JEE Main 2025 Apr 7 Shift 1, Chemistry Q10: Colligative Properties

JEE Main2025Apr 7, Shift 1Chemistry

Given below are two statements :

Statement I : Mohr's salt is composed of only three types of ions-ferrous, ammonium and sulphate.

Statement II : If the molar conductance at infinite dilution of ferrous, ammonium and sulphate ions are $x_{1}$ , $x_{2}$ and $x_{3}$ S cm $^{2}$ mol $^{- 1}$ , respectively then the molar conductance for Mohr's salt solution at infinite dilution would be given by $x_{1} + x_{2} + 2 x_{3}$

In the light of the given statements, choose the correct answer from the options given below :

A
Both statements I and Statement II are false
B
Statement I is false but Statement II is true
C
Statement I is true but Statement II are false
D
Both statements I and Statement II are true

Solution

Mohr's salt has the formula FeSO $_{4} \cdot$ (NH $_{4}$ ) $_{2}$ SO $_{4} \cdot$ 6H $_{2}$ O. On dissolution it releases three kinds of ions: Fe $^{2 +}$ , NH $_{4}^{+}$ , and SO $_{4}^{2 -}$ . Statement I is true.

Applying Kohlrausch's law of independent migration, the molar conductance at infinite dilution equals the sum over all ions per formula unit, each weighted by its stoichiometric count. One formula unit yields:

1 Fe $^{2 +}$
2 NH $_{4}^{+}$
2 SO $_{4}^{2 -}$

$∴ Λ_{m}^{\infty} (Mohr’s salt) = x_{1} + 2 x_{2} + 2 x_{3}$

Statement II writes the coefficient of $x_{2}$ as 1 instead of 2, so it is incorrect.

$∴$ Option (3).

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JEE Main 2025 Apr 7 Shift 1, Chemistry Q10: Colligative Properties

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