Chemistry Topic Practice

Relative Formula Mass (Mr) | GCSE Chemistry Practice

The relative formula mass of a compound is the sum of the relative atomic masses of the atoms in its formula.

Calculate the Mr of Calcium Carbonate (CaCO3).

What is Relative Formula Mass (Mr) | Practice?

"The sum of the relative atomic masses of the atoms in the numbers shown in the formula."

Question 1

Calculate the relative formula mass (Mr) of H2O. (H=1, O=16)

Question 2

Find the Mr of Ammonium Sulfate (NH4)2SO4. (N=14, H=1, S=32, O=16)

Question 3

Calculate the Mr of Mg(OH)2. (Mg=24, O=16, H=1)

Look up Relative Atomic Mass (Ar) on the periodic table.

Multiply Ar by the number of atoms of that element.

Sum all values together.

Exam Tip

Example: Mr of O2 is 16 + 16 = 32. Do not forget the "2"!

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