Question

A gaseous mixture composed of 20% CH4, 30% C2H4, 35% C2H2, and 15% C2H2O. What is the average molecular weight of the mixture?

(a) 20

(b) 25

(c) 6.75

(d) 9.25

This question was addressed to me in class test.

The doubt is from Analyses of Multicomponent Solutions and Mixtures topic in chapter Moles, Density & Concentration of Basic Chemical Engineering

Answer 1

Right option is (c) 6.75

To elaborate: Since it is a gaseous mixture so the percentages are by mole, => average molecular weight of mixture = {(20/100)*16 + (30/100)*28 + (35/100)*26 + (15/100)*42}/4 = 6.75.