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Question #44994

Difficulty: 8/10 | 🟢 Free

The Question

An aqueous solution containing $17.1 \text{ g}$ of sucrose ( $\ce{C12H22O11}$ , molar mass $= 342 \text{ g/mol}$ ) is completely hydrolyzed using dilute $\ce{H2SO4}$ at $298 \text{ K}$ . The resulting mixture is neutralized and treated with an excess of Tollens' reagent ( $\ce{[Ag(NH3)2]+}$ in aqueous $\ce{NaOH}$ ). Assuming complete oxidation of all reactive monosaccharides, what is the total mass of metallic silver deposited? (Atomic mass of $\ce{Ag} = 108 \text{ g/mol}$ )

Options

A.
21.6 \text{ g}
B.
10.8 \text{ g}
C.
43.2 \text{ g}
D.
5.4 \text{ g}

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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|Tollens vs. Fehling Specificity|Reducing Sugar Criteria

Why This Question Is Tricky

Common Mistakes

This question tests the student's mechanistic understanding of reducing sugars beyond rote memorization.

A common misconception is that Tollens' reagent strictly oxidizes aldehydes, leading students to conclude that ketoses like D-fructose will not react.

The hidden variable is the alkaline nature of Tollens' reagent, which catalyzes the Lobry de Bruyn-van Ekenstein transformation.

This tautomerization converts the $\alpha$ -hydroxy ketone (fructose) into an equilibrium mixture of aldoses (glucose and mannose) via an enediol intermediate.

Students who fall for the trap will only calculate the silver deposited from the D-glucose fraction, yielding exactly half the correct mass ( $10.8 \text{ g}$ ).

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