JEE Main · 2018 · 08 Apr 2018 · Offline · Redox Reactions and Electrochemistry

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How long (approximate) should water be electrolysed by passing through 100 amperes current so that the oxygen released can completely burn 27.66 g of diborane ?
(Atomic weight of

B = 10.8 u

)

(A)1.6 hours
(B)6.4 hours
(C)0.8 hours
(D)3.2 hours✓ Correct

Answer: (D)

Solution

The molar mass of diborane is

B X_{2} H X_{6} = 2 (10.8) + 6 = 27.6

g/mol, so

27.66

g is exactly one mole. Its combustion,

B X_{2} H X_{6} + 3 O X_{2} B X_{2} O X_{3} + 3 H X_{2} O

, needs

3

mol of

O X_{2}

, and electrolysing water,

2 H X_{2} O 2 H X_{2} + O X_{2}

, releases one mole of

O X_{2}

for every

4

faradays, so

3

mol demands

12

faradays, that is

12 \times 96500

C. At

100

A the time is

t = \frac{12 \times 96500}{100} = 11580

s, about

3.2

hours.

JEE Main · 2018 · 08 Apr 2018 · Offline · Single correct option

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