Question

Calculate the relative molecular mass[molecular weight]of 290 ml.of a gas 'A' at 17*C and 1520 mm pressure which weighs 2.73 g at s.t.p.[1 litre of hydrogen at s.t.p weighs 0.09 g.]

Answer 1

1. According to Avogadro's law :

Molecular mass = $\frac{MassofonemoleofgasatSTP}{2\times massofonehydrogenatomatSTP}$
2. Mass of one hydrogen atom at STP = $1.67\times {10}^{-24}g$
3. Also according to the same law :

$\frac{p_1{V}_1}{n_1{T}_1}=\frac{p_2{V}_2}{n_2{T}_2}=cons\tan t$

4. So,
n = $\frac{pV}{RT}=\frac{1520\times 290\times {10}^{-3}}{8.314\times 290}=0.182$
4. Mass of 0.182 moles is 2.73g
So,
Mass of 1 mole = $\frac{2.73}{0.182}=15g$
3. Molecular mass = $\frac{15}{2\times 1.67\times {10}^{-24}}g=111.11g$$\frac{15}{2\times 1.67\times {10}^{-24}}g=111.11g$