AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Soluble salts can be made from acids by reacting them with solid insoluble…
Full specification wording
Soluble salts: Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates.
A soluble salt can be prepared by reacting an acid with an insoluble solid.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 1 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A soluble salt can be prepared by reacting an acid with an insoluble solid. The solid may be a metal, a metal oxide, a metal hydroxide or a metal carbonate. The acid dissolves the solid and a salt forms in solution. For example, copper oxide reacts with sulfuric acid to make copper sulfate, and magnesium reacts with hydrochloric acid to make magnesium chloride. The method works because the solid is insoluble, so it can be added in excess and then removed by filtration. The reaction stops when no more solid dissolves. The resulting solution contains the soluble salt, which can be crystallised. This is a key preparation method for soluble salts in the laboratory.
What earns the marks
- Choose an insoluble solid reactant that contains the required positive ion, such as a metal, metal oxide, metal hydroxide or metal carbonate.
- Choose the correct acid to supply the required anion, for example hydrochloric acid for a chloride salt or sulfuric acid for a sulfate salt.
- Add the solid to the acid and observe the reaction, which may produce bubbles if a carbonate is used or heat if a metal reacts.
- Continue adding the solid until no more dissolves or reacts, showing that the acid has been neutralised.
- Filter the mixture to remove the excess insoluble solid and collect the solution containing the soluble salt.
- Obtain the solid salt from the solution by evaporation or crystallisation.
Common mistakes and how to put them right
Choosing a soluble solid such as sodium hydroxide when the method requires an insoluble solid.
Put it right: Use an insoluble base such as copper oxide or an insoluble carbonate.
Adding too little solid so that acid remains.
Put it right: Add solid until no more reacts, then filter off the excess.
Filtering before the reaction is complete, which leaves unreacted acid in the solution.
Put it right: Wait until no further reaction occurs before filtering.
Using a metal that reacts dangerously or not at all, such as sodium, instead of a suitable metal like magnesium.
Put it right: Select a metal that reacts safely and is appropriate for the salt required.
Exam tips
- State clearly that the solid must be insoluble so it can be removed by filtration.
- Describe adding the solid in excess until no more reacts, then filtering to remove the excess.
- Link the choice of solid to the positive ion needed in the salt and the choice of acid to the negative ion needed.
- Mention crystallisation or evaporation as the final step to obtain the solid salt.
Try the lesson
The start of the Soluble salts: Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following is a solid insoluble substance that can be reacted with dilute sulfuric acid to prepare a sample of a soluble salt?
Listen
A soluble salt can be prepared by reacting an acid with an insoluble solid. The solid may be a metal, a metal oxide, a metal hydroxide or a metal carbonate. The acid dissolves the solid and a salt forms in solution. For example, copper oxide reacts with sulfuric acid to make copper sulfate, and magnesium reacts with hydrochloric acid to make magnesium chloride. The method works because the solid is insoluble, so it can be added in excess and then removed by filtration. The reaction stops when no more solid dissolves. The resulting solution contains the soluble salt, which can be crystallised. This is a key preparation method for soluble salts in the laboratory. A strong answer earns marks for these points. Choose an insoluble solid reactant that contains the required positive ion, such as a metal, metal oxide, metal hydroxide or metal carbonate. Choose the correct acid to supply the required anion, for example hydrochloric acid for a chloride salt or sulfuric acid for a sulfate salt. Add the solid to the acid and observe the reaction, which may produce bubbles if a carbonate is used or heat if a metal reacts. Continue adding the solid until no more dissolves or reacts, showing that the acid has been neutralised. A common slip: Choosing a soluble solid such as sodium hydroxide when the method requires an insoluble solid. Instead, use an insoluble base such as copper oxide or an insoluble carbonate. Exam tip: State clearly that the solid must be insoluble so it can be removed by filtration.
See it
Put it in order
Put these steps in the order they happen.
- 1. Obtain solid salt by evaporation or crystallisation
- 2. Collect solution containing soluble salt
- 3. Add solid to acid and observe reaction
- 4. Filter mixture to remove excess insoluble solid
- 5. Choose insoluble solid containing required positive ion
- 6. Choose acid to supply required anion
- 7. Continue adding solid until no more dissolves or reacts
Key words
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Preparing soluble salts
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Acid reactions with insoluble bases
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Excess solid method
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Filtration and crystallisation
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See every definition
- Preparing soluble salts
- A soluble salt can be prepared by reacting an acid with an insoluble solid, which dissolves the solid and forms a salt in solution.
- Acid reactions with insoluble bases
- The solid may be a metal, a metal oxide, a metal hydroxide or a metal carbonate, and the acid dissolves the solid so a salt forms in solution.
- Excess solid method
- Because the solid is insoluble, it can be added in excess and then removed by filtration, and the reaction stops when no more solid dissolves.
- Filtration and crystallisation
- The mixture is filtered to remove the excess insoluble solid and collect the solution containing the soluble salt, which can be crystallised.
Label the diagram
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1Box 1
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3Box 3
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