GCSE Chemistry · AQA 8462 · Topic 4.4.2
Reactions of acids
Key points
- Acids react with some metals to make a salt and hydrogen, e.g. magnesium + hydrochloric acid → magnesium chloride + hydrogen. (Higher: this is a redox reaction.)
- Acids are neutralised by alkalis (soluble hydroxides) and bases (insoluble hydroxides and metal oxides) to give a salt and water; with metal carbonates they give a salt, water and carbon dioxide.
- Hydrochloric acid makes chlorides, sulfuric acid makes sulfates and nitric acid makes nitrates.
- To make a soluble salt, add excess insoluble base or carbonate to the acid, filter off the excess, then crystallise the solution.
- Acids produce ions in water; alkalis produce ions. pH goes from 0–14 and can be measured with universal indicator or a pH probe.
- (Higher) Strong acids (hydrochloric, nitric, sulfuric) ionise completely; weak acids (ethanoic, citric, carbonic) only partly. Each decrease of 1 pH unit means the concentration is 10 times greater.
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Acids react in a small number of predictable ways, and each one makes a salt. This sub-topic covers those reactions, the pH scale, titrations and the difference between strong and weak acids, including two required practicals.
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