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Question #44997

Difficulty: 8/10 | 🟢 Free

The Question

An aqueous solution containing $1\text{ mol}$ of sucrose and $1\text{ mol}$ of lactose is subjected to complete acidic hydrolysis. The resulting mixture is then treated with an excess of phenylhydrazine in an acetate buffer (pH $\approx 4.5$ ) at $373\text{ K}$ until the reaction is complete. Let $P$ be the total moles of phenylhydrazine consumed, $Q$ be the total moles of osazones formed, and $R$ be the number of structurally distinct osazones obtained. Identify the correct set of values for $P$ , $Q$ , and $R$ .

Options

A.
$P = 12$ , $Q = 4$ , $R = 2$
B.
$P = 12$ , $Q = 4$ , $R = 1$
C.
$P = 8$ , $Q = 4$ , $R = 2$
D.
$P = 12$ , $Q = 4$ , $R = 3$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Disaccharide Hydrolysis Products|Osazone Formation Logic|D-Glucose Anomeric Equilibrium

Why This Question Is Tricky

Common Mistakes

The question tests the stoichiometry of osazone formation and the stereochemical constraints of the reaction.

The primary trap is the rote-memorization that 'all common hexoses form the same osazone.' While D-glucose, D-mannose, and D-fructose form the same osazone due to identical stereochemistry at C3, C4, and C5, D-galactose is a C4 epimer and forms a diastereomeric osazone.

Additionally, students often mistake the stoichiometry of phenylhydrazine, assuming 2 moles are consumed instead of 3 (failing to account for the mole used to oxidize the alpha-hydroxyl group).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Biomolecules - Class 12
Concept	Disaccharide Hydrolysis Products
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free