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Question
Resistance of conductivity cell filled with 0.1 M KCl solution is 100 ohms. If the resistance of the same cell when filled with 0.02 M KCl solution is 520 ohms, calculate the conductivity and molar conductivity of 0.02 M KCl solution. [Given: Conductivity of 0.1 M KCl solution is 1.29 S m-1 .]
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Solution
Given: For 0.1 M KCl, k = 1.29 S m-1 = 0.0129 S cm-1, R = 100 ohms or 0.02 M KCl, R = 520 ohms
To find: Conductivity and molar conductivity of 0.02 M KCl solution.
Formulae: a. Cell constant, b = k x R
b. Conductivity, k(KCl, 0.02 M) = Cellconstant /Resistance
c.Molar conductivity = 1000 k/C
Calculation: From formula (a),
b = k x R
= 0.0129 x 100 = 1.29 cm-1
From formula (b),
Conductivity, k(KCl, 0.02 M) = Cellconstant/Resistance
= 1.29/520
= 2.48 x 10-3 ohm-1 cm-1
From formula (c),
Molar conductivity of 0.02 M KCl solution = 1000k/C
=(1000 x 2.48 x 10 -3)/0.02
=124 ohm-1 cm2 mol-1
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