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Year 11 - Science

Chemical tests: aqueous ions (including zinc)

Chemical analysis

Unit Summary

This unit covers tests to identify aqueous cations and anions, including flame tests for metal ions like lithium, sodium, and copper. It explains the benefits of instrumental analysis, such as sensitivity and accuracy, and focuses on interpreting results from charts, tables, and spectroscopy data.

Lesson Summary

You will learn to perform and interpret sodium hydroxide precipitate tests for metal ions and other tests for identifying ammonium, carbonate, sulfate, and halide ions.

Key Notes

  • 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.

Vocabulary To Learn

  • 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.

Common Mistakes To Avoid

  • All white precipitates in chemical tests indicate the presence of the same ion without the need for further testing.

3 Quick Questions (With Answers)

1. Explain the scientific idea in this lesson using two key 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.

2. Define this scientific word and use it in context. 'precipitate'

An insoluble solid formed when two solutions react together. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: All white precipitates in chemical tests indicate the presence of the same ion without the need for further testing. Correction: 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.

More Lessons In This Unit

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