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