Question

A mixture contains 23 g of ethanol and 36 g of water, some acetic acid is added to the mixture and its mole fraction becomes 0.5, how much acetic acid was added?

(a) 25 g

(b) 75 g

(c) 100 g

(d) 150 g

The question was asked during an online exam.

This intriguing question originated from Mole Fraction and Mass(Weight) Fraction topic in division Moles, Density & Concentration of Basic Chemical Engineering

Answer 1

Right answer is (d) 150 g

To explain I would say: Let m grams of acetic acid was added, => 0.5 = (m/60)/{(23/46) + (36/18) + (m/60)}, => m = 150 g.