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

i) State two advantages of the H

_{2}

–O

_{2}

fuel cell over an ordinary cell.
ii) Silver is electrodeposited on a metallic vessel of total surface area 900 cm

^{2}

by passing a current of 0.5 A for two hours. Calculate the thickness of silver deposited.
(Given: density of silver = 10.5 g cm

^{- 3}

, atomic mass of silver = 108 u, F = 96500 C mol

^{- 1}

)

Solution

(i) Advantages of the H

_{2}

–O

_{2}

fuel cell: (1) much higher thermodynamic efficiency (~70%) than combustion-based generation (~40%); (2) pollution-free — the only product is water; (3) it runs continuously as long as fuel is supplied and never goes dead. (Any two.)
(ii) Charge:

Q = I t = 0.5 \times 7200 = 3600 C

Moles of Ag:

n = \frac{3600}{96500} = 0.0373 mol; m = 0.0373 \times 108 = 4.03 g

Volume:

V = \frac{4.03}{10.5} = 0.384 c m^{3}

Thickness:

t = \frac{0.384}{900}

t = 4.26 \times 1 0^{- 4} cm

CBSE Class 12 Board · 2006 · All India · Subjective

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

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