Question

A solution of ethanol in water is $10\%$ by volume. If density of the solution and pure ethanol are $0.9866$ g/mL and $0.785$ g/mL respectively, the mass percent will be:

• A. $7.55\%$
• B. $7.95\%$
• C. $8.55\%$
• D. $8.95\%$

Answer 1

The correct option is B $7.95\%$

The solution of ethanol in water is $10\%$ by volume means,
volume of solution = $100$ mL
$\therefore$ Volume of ethanol = $10$ mL
Weight of ethanol= volume $\times$ density
$\text{Weight of ethanol}=10\times 0.785=7.85g$
$\text{Weight of solution}=100\times 0.9866=98.66g$
$\therefore \text{Weight per cent}=\frac{7.85}{98.66}\times 100=7.95\%$