Question

Molten $AlC{l}_3$ is electrolysed with a current of 0.5 ampere to produce 27 g Al. The volume of O${}_2$ is formed per hour at STP in litre is:

• A. 3
• B. 1.5
• C. 0.05
• D. 0.1

Answer 1

Answer: (D)

0.1

27 g of Al corresponds to 1 mol of Al. They require 3 faraday of electricity.
The time required for deposition of 27 g Al is $\frac{3\times 96500}{0.5}=579000s=160.8hr$
1 mole of oxygen corresponds to faraday of electricity.
Hence, 3 faraday of electricity will correspond to 0.75 moles of oxygen which will occupy a volume of $0.75\times 22.4=16.8$L at STP.
This volume is liberated in 160.8 hours.
Hence, the volume of oxygen liberated per hour will b $\frac{16.8}{160.8}=0.1$L.