Mole

Objects do not need to have identical masses to be counted by weighing. All we need to know is the average mass of the objects.

To count the atoms in a sample of a given element by weighing, we must know the mass of the sample and the average mass for that element.

Samples in which the ratio of the masses is the same as the ratio of the masses of the individual atoms always contain the same number of atoms.

One mole of anything contains 6.0223 x 10^23 units of that substance.

A sample of an element with a mass equal to that element’s average atomic mass (expressed in grams) contains 1 mole of atoms.

The molar mass of any compound is the mass in grams of 1 mole of the compound.

The molar mass of a compound is the sum of the masses of the component atoms.

Moles of a compound = mass of the sample (g) x mol/g

Mass of a sample = moles of the sample x g/mol

Percent composition consists of the mass percent = (mass of a given element in a compound/mass of 1 mol of the compound) x 100