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Chemical Analysis, Organic Chemistry and Materials

Tests for metal ions and for ammonia

  • 3 things to know
  • Paper 2

Overview

The precipitates formed with sodium hydroxide solution by aluminium, calcium, copper, iron(II) and iron(III) ions, telling aluminium from calcium, the equation for copper(II) sulfate, and the tests for ammonium ions and ammonia gas with damp red litmus.

What you need to know

Answer each one before you reveal it.

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Key term

Describe the chemical test for ammonia gas, explain why damp red litmus is used, and name one property besides the litmus change.

Key term

What is seen when sodium hydroxide solution is added to a solution containing aluminium ions, Al³⁺?

Key term

What is seen when sodium hydroxide solution is added to a solution containing calcium ions, Ca²⁺?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is seen when sodium hydroxide solution is added to a solution containing aluminium ions, Al³⁺?

    Model answer

    A white precipitate forms, and it dissolves to leave a colourless solution when excess sodium hydroxide solution is added.

  2. 2

    What is seen when sodium hydroxide solution is added to a solution containing calcium ions, Ca²⁺?

    Model answer

    A white precipitate forms and it stays undissolved when excess sodium hydroxide solution is added.

  3. 3

    What is seen when sodium hydroxide solution is added to a solution containing copper ions, Cu²⁺?

    Model answer

    A blue precipitate forms.

  4. 4

    What is seen when sodium hydroxide solution is added to a solution containing iron(II) ions, Fe²⁺?

    Model answer

    A green precipitate forms.

  5. 5

    What is seen when sodium hydroxide solution is added to a solution containing iron(III) ions, Fe³⁺?

    Model answer

    A brown precipitate forms.

  6. 6

    Describe the test that shows a compound contains ammonium ions, NH₄⁺.

    Model answer

    Sodium hydroxide solution is added and the mixture is warmed, giving off ammonia gas that turns damp red litmus paper blue.

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