How to Calculate the Number of Moles

Question: How many moles are in 1000 g of sucrose?

1. Obtain the atomic mass

First, write down the formula for sucrose: C₁₂H₂₂O₁₁

The formula tells us there are 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms.

Look for the atomic mass of each element present in the compound from the periodic table.

Organize your calculations neatly to show how to calcualte the sum of the atomic masses of the compound’s constituent atoms.

Element	Symbol	Atomic mass (amu)	#n atoms	Mass
Hydrogen	H	1.008	22	22(1.008) = 22.176 amu
Carbon	C	12.01	12	12(12.01) = 144.12 amu
Oxygen	O	16.00	11	11(16.00) = 176.00 amu
				Molecular mass of sucrose = (22.176 + 144.12 + 176.00) = 342.296 amu

The molar mass of sucrose is simply the molecular mass expressed as g/mol.

Molar mass of sucrose = 342.296 g/mol

Apply the formula to calculate the number of moles

The answer can be rounded to 3 mol.

(Note: The symbol for mole is “mol”)

Knowing the number of moles allows you to calculate the number of atoms if you are dealing with chemical compounds.
Moles are very useful, they allow chemists to use chemical equations to determine the mass of reactants and products.