Relative Formula (Molecular) Mass

  • The symbol for the relative atomic mass is Ar.
  • 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 Mr and it refers to the total mass of the molecule.
  • To calculate the Mr of a substance, you have to add up the relative atomic masses of all the atoms present in the formula.

Examples:

Relative Formula Table, IGCSE & GCSE Chemistry revision notes

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

Calculating % Mass of an Element in a Compound

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

percent of mass element equation, IGCSE & GCSE Chemistry revision notes

Example

calculating mass example_table, IGCSE & GCSE Chemistry revision notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.