How To Use Moles - Part 3

Watch the final part of the 'using moles' videos, to complete your understanding of the chemical calculations topic. Avogadro’s number describes what is known as 1 mole, or 12 g of carbon atoms. This is used in chemical calculations. For any element, the relative atomic mass is the weight in grams for one mole. When we compare chemicals, we compare equal numbers of particles, even though the weights are different. So if we have compounds instead of atoms, it doesn’t matter how many atoms are in the formula, only the number of compound particles. For any compound, the relative molecular mass (or Mr) is the weight in grams for one mole, or Avogadro's Number. The molecular mass of a compound is found by adding up the atomic masses ofall the elements that make it, multiplied by the number of times each atom appears. Moles say only how many particles there are, not how much is in them. The molecular mass units are grams per mole. We can work out how many moles we have by putting in the mass and rearranging. In chemistry, we use moles to work out how much of each reactant to weigh out. This means we can make sure we get enough product and none of the reactants are wasted. It also makes it easier to get the product pure.