Starter quiz
- Which particle does an atom lose or gain one or more of to form an ion?
- proton
- electron ✓
- neutron
-
- What does litmus paper indicate?
- the concentration of ions in a solution
- the presence of metal ions
- whether a solution is acidic or basic ✓
- the pH value of a solution
-
- What is the charge of a cation?
- positive ✓
- negative
- neutral
-
- Which of the following is a common laboratory acid?
- ethanoic acid
- hydrochloric acid ✓
- carbonic acid
- citric acid
-
- Which of the following are basic laboratory techniques?
- heating solutions ✓
- performing chromatography ✓
- using a spectrometer
-
- What does a basic understanding of chemical reactions include?
- knowing how to write and balance chemical equations ✓
- understanding complex organic synthesis
- using advanced analytical techniques
-
Exit quiz
- What colour precipitate does copper(II) form with sodium hydroxide?
- blue ✓
- brown
- green
- yellow
-
- Which gas is released when ammonium ions are heated with sodium hydroxide?
- ammonia ✓
- hydrogen
- oxygen
- carbon dioxide
-
- What colour does damp red litmus paper turn in the presence of ammonia gas?
- purple
- green
- blue ✓
- it doesn't change colour
-
- What colour precipitate is formed when silver nitrate is added to a solution containing chloride ions?
- cream
- white ✓
- yellow
- grey
-
- Why is dilute nitric acid added before testing for halides?
- to enhance the colour of the precipitate
- to remove any carbonates that might interfere with the test ✓
- to neutralise the solution
- to form halide ions in solution
-
- What precipitate is formed when barium chloride is added to an acidified solution containing sulfate ions?
- green
- blue
- white ✓
- brown
-
Worksheet
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Lesson Details
Key learning points
- Some metal ions form coloured precipitates in a reaction with sodium hydroxide solution.
- Ammonium ions can be identified by heating with NaOH and using damp red litmus paper, which turns blue if positive.
- A dilute acid is usually added before testing for carbonates, sulfates or halides to avoid false positives.
- Halide ions produce different coloured precipitates when silver nitrate is added to a solution containing them.
- A white precipitate is formed when barium chloride is added to an acidified solution containing sulfate ions.
Common misconception
All white precipitates in chemical tests indicate the presence of the same ion without the need for further testing.
Explain that white precipitates can indicate different ions depending on the test. For instance, barium sulfate indicates sulfate ions, silver chloride indicates chloride ions, and sodium hydroxide tests distinguish between cations.
Keywords
Precipitate - An insoluble solid formed when two solutions react together.
Ion - An ion is an atom or group of atoms with a positive or negative charge due to the loss or gain of electrons.
Cation - A positively charged ion.
Anion - A negatively charged ion.
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