Question

If the weight of $5.6$ litres of a gas at S.T.P is $11$ grams, the gas is:

• A. Phosphine
• B. Phosgene
• C. Nitric oxide
• D. Nitrous oxide

Answer 1

Answer: (D)

Nitrous oxide

At S.T.P. 1 mole of a gas occupies a volume of 22.4 liters. Its mass will be equal to its molar mass.
The weight of 5.6 liters of a gas at S.T.P is 11 grams.
The weight of 22.4 litres of a gas at S.T.P will be 44 grams,

$11g\times \frac{22.4}{5.6}=44g$
The molar mass of nitrous oxide
$\left(N_{2}O\right)$ is $14+14+16=44g/mol$.
Hence, the gas is nitrous oxide
$\left(N_{2}O\right)$.
Note: The molecular weight of phosphine $P{H}_3$, phosgene $COC{l}_2$ and nitric oxide $NO$
are 34 g/mol, 99 g/mol and 30 g/mol respectively.