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Relative Formula Mass

Chemistry: Edexcel IGCSE, topic 5.1.8

Relative Formula Mass (Mr)

The relative formula mass (Mr) of a substance is equal to the mass of 1 mole of that substance (in grams). For an element, this is the same as the relative atomic mass.

Carbon

Carbon

  • The mass of 1 mole of carbon is 12 g, which is the same as the relative atomic mass of carbon.
Carbon dioxide

Carbon dioxide

  • Every carbon dioxide molecule has 1 carbon atom and 2 oxygen atoms:
  • Ar of carbon = 12.
  • Ar of oxygen = 16.
    • Mr of carbon dioxide = 12 + (2 x 16) = 44.

Test yourself on Relative Formula Mass

  • The relative atomic mass sodium is 23. What is the mass of 1 mole of sodium?

  • The Ar of oxygen = 16. The Ar of hydrogen = 1. The Ar of carbon = 12. Which of the following Mr values is correct?

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