Molar mass is the mass of one mole of a substance, usually expressed in grams or kilograms. Let’s say you are conducting a laboratory exercise where you are required to measure 1 mole of sulfur. Can you see yourself counting out 6.02 x 10²³ atoms? If I have 1 mole of Iron, I would have 6.02 x 10²³ atoms. What would be the mass of 1 mole of Iron?

Since iron has an average atomic mass from the Periodic Table of 55.8 amu, the mass of 1 mole of iron would be 55.8 grams.

What happens with diatomic molecules like hydrogen?
1 mole of H2 is still 6.02 x 10²³ particles (in this case molecules) because they are joined by shared electrons.

One mole of H₂ would have a mass of 2 x 1.01g or 2.02 g/mole H₂ because mass is conserved.

The molar mass of a compound is found by taking the sum of the average atomic mass of each element times its subscript.

Example

1 mole of sodium carbonate (Na2CO3) would be:

2(22.99g) + 1(12.01g) + 3(15.99g) = 105.96 grams

Why?

Why do we need to know molar mass? What if you have a laboratory exercise which calls for 1 mole of manganese. You couldn't very well count out 602,000,000,000,000,000,000,000 (6.02 x10²³) atoms could you? But what you can do is measure out the amount of manganese, in grams, that will give you 6.02 x 10²³.