If $200$ $cm^3$ of a gas have a mass of $0.268$ g in normal conditions, calculate its molar mass.
$n=\frac{m}{M}$ Normal conditions: $0^oC$ 1 atm
$n=$ $\frac{PV}{RT}$ $=$ $\frac{1\cdot 0.2}{0.082\cdot 273.15}$ $M$ $=$ $\frac{m}{n}$ $=$ $\frac{0.268\cdot 0.082\cdot 273.15}{1\cdot 0.2}$ $=$ $30.0\frac{g}{mol}$
