How do you calculate moles?

To calculate moles, begin by identifying the number of grams of the substance, and calculate its molar mass. Divide the number of grams by the molar mass of the compound to make the conversion to moles.

For example, suppose you need to convert 25 grams of Na2CO3 to moles. The periodic table lists the atomic weights of sodium, calcium and oxygen (to the nearest .1 grams/mole) as 23, 12 and 16, respectively. Multiplying each weight by its number of atoms {(23 x 2) + (12 x 1) + (16 x 3)} and adding the products together shows the compound's molar mass to be 106 grams/mole. Dividing 25 by 106 indicates an answer of 0.236 mol.