Class 12 Chemistry
Chapter 3 – Electrochemistry
Magical Series Assignment 6
Q.1. The conductivity of 0.20 M solution of KCl at 298 K is 0.025 S cm–l. Calculate its molar conductivity.
[Ans: 125 S cm2 mol–1]
Q.2. The conductivity of 0.001 M acetic acid is 4 × 10–5 S/cm. Calculate the dissociation constant of acetic acid, if molar conductivity at infinite dilution for acetic acid is 390 S cm2 / mol.
[Ans: 1.18 × 10–5]
Q.3. Molar conductivity of a 1.5 M solution of an electrolyte is found to be 138.9 S cm2 mol–1. Calculate the conductivity of this solution.
[Ans: 0.208 S cm–1]
Q.4. Resistance of a conductivity cell containing 0.001 M KCl solution at 298 K is 1500 Ω. What is the cell constant if conductivity of 0.001 M KCl solution at 298 K is 0.146 × 10–3 S cm–l?
[Ans: 0.219 cm–1]
Q.5. The conductivity of 0.001 mol L–1 solution of CH3COOH is 3.905 × 10–5 S cm–1. Calculate its molar conductivity and degree of dissociation (α).
Given : λo(H+) = 349.6 S cm2 mol–1 and λo(CH3COO–) = 40.9 S cm2 mol–1.
[Ans: 39.05 S cm2 mol–1, 0.1]
Q.6. The conductivity of 0.20 mol L–l solution of KCl is 2.48 × 10–2 S cm–1. Calculate its molar conductivity and degree of dissociation (α).
Given: λo(K+) = 73.5 S cm2 mol–1 and λo(Cl–) = 76.5 S cm2 mol–1.
[Ans: 124 S cm2 mol–1, 0.82]
Q.7. Resistance of a conductivity cell filled with 0.1 mol L–1 KCl solution is 100 Ω. If the resistance of the same cell when filled with 0.02 mol L–1 KCl solution is 520 Ω, calculate the conductivity and molar conductivity of 0.02 mol L–1 KCl solution. The conductivity of 0.1 mol L–1 KCl solution is 1.29 × 10–2 Ω–1 cm–1. [Ans: 0.248 S m–1, 0.0124 S m2 mol–1]
Q.8. The value of Lom of Al2(SO4)3 is 858 S cm2 mol–1, while λo(SO42–) is 160 S cm2 mol–1. Calculate the limiting ionic conductivity of Al3+. [Ans: 189 S cm2 mol–1]
Q.9. The electrical resistance of a column of 0.05 M NaOH solution of diameter 1 cm and length 50 cm is 5.55 × 103 ohm. Calculate its resistivity, conductivity and molar conductivity.
[Ans: 86.35 Ω cm, 1.158 × 10–2 Ω–1 cm–1, 231.6 S cm2 mol–1]
Q.10. When a certain conductance cell was filled with 0.1 M KCl, it has a
resistance of 85 ohms at 25°C. When the same cell was filled with an aqueous
solution of 0.052 M unknown electrolyte, the resistance was 96 ohms. Calculate
the molar conductance of the electrolyte at this concentration.
[Specific conductance of 0.1 M KCl = 1.29 × 10–2 ohm–1 cm–1]
[Ans: 219.61 S cm2 mol–1]
Q.11. Calculate the degree of dissociation of acetic acid at 298 K, given that:
Lm(CH3COOH) = 11.7 S cm2 mol–1.
Lom(CH3COO–) = 49.9 S cm2 mol–1.
Lom(H+) = 349.1 S cm2 mol–1. [Ans: 3 × 10–2]
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