4.6 Neutralisation and the reactions of acids
How acids react with metals, metal oxides, metal hydroxides and metal carbonates, naming and writing formulae for salts, the ionic equation for neutralisation, and the tests for hydrogen and carbon dioxide.
AQA
Edexcel
OCR
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Neutralisation
Key terms
- Neutralisation: the reaction between an acid and a base to form a salt and water.
- Salt: a compound formed when the hydrogen in an acid is replaced by a metal (or ammonium).
In every neutralisation, hydrogen ions from the acid react with hydroxide ions from the alkali:
\mathrm{H^+}(aq) + \mathrm{OH^-}(aq) → H2O(l)
Four reactions to learn
| Reaction | Example |
|---|---|
| acid + metal → salt + hydrogen | Zn + 2HCl → ZnCl2 + H2 |
| acid + metal oxide → salt + water | CuO + H2SO4 → CuSO4 + H2O |
| acid + metal hydroxide → salt + water | NaOH + HCl → NaCl + H2O |
| acid + metal carbonate → salt + water + carbon dioxide | CaCO3 + 2HCl → CaCl2 + H2O + CO2 |
Naming salts
The first part of the name comes from the metal; the second part comes from the acid:
- hydrochloric acid makes chlorides
- sulfuric acid makes sulfates
- nitric acid makes nitrates
Example: magnesium oxide + nitric acid → magnesium nitrate + water.
Work out the formula from the ions: magnesium nitrate contains \mathrm{Mg^{2+}} and \mathrm{NO_3^-} ions, so it is Mg(NO3)2.
Testing the gases
- Hydrogen: hold a lit splint at the mouth of the test tube. Hydrogen burns with a squeaky pop.
- Carbon dioxide: bubble the gas through limewater (calcium hydroxide solution). It turns milky (cloudy).
Test yourself on this lesson
6 exam questions · 9 marks · with mark schemes and model answers
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