Virtual Labs

Quantitative estimation of sugars

1. What happens to non-reducing sugars during hydrolysis in the presence of dilute acid?

a: They are oxidized to form acids. Explanation

Explanation

b: They are reduced to form aldehydes. Explanation

Explanation

c: They are converted into reducing sugars. Explanation

Explanation

d: They are precipitated out of the solution. Explanation

Explanation

2. Why is the DNS method preferred over Benedict’s test for quantitative estimation?

a: It detects non-reducing sugars directly. Explanation

Explanation

b: It forms a colored complex measurable with a spectrophotometer. Explanation

Explanation

c: It does not require heating. Explanation

Explanation

d: It is more specific to sucrose. Explanation

Explanation

3. In Benedict’s test, what does the intensity of the color change (blue to brick-red) indicate?

a: The acidity of the solution. Explanation

Explanation

b: The concentration of reducing sugars. Explanation

Explanation

c: The presence of proteins. Explanation

Explanation

d: The amount of non-reducing sugars. Explanation

Explanation

4. What is the key observation in Fehling’s test for reducing sugars?

a: Formation of a green ring. Explanation

Explanation

b: Appearance of a violet color. Explanation

Explanation

c: Formation of a brick-red precipitate. Explanation

Explanation

d: Emission of gas bubbles. Explanation

Explanation

5. What is the purpose of preparing a standard curve in the DNS method?

a: To identify the type of sugar present. Explanation

Explanation

b: To calculate the pH of the solution. Explanation

Explanation

c: To determine the exact concentration of reducing sugars in the sample. Explanation

Explanation

d: To differentiate reducing sugars from non-reducing sugars. Explanation

Explanation

6. What step is essential before testing non-reducing sugars like sucrose using Benedict’s test?

a: Adding DNS reagent. Explanation

Explanation

b: Neutralizing the solution with NaOH. Explanation

Explanation

c: Hydrolyzing with dilute acid. Explanation

Explanation

d: Boiling with Fehling’s solution. Explanation

Explanation

7. Which of the following is a hydrolysis product of sucrose?

a: Glucose and galactose Explanation

Explanation

b: Glucose and fructose Explanation

Explanation

c: Glucose and mannose Explanation

Explanation

d: Fructose and galactose Explanation

Explanation

8. Why are Fehling’s and Benedict’s tests not suitable for estimating polysaccharides like starch?

a: Polysaccharides are too large to react with the reagent. Explanation

Explanation

b: Polysaccharides do not have free aldehyde or ketone groups. Explanation

Explanation

c: The reagents get neutralized by polysaccharides. Explanation

Explanation

d: The reaction forms a colorless product. Explanation

Explanation

9. Which sugar is likely present if hydrolyzed sample tests positive, but the unhydrolyzed sample does not?

a: Glucose Explanation

Explanation

b: Fructose Explanation

Explanation

c: Sucrose Explanation

Explanation

d: Maltose Explanation

Explanation

10. What conclusion can be drawn if a sample does not give a positive result with Benedict’s or DNS reagent?

a: It contains only non-reducing sugars. Explanation

Explanation

b: It contains reducing sugars. Explanation

Explanation

c: It contains proteins instead of sugars. Explanation

Explanation

d: The sample is highly acidic. Explanation

Explanation