Question

A gas mixture contains 50% helium and 50% methane by volume. What is the percentage by mass of methane in the mixture?

• A. 18%
• B. 20%
• C. 50%
• D. 80%

Answer 1

The correct option is D 80%

For gases, molar and volume ratios are the same at a fixed temperature and pressure.
So,if the mixture contains 1 mole of $He$ and 1 mole of $C{H}_4.$
Mass of 1 mole of $C{H}_4=16$ g
Mass of 1 mole of $He$ = 4 g
Total mass of mixture = 20 g
Percentage by mass of $C{H}_4$
$=\frac{\text{mass of}C{H}_4}{\text{Total mass}}\times 100=\frac{16}{20}\times 100$
% mass of $C{H}_4$ = 80%