4.2.3Chemical Changes
Neutralisation of Acids and Salt Production — AQA GCSE Combined Science Trilogy 8464 - Chemistry Revision Notes & Topical Questions
5 min read 7 parts Lesson 8 of 18
Part 1 of 5Acids, bases and alkalis
Bases
- Bases A base is any substance that neutralises an acid.
- Typical bases are metal oxides, metal hydroxides and metal carbonates, and they have pH above 7 when in solution.
Alkalis
- Alkalis An alkali is a base that dissolves in water.
- Examples are sodium hydroxide, potassium hydroxide and calcium hydroxide solutions.
Insoluble bases
- Insoluble bases Many bases, such as copper(II) oxide and calcium carbonate, do not dissolve, so they are bases but not alkalis.
Part 2 of 5General word equations
| Reactants | Products |
|---|---|
| acid + metal oxide | salt + water |
| acid + metal hydroxide | salt + water |
| acid + metal carbonate | salt + water + carbon dioxide |
| acid + metal | salt + hydrogen |
Part 3 of 5Naming the salt
Salt name = metal from base + stem from acid
Hydrochloric acid
- Hydrochloric acid Forms chlorides, for example sodium chloride, NaCl.
Sulfuric acid
- Sulfuric acid Forms sulfates, for example copper(II) sulfate, CuSO4.
Nitric acid
- Nitric acid Forms nitrates, for example magnesium nitrate, Mg(NO3)2.
Source of the metal
- Source of the metal The first part of the salt's name is the metal in the oxide, hydroxide or carbonate.
Part 4 of 5Examples to learn
Metal oxides
- Metal oxides 2HCl + CuO → CuCl2 + H2O
- H2SO4 + Na2O → Na2SO4 + H2O
Metal hydroxides
- Metal hydroxides HCl + NaOH → NaCl + H2O
- H2SO4 + 2KOH → K2SO4 + 2H2O
Metal carbonates
- Metal carbonates 2HCl + CaCO3 → CaCl2 + H2O + CO2
- The carbon dioxide causes fizzing and turns limewater cloudy.
Part 5 of 5Writing a neutralisation equation
1
Identify the acid and the base, and decide which type of base it is.
2
Write the general word equation for that type of reaction.
3
Work out the salt from the acid's anion and the metal in the base.
4
Write the formulae and balance the symbol equation.
5
Add state symbols if asked: (aq) for solutions, (s) for solids, (l) for water and (g) for carbon dioxide.
Key terms
| Term | Meaning |
|---|---|
| Neutralisation | A reaction between an acid and a base that forms a salt and water. |
| Base | A substance that reacts with an acid to neutralise it. |
| Alkali | A base that is soluble in water, forming a solution with pH above 7. |
| Salt | An ionic compound formed when an acid's hydrogen is replaced by a metal ion. |
| Carbonate | A compound containing the CO32− ion that gives off carbon dioxide with acids. |
Avoid these mistakes
1
Forgetting that carbon dioxide is a third product when the base is a carbonate.
2
Saying all bases are alkalis; only soluble bases are alkalis.
3
Naming the salt after the acid's metal — acids contain hydrogen, so the metal comes from the base.
4
Not balancing equations such as H2SO4 + 2KOH, which need two hydroxide units.
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