3.1.2

Relative Formula Mass

Test yourself

Calculating the Relative Formula Mass (Mr)

To calculate the relative formula mass of a compound, we need to know the relative atomic masses (Ar) of the elements that make the compound. Then we multiply the Ar values by the number of atoms of that element in the compound. Then we add these numbers together.

Illustrative background for E.g. hydrochloric acid (HCl)Illustrative background for E.g. hydrochloric acid (HCl) ?? "content

E.g. hydrochloric acid (HCl)

  • Identify the relative atomic mass (Ar) of each element in the compound:
    • Ar of hydrogen = 1
    • Ar of chlorine = 35.5
      • So, the total Mr of HCl is 1 + 35.5 = 36.5
Illustrative background for E.g. sulfuric acid (H<sub>2</sub>SO<sub>4</sub>)Illustrative background for E.g. sulfuric acid (H<sub>2</sub>SO<sub>4</sub>) ?? "content

E.g. sulfuric acid (H2SO4)

  • Identify the relative atomic mass (Ar) of each element in the compound:
    • Ar of hydrogen = 1
    • Ar of sulfur = 32
    • Ar of oxygen = 16
      • So, the total Mr of H2SO4 is (2x1) + (1x32) + (4x16) = 98

Jump to other topics

1Atomic Structure

2Chemical Bonding

3Quantitative Chemistry

4Chemical Changes

5Energy Changes

6The Rate & Extent of Chemical Change

7Organic Chemistry

8Chemical Analysis

9Chemistry of the Atmosphere

10Using Resources

Go student ad image

Unlock your full potential with GoStudent tutoring

  • Affordable 1:1 tutoring from the comfort of your home

  • Tutors are matched to your specific learning needs

  • 30+ school subjects covered

Book a free trial lesson