# Help with calculations using molar mass

1. Apr 4, 2017

### Grace Otto

So my chemistry teacher said that: Moles of a compound = mass of the sample (grams) ÷ molar mass of the compound (grams/mol)

So how do i get from there to the equations mol = g x (mol/g)??

I would like to know the steps involved i.e. rearranging the equation, dimensional analysis

Thanks!

2. Apr 4, 2017

### Staff: Mentor

What happens when you "÷ molar mass of the compound (grams/mol)" ?

3. Apr 4, 2017

### Ned Taylor

Im not sure exactly what your question is because it did not really make sense. But the meaning of that equation is to tell you the amount of moles that are in a certain quantity of a molecule. For example:
If there are 18 grams of carbon we can figure out how many moles there are by using the equation.

moles=amount/molar mass

That is, moles = 18/12
moles = 1.5
So there are 1.5 moles in 18 grams of carbon.
Good Luck from a fellow chem student

4. Apr 4, 2017

### vbrasic

The dimensional analysis is already done, right here, but I'll restate it in nicer format. $\frac{[g]}{[g/mol]}=[g]\frac{1}{[g/mol]}=[g][mol/g]=[mol]$. Note that dividing by a fraction is simply multiplication by it's reciprocal.