Question

What is the mole fraction of ethylene glycol in a solution containing 20g by mass?

(a) 0.022

(b) 0.054

(c) 0.068

(d) 0.090

Answer 1

Answer : (c) 0.068

The molecular mass of ethylene glycol (C2H6O2) is  = (2×12) +(1×6) + (2×16) = 62 gm/mol.

The mass of ethylene glycol present in solution is 20 gm.

Moles of ethylene glycol = mass of ethylene glycol ÷ molecular mass of ethylene glycol

Moles of ethylene glycol = 20 ÷ 62 = 0.322 moles.

Mass of water = 100 – 20 = 80gm.

Thus, the number of moles of water = 80 ÷ 18 = 4.444 moles.

The mole fraction of ethylene glycol is 

        = 0.322 ÷ (0.322 + 4.444)

        = 0.068

c) 0.068