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Solve the following.
Resistance of a conductivity cell filled with solution is . If the resistance of the same cell when…
(i)[3.0]
Resistance of a conductivity cell filled with $0\cdot1\text{ mol L}^{-1}\text{ KCl}$ solution is $100\ \Omega$. If the resistance of the same cell when filled with $0\cdot02\text{ mol L}^{-1}\text{ KCl}$ solution is $520\ \Omega$, calculate the conductivity and molar conductivity of $0\cdot02\text{ mol L}^{-1}\text{ KCl}$ solution. The conductivity of $0\cdot1\text{ mol L}^{-1}\text{ KCl}$ solution is $1\cdot29 \times 10^{-2}\ \Omega^{-1}\text{cm}^{-1}$.
(ii)[2.0]
Define the following terms:
(1) Limiting molar conductivity.
(2) Fuel cell.
Answer
Answer (i)
AICell constant $G^* = \kappa \times R = 1\cdot29 \times 10^{-2}\ \Omega^{-1}\mathrm{cm^{-1}} \times 100\ \Omega = 1\cdot29\ \mathrm{cm^{-1}}$
Conductivity of $0\cdot02\ \mathrm{M}$ KCl: $\kappa = \dfrac{G^*}{R} = \dfrac{1\cdot29\ \mathrm{cm^{-1}}}{520\ \Omega} = 2\cdot48 \times 10^{-3}\ \mathrm{S\ cm^{-1}}$
Molar conductivity: $\Lambda_m = \dfrac{\kappa \times 1000}{C} = \dfrac{2\cdot48 \times 10^{-3} \times 1000}{0\cdot02} = 124\ \mathrm{S\ cm^2\ mol^{-1}}$
Final answer: 124 S cm^2 mol^-1
Answer (ii)
AI(1) Limiting molar conductivity is the molar conductivity of an electrolyte when its concentration approaches zero (infinite dilution).
(2) A fuel cell is a galvanic cell that converts the chemical energy of a fuel (such as $\mathrm{H_2}$) and an oxidant (such as $\mathrm{O_2}$) directly into electrical energy, with the reactants supplied continuously.
From ISC 2018 Specimen Chemistry Paper 1, question 16(a).
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