JEE Main · 2025 · Shift-ImediumEC-142

Given below are two statements: Statement I: Mohr's salt is composed of only three types of ions — ferrous, ammonium…

Electrochemistry · Class 12 · JEE Main Previous Year Question

Question

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 conductan\ce at infinite dilution of ferrous, ammonium and sulphate ions are x1x_1, x2x_2 and x3x_3 S cm2^2 mol−1^{-1}, respectively then the molar conductan\ce for Mohr's salt solution at infinite dilution would be given by x1+x2+2x3x_1 + x_2 + 2x_3.

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

Options
  1. a

    Both statements I and Statement II are false

  2. b

    Statement I is false but Statement II is true

  3. c

    Statement I is true but Statement II is false

    ✓
  4. d

    Both statements I and Statement II are true

Correct Answerc

Statement I is true but Statement II is false

Detailed Solution

Strategy: Identify the components of Mohr's salt and apply Kohlrausch's Law of independent migration of ions. Sum the molar ionic conductivities multiplied by their stoichiometric coefficients.

Step 1: Identify Mohr's Salt Formula: \ce(NH4)2Fe(SO4)2.6H2O\ce{(NH4)_2Fe(SO4)_2.6H2O} Ions produ\ced in solution: \ce(NH4)2Fe(SO4)2→Fe2++2NH4++2SO42−\ce{(NH4)_2Fe(SO4)_2 \rightarrow Fe^{2+} + 2NH_4^+ + 2SO_4^{2-}} Types of ions: Ferrous (\ceFe2+\ce{Fe^{2+}}), Ammonium (\ceNH4+\ce{NH4^+}), and Sulphate (\ceSO42−\ce{SO4^{2-}}). Statement I is Correct. ✓

Step 2: Apply Kohlrausch's Law Λm0=1⋅λ\ceFe2++2⋅λ\ceNH4++2⋅λ\ceSO42−\Lambda_m^0 = 1 \cdot \lambda_{\ce{Fe^{2+}}} + 2 \cdot \lambda_{\ce{NH4^+}} + 2 \cdot \lambda_{\ce{SO4^{2-}}} Using given variables: Λm0=x1+2x2+2x3\Lambda_m^0 = x_1 + 2x_2 + 2x_3 Statement II claims x1+x2+2x3x_1 + x_2 + 2x_3, which is Incorrect (missing the factor of 2 for Ammonium).

Answer: (c) Statement I is true but Statement II is false\boxed{\text{Answer: (c) Statement I is true but Statement II is false}}

Practice this question with progress tracking

Want timed practice with adaptive difficulty? Solve this question (and hundreds more from Electrochemistry) inside The Crucible, our adaptive practice platform.

Practice in The Crucible →Browse Electrochemistry chapter →

More JEE Main Electrochemistry PYQs

2025hard

40 mL of a mixture of CH3COOH and HCl (aqueous solution) is titrated against 0.1 M NaOH solution conductometrically. Which of the following statement is correct?

2025medium

The standard reduction potential values of some of the p-block ions are given below. Predict the one with the strongest oxidising capacity. (a) ESn4+/Sn2+ = +1.15 V (b) ETl3+/Tl = +1.26 V (c)…

2024easy

Identify the factor from the following that does not affect electrolytic conductan of a solution.

2024easy

For a strong electrolyte, a plot of molar conductivity against (concentration)1/2 is a straight line, with a negative slope, the correct unit for the slope is

2024medium

Molar ionic conductivities of divalent cation and anion are 57\ S\ cm2\ mol-1 and 73\ S\ cm2\ mol-1 respectively. The molar conductivity of solution of an electrolyte with the above cation and anion…

View all 65 Electrochemistry PYQs →
Given below are two statements: Statement I: Mohr's salt is composed of only three types of ions —… (JEE Main 2025) | Canvas Classes