# Explain how the relative formula mass of magnesium hydroxide, Mg(OH)₂, is determined from the relative atomic masses of its constituent elements, and state the relative formula mass of Mg(OH)₂. (Relative atomic masses: H = 1, O = 16, Mg = 24)

> Cambridge International IGCSE Chemistry (0620) — 3.2 Relative masses of atoms and molecules · Explain · 4 marks

## Mark scheme (4 marks)

1. Relative formula mass is found by adding together the relative atomic masses of all atoms in the formula
2. Correct identification that there are one Mg, two O, and two H atoms in Mg(OH)₂
3. Correct working: 24 + (2 × 16) + (2 × 1) OR 24 + 32 + 2
4. Relative formula mass of Mg(OH)₂ = 58

## Key terms

- [relative formula mass](https://www.gradenine.co.uk/glossary/relative-formula-mass)
- [relative atomic mass](https://www.gradenine.co.uk/glossary/relative-atomic-mass)

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