrose 5%, Starch 5%
- H2SO4
- Pipettes
- 5% α naphthol in ethanol ( Molisch reagent)
Procedure
[Click Here for Sample Questions]
- Fill a dry test tube with 2 ml of the sample.
- In a separate tube, place 2ml of distilled water as a control.
- To the solution, add 2-3 drops of Molisch's reagent.
- Pipette 1ml concentrated H2SO4 along the tube's wall to create two different levels.
- Look for colour shifts at the intersection of two layers.
- The presence of carbs is indicated by the presence of purple hue.
Observation
[Click Here for Sample Questions]
The existence of carbohydrates is confirmed by the appearance of a purple hue at the contact between both the acid and test layers.
Molisch Test Result
Positive Results: If the test solution produces purple or purplish-red coloured layers, carbohydrates are present. As an outcome, the Molisch test yields good results.
Negative Results: The test solution is free of carbohydrate molecules if it does not give purple or purplish-red coloured layers. As an outcome, the Molisch test yields negative results.
Things to Remember
[Click Here for Sample Questions]
- Molisch test is used to determine whether an analyte contains carbohydrates.
- Molisch test gives a positive result to glycoproteins and nucleic acids.
- Positive results are indicated by a purplish red layer.
- The carbohydrate should have at least five carbons because the process includes the creation of five-carbon furfural derivatives.
- Proteins and lipids with a carbohydrate linked can also cause this test to be positive.
- Not purple colour indicates a false-negative result due to impurities in the reagent.
Also Read:
Sample Questions
Ques. What do you mean by the molisch test? [2 marks]
Ans. The Molisch test is a chemical procedure for detecting carbohydrates in a mixture or solution. Carbohydrates can be attached to lipids or proteins, or they might exist in their natural state. It is also used to determine and discriminate between substances that can be degraded into monosaccharides, such as glycolipids.
Ques. What is the principle of the Molisch test? [2 marks]
Ans. The Molisch test is based on the idea that concentrated acid aids in the dehydration of sugars (carbohydrates) in order to create furfural (from pentose).
Ques. What precautions should you take before completing the Molisch test? [2 marks]
Ans.
1) Because the test requires the use of concentrated acids, more caution must be exercised when handling concentrated acids.
2) The test tube must be held stationary on unmovable test tube holders to guarantee the creation of a purple ring at the junction.
3) To avoid charring the sugars, the strong acid should be poured gently.
4) For reliable findings, 4-5 test tubes must be prepared.
5) To reduce the likelihood of contaminants interacting with the reagent or concentrated acid, distilled water must be used.
6) Green rings can develop as a result of impurities, which might lead to erroneous conclusions.
Ques. Explain how the Molisch Test may be used. [2 marks]
Ans. The following are a few examples of Molisch Test applications.
- The Molisch test is used to determine if a sample is made up of carbohydrates.
- As a by-product of various activities, it can be utilised to identify carbohydrates from other biomolecules.
Ques. Make a list of the Molisch Test's drawbacks? [2 marks]
Ans. The following are some of the Molisch Test's drawbacks.
- Trioses and tetroses do not produce a favourable outcome in this reaction because they lack the five carbon atoms essential for furfural production.
- The Molisch test does not distinguish between carbohydrates and non-carbohydrates. Furfurals or furfural-like compounds can be made from citric acids, lactic acids, oxalic acids, formic acids, and other organic acids.
Ques. What is the positive result of the Molisch Test? [2 marks]
Ans. If the test solution produces purple or purplish-red coloured layers, carbohydrates are present. As an outcome, the Molisch test yields good and positive results.
Ques. What is the negative result of the Molisch test? [2 marks]
Ans. The test solution is free of carbohydrate molecules if it does not give purple or purplish-red coloured layers. As an outcome, the Molisch test yields negative and bad results.
Ques. The Molisch test detects which types of carbohydrates? [2 marks]
Ans. Molisch test results are positive for all carbohydrates (monosaccharides, disaccharides, and polysaccharides). It works by dehydrating the carbohydrate with Sulphuric acid to make an aldehyde, which then distils with two molecules of -naphthol to form a purple ring at the interface.
Ques. What is the significance of the Molisch test as a general carbohydrate test? [2 marks]
Ans. Monosaccharides provide a positive result faster in Molisch's test. Disaccharides and polysaccharides, on the other hand, react slowly with Molisch reagent and produce a delayed positive result. As a result, Molisch's carbohydrate test is quite helpful in detecting the presence of carbs in a product.
For Latest Updates on Upcoming Board Exams, Click Here: https://t.me/class_10_12_board_updates
Check-Out:
Comments