Neutralisation of acids and salt production — AQA GCSE Chemistry
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Neutralisation of acids and salt production explained
Neutralisation of acids and salt production covers 3 specification points, including Acids are neutralised by alkalis (eg soluble… and The acid used (hydrochloric acid produces….
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Open a point below for its explanation and revision guidance.
Acids are neutralised by alkalis (eg soluble metal hydroxides) and bases (eg insoluble metal hydroxides and metal oxides) to produce salts and water, and by metal carbonates to produce salts, water and carbon dioxide.
Neutralisation occurs when an acid reacts with a base, producing a salt and water. Alkalis are soluble bases, such as sodium hydroxide, while insoluble bases include copper(II) oxide and copper(II) hydroxide. For example, hydrochloric acid with sodium hydroxide gives sodium chloride and water: HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l). With an insoluble base such as copper(II) oxide, the reaction is CuO(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l). Metal carbonates also neutralise acids but produce carbon dioxide as well as salt and water, for example CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). The salt name comes from the metal and the acid: hydrochloric acid gives chlorides, sulfuric acid gives sulfates, nitric acid gives nitrates.
The particular salt produced in any reaction between an acid and a base or alkali depends on: the acid used (hydrochloric acid produces chlorides, nitric acid produces nitrates, sulfuric acid produces sulfates) the positive ions in the base, alkali or carbonate.
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.
Students should be able to: predict products from given reactants use the formulae of common ions to deduce the formulae of salts. AQA GCSE Chemistry 8462. GCSE exams Jun
This practical skill requires you to look at the reactants in a neutralisation or acid-carbonate reaction and work out what products form. First identify the acid and the other reactant. The acid provides the anion for the salt: chloride from hydrochloric acid, nitrate from nitric acid, or sulfate from sulfuric acid. The other reactant provides the positive ion, such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Cu²⁺, Al³⁺ or NH₄⁺. Then combine these ions in the ratio that balances charge to write the salt formula. For example, aluminium oxide with hydrochloric acid gives aluminium chloride, AlCl₃, because three Cl⁻ balance one Al³⁺. Water is also produced, and carbon dioxide is produced if the reactant is a carbonate. Always check that the formula is electrically neutral.
Your focus
- Write word and balanced symbol equations for neutralisation reactions.
- Name the salt formed from a given acid and base or carbonate.
- Describe the test for carbon dioxide produced in acid-carbonate reactions.
Show all 9 objectives
- Predict the salt produced when a named acid reacts with a named base, alkali or carbonate.
- Deduce the formula of a salt from the formulae of its positive and negative ions.
- Explain how the acid and the positive ion together determine the identity of the salt.
- Predict the products of reactions between named acids and named bases, alkalis or carbonates.
- Use the formulae and charges of common ions to deduce the formula of a salt.
- Write balanced formulae for salts by ensuring the total positive and negative charges are equal.
Neutralisation of acids and salt production exam tips
Marking Points
- Name the salt produced from the metal and the acid used.
- Write balanced symbol equations for neutralisation with an alkali, a base and a metal carbonate.
- State that neutralisation of an acid with an alkali or base produces a salt and water only.
- State that reaction with a metal carbonate also produces carbon dioxide.
- Describe the test for carbon dioxide using limewater turning milky or cloudy.
- 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.
- Identify the acid and the other reactant from their names or formulae.
- State the anion supplied by the acid: Cl⁻, NO₃⁻ or SO₄²⁻.
- State the positive ion supplied by the base, alkali or carbonate, including its charge.
- Combine the ions in the simplest whole-number ratio that gives zero overall charge, and write the salt formula with correct subscripts.
- Name the salt using the positive ion name followed by the modified acid anion name.
- State the other products: water always, and carbon dioxide when a carbonate reacts with an acid.
Examiner Tips
- 💡Write the word equation first to confirm all products before balancing the symbol equation.
- 💡Include state symbols where the question requires a full equation.
- 💡Link the limewater test directly to carbon dioxide and describe the colour change clearly.
- 💡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.
- 💡Underline the acid and the other reactant in the question before you start predicting products.
- 💡Write the ions with their charges above the reactants to help you balance the salt formula.
- 💡Check that the sum of positive charges equals the sum of negative charges in your final salt formula.
- 💡If the question asks for products, include the salt, water, and carbon dioxide if a carbonate is present.
Common Mistakes
- Omitting water from the products of an acid-carbonate reaction; the correction is that the products are salt, water and carbon dioxide.
- Naming the salt from the acid alone; the correction is to combine the metal name with the acid-derived ending, such as sodium sulfate.
- Treating all bases as soluble; the correction is that alkalis are soluble bases while many metal oxides and hydroxides are insoluble bases.
- Using the acid name unchanged in the salt name, such as saying hydrochloric acid produces sodium hydrochloric; the correction is to use the anion-derived ending, so sodium chloride.
- Ignoring charge balance when writing formulae, such as writing NaSO₄ for sodium sulfate; the correction is to 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; the correction is to 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; the correction is to link sulfuric acid specifically to the sulfate ion SO₄²⁻.
- Writing the salt formula without balancing charges, such as AlCl for aluminium chloride; the correction is AlCl₃ because three chloride ions balance one aluminium ion.
- Mixing up the endings for salts from different acids, such as calling a nitrate a nitride; the correction is to use -ate endings for these common oxyacids and -ide for hydrochloric acid.
- Forgetting to include water as a product of neutralisation; the correction is to remember that hydrogen ions and hydroxide ions form water, and carbonate reactions also release carbon dioxide.
- Using the formula of the acid as the formula of the salt, such as writing H₂SO₄ for a sulfate salt; the correction is to replace the hydrogen ions with the positive ion from the base.