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Question #44668

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The Question

A neutral mixed-valence transition metal cluster has the empirical formula \ce{M2L5} (where \ce{L} is a monoanionic ligand), implying an average fractional oxidation state of $+2.5$ for the metal \ce{M}. To resolve this fractional state, the cluster exists in benzene as a discrete, undissociated hexanuclear species containing \ce{M^{2+}} and \ce{M^{3+}} ions in a $1:1$ ratio.

A solution is prepared containing exactly $1.0\text{ mole}$ of the empirical formula unit \ce{M2L5} per $1.950\text{ kg}$ of benzene (\ce{C6H6}, molar mass = $78\text{ g mol}^{-1}$ ).

Given that the vapor pressure of pure benzene at $298\text{ K}$ is $152.0\text{ Torr}$ , calculate the vapor pressure of the solution at $298\text{ K}$ . (Assume ideal behavior).

Options

A.
$150.0\text{ Torr}$
B.
$146.2\text{ Torr}$
C.
$151.0\text{ Torr}$
D.
$118.8\text{ Torr}$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Concentration Unit Interconversion|Vapor Pressure Lowering (Mole Fraction)|Fractional Oxidation State Misconception

Why This Question Is Tricky

Common Mistakes

The question tests the distinction between empirical and molecular formulas in colligative properties.

The 'Chemical Exception' is the fractional oxidation state misconception: mixed-valence compounds form larger discrete clusters to satisfy integer oxidation states.

The trap is using the empirical formula directly for concentration calculations.

Students must recognize that 'hexanuclear' means 6 metal centers, requiring a conversion from the given moles of the empirical unit (2 metals) to the actual moles of the cluster (6 metals).

Failing to do so yields the incorrect vapor pressure of 146.2 Torr.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Some Basic Concepts of Chemistry - Class 11 Part 1
Concept	Concentration Unit Interconversion
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free