# Percentage COmposition of Compounds

Percentage Composition of Compounds

• A compound’s percentage composition is determined by the masses of its constituent elements, with regard to the entire mass of the compound.

• Learning to calculate the percentage composition is vital as it allows exploration of the proportional mass of each element in a compound.

• To calculate it, you first find the mass of each element in the formula, then divide this by the total mass of the compound, and finally multiply by 100 to convert to a percentage.

Calculating Percentage Composition

• First, determine the molar mass of each element in the compound, usually given in atomic mass units (amu).

• Then, calculate the total molar mass of the compound by adding up the molar masses of all the elements present.

• Divide the molar mass of each element by the total molar mass and multiply by 100 to get the percentage composition.

Example of Calculating Percentage Composition

• E.g. to determine the percentage composition of water (H2O), you calculate the molar mass of Hydrogen (H), Oxygen (O) and the total molar mass of water.

• The mass of Hydrogen is about 1 amu, and because there are two atoms of Hydrogen in one molecule of water, the total is 2 amu. The mass of Oxygen is 16 amu.

• Therefore, the total molar mass of water is 18 amu (2 for Hydrogen and 16 for Oxygen).

• The percentage composition of Hydrogen is (2/18) * 100 = 11.11% and for Oxygen is (16/18) * 100 = 88.89%.

Remember, the percentage composition of all elements in a compound will always add up to 100%.