# In stoichiometry, what is molar mass used for?

In stoichiometry, molar mass is used to convert between the mass of a substance and how many moles of a substance.

#### Explanation:

For example: The molar mass of water is 18g/mol
Q: How many moles are there in a 4.5g sample of water?

$\frac{4.5 g {H}_{2} O}{1} x \frac{1 m o l {H}_{2} O}{18 g {H}_{2} O}$ = 0.25 mol ${H}_{2} O$

In both of the videos below, molar mass is used to convert between mass (g) and mole amounts of chemical substances.

Video from: Noel Pauller

Video from: Noel Pauller

Hope this helps!