Question

A mixture has 18g water and 414g ethanol. The mole fraction of water in mixture is (assume ideal behaviour of the mixture).

• A. 0.1
• B. 0.4
• C. 0.7
• D. 0.9

Answer 1

Answer: (A)

0.1

Answer 2

Molecular weight of $\mathrm { C } _ { 2 } \mathrm { H } _ { 5 } \mathrm { OH } = 24 + 5 + 16 + 1 = 46$

Molecular mass of $\mathrm { H } _ { 2 } \mathrm { O } = 18$

414g of $\frac { 414 } { 46 } = 9$ mole

18g of $= \frac { 18 } { 18 } = 1$ mole

Mole fraction of water $= \frac { n _ { 1 } } { n _ { 1 } + n _ { 2 } } = \frac { 1 } { 1 + 9 }$ $= \frac { 1 } { 10 } = 0.1$