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Qualitative Tests

Testing for the ammonium ion, sulfate and carbonate

  • 3 things to know
  • Unit AS 1

Overview

Test for the ammonium ion in a solid or solution, test for the sulfate ion and test for the carbonate ion.

What you need to know

Answer each one before you reveal it.

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Key term

Describe the test for the ammonium ion in a solid or solution.

Key term

Write the ionic equation for the reaction that occurs when the ammonium ion is tested with sodium hydroxide.

Key term

Why can the ammonium ion not be identified by a flame test?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Describe the test for the ammonium ion in a solid or solution.

    Model answer

    Sodium hydroxide solution is added and the mixture warmed, and the gas evolved turns damp red litmus paper blue.

  2. 2

    Write the ionic equation for the reaction that occurs when the ammonium ion is tested with sodium hydroxide.

    Model answer

    The equation is NH₄⁺(aq) + OH⁻(aq) → NH₃(g) + H₂O(l).

  3. 3

    Why must the mixture be warmed in the test for the ammonium ion?

    Model answer

    Warming drives the dissolved ammonia out of the solution so that enough gas escapes to be detected at the mouth of the tube.

  4. 4

    Why can the ammonium ion not be identified by a flame test?

    Model answer

    The flame test detects the light emitted by metal ions, and the ammonium ion contains no metal.

  5. 5

    Describe the test for the sulfate ion.

    Model answer

    Dilute hydrochloric acid is added and then barium chloride solution, and a white precipitate confirms a sulfate.

  6. 6

    Write the ionic equation for the formation of the precipitate in the sulfate test.

    Model answer

    The equation is Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s).

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