How do you calculate moles from mass?

To calculate moles from mass, you divide the mass of the substance by its molar mass.

The concept of moles is a fundamental one in chemistry. It's a way of counting atoms or molecules in a substance. The mole is the SI unit for the amount of a substance, and it's defined as the amount of a substance that contains as many entities (atoms, molecules, ions etc.) as there are in 12 grams of carbon-12. This number is known as Avogadro's number, and it's approximately 6.022 x 10^23.

To calculate the number of moles from the mass of a substance, you need to know the molar mass of that substance. The molar mass is the mass of one mole of a substance, and it's usually given in grams per mole (g/mol). You can find the molar mass of an element from the periodic table: it's the atomic weight of the element expressed in g/mol. For a compound, you add up the molar masses of all the elements in the compound.

Once you have the molar mass, you can calculate the number of moles by dividing the mass of the substance by the molar mass. This is because the molar mass is the mass of one mole of the substance, so if you know the mass of the substance, you can find out how many moles it represents by dividing the mass by the molar mass.

For example, if you have 18 grams of water (H2O), and the molar mass of water is approximately 18 g/mol (16 for oxygen and 1 for each hydrogen), you would calculate the number of moles as follows: 18 g ÷ 18 g/mol = 1 mole. This means that 18 grams of water is equivalent to 1 mole of water.