Percentage COmposition of Compounds

The percentage composition of a compound represents the proportion of each element in a material, as a percentage of the total mass.
Calculating this figure involves dividing the total mass of each individual element by the overall mass of the compound, and then multiplying by 100.
An important base skill required to calculate the percentage composition of a compound is the ability to work out the relative formula mass (Mr) of a substance from a given chemical formula.
The process generally requires knowledge of the relative atomic masses (Ar) of each of the constituent elements, which can usually be found on the periodic table.
If a compound is made up of more than one atom of an element, ensure to multiply the atomic weight of that element by the number of atoms when calculating the total mass.
If a compound’s formula includes brackets, these indicate that there’s more than one atom of the compound inside them - these will need to be factored into the calculation as well.
Be sure to add together the masses of all the elements to find the total mass of the compound.
It’s crucial to remember that the sum of the percentage compositions of all the elements in a compound should always add up to 100%.
Understanding the percentage composition of a compound is vital for calculations involving empirical and molecular formulae.
Note: Real world samples might not precisely add up to 100% due to traces of other substances or small measurement errors.
Percentage composition calculations can also be used in stoichiometric calculations for reactions, giving an idea of how much of a reactant is needed or how much product can be expected from a given amount of reactant.
Finally, the calculations involving percentage composition are essential in determining the purity of samples in practical applications. Be aware of this context when revising for the Nature of Substances and Chemical Reactions.