Question

Carbohydrates can be tested by using-

• A. Iodine solution
• B. Caustic soda
• C. Copper sulphate
• D. None of these

Answer 1

The correct option is A

Iodine solution

The explanation for the correct option.

(A) - Iodine solution

Carbohydrates can be detected by using an iodine solution.

• If we mix iodine with a substance that contains carbohydrates in it the substance will turn blue or black and if no carbohydrate is present then it will remain in the same colour that it was initially.
• But if we talk about simple sugar that contains aldehyde in the structure we can do a Fehling test also to detect the presence of reducing sugar like glucose.

(Copper sulphate and caustic soda)Fehling test:

• Fehling solution is a mixture of the blue-coloured aqueous solution of copper sulphate(${\mathrm{CuSO}}_4$) and a colourless aqueous solution of potassium sodium tartrate (${\mathrm{KNaC}}_4{\mathrm{H}}_4{\mathrm{O}}_6·4{\mathrm{H}}_2\mathrm{O}$, also known as Rochelle salt) in an alkaline base like sodium hydroxide (NaOH).
• If we add Fehling solution with reducing monosaccharides like glucose the red colour precipitate will form which confirms the presence of monosaccharides.

Reducing sugar: A sugar that has the capability to reduce the reagent is called a reducing agent.

For example, Glucose, galactose, etc.

The explanation for incorrect options.

(B) and (C)

• Copper sulphate and caustic soda together are used for the identification of the protein.
• It is known as a biuret test.
• During this test will get a violet colour which indicates the presence of proteins.

Hence option (A) is the correct answer.