The molar mass of any substance is the mass of 1 mole of the substance. The molar mass id obtained by summing the masses of the component atoms. We also know that the molar mass is a whole number multiple of the empirical formula molar mass, the sum of the masses of all the atoms in the empirical formula.

Molar mass = empirical formula molar mass $\times$ n

For a particular compound, the value of n in both cases is the same. Therefore, we can find n by computing the ratio of the molar mass to the empirical formula molar mass.

n = $\frac{molar\ mass}{empirical\ formula\ molar\ mass}$

## Molar Mass Formula Problems

Some of the solved problems based on molar mass formula problems are given below:

Question 1: 2.9 g of a gas at 95oC occupied same volume as 0.184g of 2 at 17oC at the same pressure, what is the molar mass of the gas?
Solution:
Let molar mass of the gas be M

n = $\frac{2.9}{M}$

n = $\frac{0.184}{2}$ = 0.092

Volume of 0.092 moles of H2

= $\frac{0.092 \times R \times 290}{P}$ = $\frac{26.68R}{P}$

Volume of 29/M mole of gas

= $\frac{2.9 \times R\ 368}{MP}$

$\frac{1067.2R}{MP}$ = $\frac{26.68R}{P}$

M = 40 g/mol

Question 2: The density of certain gaseous oxide at 1.5 bar pressure at 10oC is same as that of dioxygen at 20oC and 4.5 bar pressure. Calculate the molar mass of gaseous oxide.
Solution:
Density of dioxygen (O2) at 4.5 bar pressure and 10oC

dO$_{2}$ = d$_{oxide}$

$\frac{4.5 \times 32}{R \times 283.15}$ = $\frac{1.5 \times M}{R \times 293.15}$

M = $\frac{4.5 \times 293.15 \times 32}{283.15 \times 1.5}$

M = 99.39 g/mol