CBSE Class 12 · 2009 · Redox Reactions and ElectrochemistryLong Answer

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a) Write the anode and cathode reactions and the overall reaction occurring in a lead storage battery.
b) A copper–silver cell is set up. The copper ion concentration is 0.10 M. The concentration of silver ion is not known. The cell potential measured is 0.422 V. Determine the concentration of silver ions in the cell.
(Given:

E_{A g^{+} /Ag}^{\circ} = + 0.80

E_{C u^{2 +} /Cu}^{\circ} = + 0.34

Solution

(a) Lead storage battery (discharge):
Anode:

Pb + S O_{4}^{2 -} ⟶ PbS O_{4} + 2 e^{-}

Cathode:

Pb O_{2} + S O_{4}^{2 -} + 4 H^{+} + 2 e^{-} ⟶ PbS O_{4} + 2 H_{2} O

Overall:

Pb + Pb O_{2} + 2 H_{2} S O_{4} ⟶ 2PbS O_{4} + 2 H_{2} O

(b)

E_{ce l l}^{\circ} = 0.80 - 0.34 = 0.46

n = 2

0.422 = 0.46 - 0.0295 lo g \frac{0.10}{x ^{2}}

lo g \frac{0.10}{x ^{2}} = 1.288 \Rightarrow x^{2} = \frac{0.10}{19.4} = 5.15 \times 1 0^{- 3}

[A g^{+}] = 0.072 M

CBSE Class 12 Board · 2009 · Subjective

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CBSE Class 12 · 2009 · Redox Reactions and ElectrochemistryLong Answer

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