All substances have an empirical formula. This is the simpliest whole ratio of atoms or ions of each element in a substance.Substances that are made of simple molecules also have a molecular formula..Relative formula mass(m sqaured) of a substance is the sum of the relative atomic mass(Ar) of all atoms or ions in its formula.

Steps for finding Empirical formulae

• Find masses
• look up given Ar values
• Divide masses by Ar
• Find the ratia

Steps for finding relative formula mass

• Write the formula of the compound.
• Write the numbers of each atom in the formula.
• Insert the relative atomic mass for each type of atom.
• Calculate the total mass for each element.
• Add up the total mass for the compound.

• When a solute is dissolved in a solvent to make a solution, the mass of the solution is equal to the mass of the solventand the mass of the solute.The mas overall mass of the substances does not change.  This is the law of conservation mass
• The amount of solute dissolved in a started volume of a solution is its concetration. 
• Concetration=mass of solute in g/ volume of solution in dm3
• If volume of the solution is given in cm3, convert it to dm3 by dividing by 1000cm3

Calculating product using formula masses

• Write the balanced chemical equation for the reaction.
• Work out the formula masses for the relevant substances and the number of molecules of each.
• Work out the ratio of reactant to product  for the required situation. (You want the unknown on the top!)
• Work out the ratio of reactant to product (or product to reactant) from the masses given.
• Write them equal to each other.
• Rearrange the equation and work out the answer.