AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Reactions of acids with metals: Acids react with some metals to produce salts and hydrogen.
When an acid reacts with a metal, the metal displaces hydrogen from the acid.
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
When an acid reacts with a metal, the metal displaces hydrogen from the acid. The products are a salt and hydrogen gas. For example, magnesium reacts with hydrochloric acid: Mg + 2HCl → MgCl₂ + H₂. The salt formed depends on the acid used: hydrochloric acid gives chloride salts, sulfuric acid gives sulfate salts, and nitric acid gives nitrate salts. The metal must be more reactive than hydrogen for the reaction to occur; metals such as copper, silver and gold do not react with dilute acids. Hydrogen gas is identified by a squeaky pop with a lit splint. For Higher Tier students, this reaction is a redox process: the metal is oxidised (loses electrons) and hydrogen ions are reduced (gain electrons).
What earns the marks
- State the general word equation: acid + metal → salt + hydrogen.
- Name the salt produced from the specific acid and metal, for example magnesium + hydrochloric acid → magnesium chloride + hydrogen.
- Write a balanced symbol equation, including state symbols where appropriate, for example Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g).
- Explain that the metal must be more reactive than hydrogen for the reaction to occur, and that less reactive metals such as copper do not react with dilute acids.
- Describe the test for hydrogen gas: a lit splint produces a squeaky pop.
- Identify the reaction as a redox process in which the metal is oxidised and hydrogen ions are reduced (HT only).
Common mistakes and how to put them right
Writing the salt as the metal name only, for example 'magnesium' instead of 'magnesium chloride'.
Put it right: The salt name combines the metal and the acid's negative ion.
Forgetting to balance the equation, especially the hydrogen molecules.
Put it right: Ensure H₂ is written and the equation balances for both atoms and charge.
Assuming all metals react with acids.
Put it right: Check reactivity; copper, silver and gold do not react with dilute acids because they are less reactive than hydrogen.
Exam tips
- Learn the salt names for the three common acids: hydrochloric → chloride, sulfuric → sulfate, nitric → nitrate.
- When writing symbol equations, balance the metal atoms first, then the hydrogen atoms, and finally check the non-metal atoms.
Try the lesson
The start of the Reactions of acids with metals: Acids react with some metals to produce salts and hydrogen. lesson, made from checked teaching notes for this specification point.
Have a go first
Which gas is produced when magnesium reacts with hydrochloric acid?
Listen
When an acid reacts with a metal, the metal displaces hydrogen from the acid. The products are a salt and hydrogen gas. For example, magnesium reacts with hydrochloric acid: Mg + 2HCl → MgCl₂ + H₂. The salt formed depends on the acid used: hydrochloric acid gives chloride salts, sulfuric acid gives sulfate salts, and nitric acid gives nitrate salts. The metal must be more reactive than hydrogen for the reaction to occur; metals such as copper, silver and gold do not react with dilute acids. Hydrogen gas is identified by a squeaky pop with a lit splint. For Higher Tier students, this reaction is a redox process: the metal is oxidised (loses electrons) and hydrogen ions are reduced (gain electrons). A strong answer earns marks for these points. State the general word equation: acid + metal → salt + hydrogen. Name the salt produced from the specific acid and metal, for example magnesium + hydrochloric acid → magnesium chloride + hydrogen. Write a balanced symbol equation, including state symbols where appropriate, for example Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g). Explain that the metal must be more reactive than hydrogen for the reaction to occur, and that less reactive metals such as copper do not react with dilute acids. Exam tip: Learn the salt names for the three common acids: hydrochloric → chloride, sulfuric → sulfate, nitric → nitrate.
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Key words
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Acid–metal reactions as displacement reactions
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Salt formation and naming from the parent acid
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Reactivity series and the position of hydrogen
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See every definition
- Acid–metal reactions as displacement reactions
- When an acid reacts with a metal, the metal displaces hydrogen from the acid, producing a salt and hydrogen gas.
- Salt formation and naming from the parent acid
- The salt formed depends on the acid used: hydrochloric acid gives chloride salts, sulfuric acid gives sulfate salts, and nitric acid gives nitrate salts.
- Reactivity series and the position of hydrogen
- The metal must be more reactive than hydrogen for the reaction to occur, so metals such as copper, silver and gold do not react with dilute acids.
Label the diagram
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