Redox Reactions and Electrochemistry — CBSE Class 12 · 2006 · All India Board Question with Solution

a) Give reasons for the following:
i) Rusting of iron is quicker in saline water than in ordinary water.
ii) Aluminium metal cannot be produced by the electrolysis of an aqueous solution of an aluminium salt.
b) The resistance of a conductivity cell filled with 0.1 M KCl solution is 100 ohm. If the resistance of the same cell when filled with 0.02 M KCl solution is 520 ohm, calculate the conductivity and molar conductivity of the 0.02 M KCl solution. The conductivity of 0.1 M KCl solution is 1.29 S m

^{- 1}

Solution

(a)(i) In saline water the dissolved NaCl increases the conductivity of the water film on the iron; the electrochemical corrosion cell works faster, so rusting is quicker.
(ii) The reduction potential of water is higher than that of Al

^{3 +}

, so at the cathode water is reduced to H

_{2}

instead of Al

^{3 +}

being deposited.
(b) Cell constant (κ = 1.29 S m

^{- 1}

= 0.0129 S cm

^{- 1}

G^{*} = κ \times R = 0.0129 \times 100 = 1.29 c m^{- 1}

For the 0.02 M solution:

κ = \frac{1.29}{520} = 2.48 \times 1 0^{- 3} S c m^{- 1} = 0.248 S m^{- 1}

Λ_{m} = \frac{κ \times 1000}{C} = \frac{2.48 \times 1 0 ^{- 3} \times 1000}{0.02}

Λ_{m} = 124 S c m^{2} mo l^{- 1}

CBSE Class 12 Board · 2006 · All India · Subjective

CBSE Class 12 · 2006 · All India · Redox Reactions and ElectrochemistryLong Answer

Solution

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