Question

A gas mixture of 40% He and 60% Ne is passed through a diffusion tube, if the amount of He is recovered is 20% of the input, what is the percentage of He in the product?

(a) 25 %

(b) 33.3 %

(c) 50 %

(d) 66.6 %

The question was asked in an interview for job.

My question is taken from Solving Material Balance Problems for Single Units in portion A General Strategy for Solving Material Balance Problems and Solving Material Balance Problems for Single Units of Basic Chemical Engineering

Answer 1

Right option is (a) 25 %

Explanation: Let the amount of input be F, He balance: 0.4(F) = 1(0.2F) + x(F – 0.2F), => x = 0.25, => Percentage of He in the product = 25%.