Relative Formula Mass

If you have a compound like MgCl2 then it has a relative formula mass, M, which is just the relative atomic masses of all the atoms in the molecular formula added together

Calculating relative formula mass is straight forward enough, but things can get a bit more confusing when you start working the

**percentage**compositions of compounds

Percentage mass of an element in a compounds = Ar x number of atoms of that element / Mr of the compounds x 100

These questions may involve recurring decimals but you will always have a calculator so you should be able to work it out

The relative formula mass of a substance made up of

**molecules**is the sum of the relative atomic masses of the atoms in the numbers shown in the**formula**.Relative formula mass has the symbol, Mr. To calculate the Mr for a substance:

work out how many atoms of each element there are in the chemical formula

add together the

*A*r values for all the atoms of each element present

If you have a compound like MgCl2 then it has a relative formula mass, M, which is just the relative atomic masses of all the atoms in the molecular formula added together

Calculating relative formula mass is straight forward enough, but things can get a bit more confusing when you start working the

**percentage**compositions of compounds

Percentage mass of an element in a compounds = Ar x number of atoms of that element / Mr of the compounds x 100

These questions may involve recurring decimals but you will always have a calculator so you should be able to work it out

The relative formula mass of a substance made up of

**molecules**is the sum of the relative atomic masses of the atoms in the numbers shown in the**formula**.Relative formula mass has the symbol, Mr. To calculate the Mr for a substance:

work out how many atoms of each element there are in the chemical formula

add together the

*A*r values for all the atoms of each element present