QJEEM18Chf0a0: JEE Main 2018 Chemistry - Class 12 JEEM18Chf0a0 Solution: How long (approximate) should water be electrolysed by passing…

Required reaction :

B₂H₆ + 3O₂ $\to$ B₂ O₃ + 3 H₂ O

Here molar mass of B₂H₆ =10.8 $\times$ 2 + 6 = 27.6 gm

Given weight of B₂H₆ = 27.66 g

$\therefore\,\,\,\,$ No of moles of B₂H₆ = ${{27.6} \over {27.66}} \simeq 1$ mole.

For combustion of 1 mole B₂H₆ 3 moles O₂ required.

This 3 mole of O₂ is obtained by electrolysis of H₂O.

2H₂O( $l$ ) $\to$ O₂ (g) + 4 H⁺ (aq) + 4 e ^$-$

From Faradays law of electrolysis,

moles $\times$ n_f = ${{It} \over {96500}}$

Here moles of O₂ = 3.

N_f of O₂ = 4 (in H₂ change of O = $-$ 2

and in O₂ change of 0 = O.

So change in charge = 2 .

for two atoms of O₂ change in charge = 2 $\times$ 2 = 4)

$\therefore\,\,\,\,$ 3 $\times$ 4 = ${{100 \times t} \over {96500}}$

$\Rightarrow \,\,\,\,$ t = 12 $\times$ 965 sec.

$\Rightarrow \,\,\,\,$ t = ${{12 \times 965} \over {60 \times 60}}$ hr

= 3.2 hr