The particular salt produced in any reaction between an acid and a base or…

The idea

When an acid neutralises a base, alkali or carbonate, the salt formed is determined by two things: the acid's anion and the positive ion from the base, alkali or carbonate. Hydrochloric acid supplies Cl⁻ and gives chloride salts; nitric acid supplies NO₃⁻ and gives nitrates; sulfuric acid supplies SO₄²⁻ and gives sulfates. The positive ion comes from the metal or ammonium in the base, alkali or carbonate. For example, sodium hydroxide with hydrochloric acid gives sodium chloride; copper oxide with sulfuric acid gives copper sulfate; calcium carbonate with nitric acid gives calcium nitrate. Hydrogen ions from the acid combine with hydroxide ions to form water, or with carbonate ions to release carbon dioxide and water, while the remaining ions form the salt.

What earns the marks

• Identify the acid used and state the anion it provides: hydrochloric acid gives chloride ions (Cl⁻), nitric acid gives nitrate ions (NO₃⁻), sulfuric acid gives sulfate ions (SO₄²⁻).
• Identify the positive ion from the base, alkali or carbonate, such as Na⁺ from sodium hydroxide, Cu²⁺ from copper oxide, or NH₄⁺ from ammonium carbonate.
• Combine the correct positive and negative ions in the correct ratio so that the charges balance, for example two Na⁺ with one SO₄²⁻ gives Na₂SO₄.
• Name the salt by giving the positive ion name first and the acid-derived anion name second, for example sodium sulfate or ammonium nitrate.
• Write the salt formula using the formulae of common ions, ensuring subscripts show the ratio needed for electrical neutrality.
• Recognise that the reaction may also produce water, and carbon dioxide when a carbonate is used, but the salt is still determined by the acid and the positive ion.

Common mistakes and how to put them right

• Using the acid name unchanged in the salt name, such as saying hydrochloric acid produces sodium hydrochloric.

  Put it right: Use the anion-derived ending, so sodium chloride.

• Ignoring charge balance when writing formulae, such as writing NaSO₄ for sodium sulfate.

  Put it right: Use two sodium ions with one sulfate ion, giving Na₂SO₄.

• Assuming the positive ion comes from the acid rather than the base, alkali or carbonate.

  Put it right: Take the positive ion from the other reactant, for example Mg²⁺ from magnesium oxide.

• Forgetting that sulfuric acid produces sulfate salts, not sulfide or sulfite salts.

  Put it right: Link sulfuric acid specifically to the sulfate ion SO₄²⁻.

Exam tips

• Before naming a salt, write down the acid's anion and the positive ion from the other reactant, then combine them.
• Check the formula by adding up charges: the total positive charge must equal the total negative charge.
• If a carbonate is used, remember that carbon dioxide and water are also produced, but the question may only ask for the salt.
• Practise common ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Cu²⁺, Al³⁺, Cl⁻, NO₃⁻, SO₄²⁻ and CO₃²⁻ so you can deduce formulae quickly.