Question

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

(Atomic weight of B = 10.8 u)

Options

• 6.4 hours

• 0.8 hours

• 3.2 hours

• 1.6 hours

Answer 1

3.2 hours

Explanation:

Reaction of diborane with oxygen:

\[\ce{B2H6 + 3O2 −> B2O3 + 3H2O}\]

1 mole of B₂H₆ requires 3 moles of O₂.

Molar mass of B₂H₆ = 2 × 10.8 + 6 × 1 = 27.62 g

Therefore, 27.6 g of B₂H₆ corresponds to 1 mole, which requires 3 moles of O₂ for complete combustion.

Electrolysis of water produces O₂.

\[\ce{2H2O -> 2H2 + O2}\]

1 mole of O₂ = 4 Faradays (4 × 96500 C)

3 moles O₂ = 3 × 4F = 12F

Q = 12 × 96500

= 1,158,000 C

Time (t) = `Q/I`

= `1158000/100`

= 11580 seconds

To convert seconds into hours:

Time in hours = `11580/(3600  "s/hour")`

= 3.22 hours