• We have seen previously that the symbol for the relative atomic mass is?A_r
• This is calculated from the?mass number?and?relative abundances?of all the?isotopes?of a particular element
• The symbol for the?relative formula mass?is?M_r?and it refers to the?total mass?of the substance
• If the substance is molecular you can use the term?relative molecular mass, but this term should not be used for ionic compounds such as sodium chloride
• To calculate the?M_r?of a substance, you have to add up the?relative atomic masses?of all the atoms present in the formula

Relative Formula Mass Calculations Table

• In accordance with the Law of Conservation of Mass, the sum of the relative formula masses of the reactants will be the same as the sum of the relative formula masses of the products

Calculating percentage by mass of an element in a compound

• The percentage by mass of an element in a compound can be calculated using the following equation:

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