How to Convert Between Grams and Moles


When we convert between grams and moles we are converting between the mass of something to the number of that something. Most calculations in chemistry, like percent yield, require the number of atoms or molecules. The number of atoms or molecules is expressed in the unit of moles.

In order to convert from grams to moles you need to use the molar mass, which tells you much 1 mole of an element or molecule weighs in grams. The best method to perform the conversion is unit cancellation method.

Confused? Click here for an analogy to help explain the concepts.
Equations to know:

moles of substance = grams of substance/molar mass
Example Problem:

How many moles of CH4 are in 2.0 g of CH4?


Step 1

Find the molar mass of the molecule or atom.


Step 1

The molar mass of CH
4 is 16.05 g/mole.

For detailed instructions on calculating molar mass of CH4 click here.

Step 2

Using the unit cancellation method, convert from grams to moles.

Step 2