Determination of molar mass

Exercise 3

   

A gaseous substance has at $765\;mmHg$ and $18^oC$ a volumetric mass of $2.10\frac{g}{L} $. Calculate the molar mass.

Let's take $1 \; L$ of that gas. ie $2.10 \; g$ : $p$ $=$ $\frac{765}{760}\; atm$ $n$ $=$ $\frac{p\;V}{R\; T} $ = $\frac{765\; 1 }{760\; 0.082 \; 291.15}$ = $0.042$ $M$ $=$ $\frac{m}{n}$ = $\frac{2.10}{0.042}$ = $50\; \frac{g}{mol}$