Question

A solution of ethanol in water is 10% by volume. If the solution and pure ethanol have densities $0.9866gm{l}^{-1}$ and $0.785gm{l}^{-1}$ respectively. The percentage of ethanol by weight is about:

• A. 7
• B. 8
• C. 9
• D. 10

Answer 1

The correct option is B 8

Weight of ethanol $=Volume\times density=10\times 0.785=7.85g$

Weight of solution $=Volume\times density=100\times 0.9866=98.66g$

Percentage weight $=\frac{\text{Weight of ethanol}}{\text{Weight of solution}}=\frac{7.85}{98.66}\times 100=7.95\%\simeq 8.0\%$

Hence, option B is correct.