JOURNAL #72How many moles of compound

are there in 6.00g of ammonium sulfate?

How many molecules are there in 20.0g sulfuric acid?

TODAY WE WILL CALCULATE PERCENTAGE COMPOSITION

PERCENTAGE COMPOSITION It is useful to know the percentage by

mass of a particular element in a chemical compound

This is called percentage composition. For example: suppose the compound

potassium chlorate were to be used as a source of oxygen. It would be helpful to know the percentage of oxygen in the compound.

PERCENTAGE COMPOSITION To find the mass percentage of an element in a

compound, you divide the mass of the element in the sample by the total mass of the sample. Then, multiply this value by 100.

Mass of element in sample of compoundMass of sample of compound X 100 = % element in compound

EXAMPLES: Calculate the percentage composition

of copper (I) sulfide.

Calculate the percentage composition of sodium nitrate

EXAMPLES: Calculate the percentage composition

of lead (II) chloride

Calculate the percentage composition of barium nitrate

EXAMPLE:As some salts crystallize from a water solution, they bind water molecules in their crystal structure. Sodium carbonate forms such a hydrate, in which 10 water molecules are present for every formula unit of sodium carbonate. Find the mass percentage of water in

sodium carbonate decahydrate, NaCO3 ● 10H20, which has a molar mass of 286.19g/mol.