Chemistry

Relative Formula Mass is just the relative atomic masses Ar-(this is the same as mass number of an element) of all the atoms in the molecular formula added together

Eg:    Find the relative formula mass of MgCl2

Solution:  Look up the mass numbers of all the elements in this and add them up:     in this example you would do:  Mg + (2 x Cl) which is : 24 + (2 x 35.5) which is then equal to 95 so Mr pf MgCl2 is 95

You can find the % Mass of an Element in a Compound:

Percentage mass of an element in a compound= Ar x number of atoms of that element \ Mr of the compound 

EG: find the percentage mass of sodium in sodium carbonate Na2CO3---- 23 X 2 \ 106 X 100 = 43%