Question

4. Indicate what will happen (color change) in the following conditions:

A. Mix McDonald’s Sweet Tea with Benedict’s Solution:__________________.

B. Mix pureed yams with iodine:_____________________________________.

C. Mix a salad dressing of herbs/oil with Sudan Solution:__________________.

D. Mix pureed tofu with Biuret’s Solution:______________________________.

Answer 1

Q4) a) When Mc.Donalds sweet tea is mixed with Benedict’s solution

Answer- Clear blue solution changes to Brick red precipitate.

Explanation- Mc.donalds sweet tea contains reducing sugar, Benedict’s reagent is used to detect presence of reducing sugar. These reducing sugars have an aldehyde functional group, which can reduce soluble copper (II) ions in copper (II) sulphate to insoluble copper (I) ions. Blue copper (II) ions from copper (II) sulphate are reduced to red copper (I) ions, by the aldehyde groups in the reducing sugar.

Q4) b) Mix pureed yam with Iodine

Answer- Iodine color changes from brown to purple.

Explanation- Yam contains starch in it, the presence of starch causes iodine to change its color. Starch is a carbohydrate and it exists in two types of molecules amylose and amylopectin, reaction between amylose or amylopectin and iodine causes the color change.

Q4) c) Mix a salad dressing of herbs/ oils with sudan solution.

Answer- oils are stained red with sudan solution.

Explanation- sudan III is lysochrome diazo dye used to color non polar substances like oils, lipids, triglycerides.

Q4) d) Mix pureed tofu with Biurete’s solution.

Answer- Blue color of Biuret’s reagent changes to violet color indicating the presence of protein.

Explanation- Tofu puree contains high amount of protein so it gives a violet color, as it contains large number of peptide bonds in it.

Biuret reagent contains sodium hydroxide and copper(II) sulphate and is used for determining the presence of protein in a sample. In this test there is a reaction between copper ions and peptide bonds in an alkaline solution, this gives rise to the violet color which indicates the presence of protein.