Ammonia has the formula NH₃. Ammonium sulfate has the formula (NH₄)₂SO₄. Ammonium sulfate is formed when ammonia reacts with sulfuric acid, H₂SO₄. Write the balanced symbol equation for this reaction and state the empirical formula of ammonium sulfate.

Pearson Edexcel International GCSE Chemistry (4CH1) — 1.5 Chemical formulae, equations and calculations · State · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Ammonium sulfate is widely used as a fertiliser. It is manufactured by reacting ammonia gas with sulfuric acid.

Model answer (4 marks)

2NH₃ + H₂SO₄ → (NH₄)₂SO₄
Empirical formula: N₂H₈SO₄

Omitting the coefficient 2 in front of NH₃, giving an unbalanced equation.
Writing the empirical formula as NH₄SO₄ instead of N₂H₈SO₄.
Using the formula unit (NH₄)₂SO₄ as the empirical formula without simplifying to N₂H₈SO₄.

Correct reactants and products written: NH₃ + H₂SO₄ → (NH₄)₂SO₄
Equation correctly balanced with a 2 in front of NH₃: 2NH₃ + H₂SO₄ → (NH₄)₂SO₄
Correct identification of atoms in one formula unit of (NH₄)₂SO₄: N₂H₈SO₄ (2 N, 8 H, 1 S, 4 O)
Correct empirical formula of ammonium sulfate stated as N₂H₈SO₄ (already the simplest whole number ratio, so empirical formula = N₂H₈SO₄ / equivalent correct simplest ratio accepted)