1.16 calculate relative formula masses (Mr) from relative atomic masses (Ar)

The Mr of a molecule or compound is calculated using this formula:

(Ar x number of that atom in molecule/compound) + (Ar x number of the other atom(s) if there are any)

e.g. Mr of HCL is (1 x 1) + (1 x 35.5) = 36.5

       Mr of H2O2 is (2 x 1) + (2 x 16) = 34