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Question 13

A chemist performed a series of qualitative tests on an unknown solid, Y, to determine the ions present. The observations were recorded as follows:

  • Test 1: A flame test on solid Y produced a brick-red flame.
  • Test 2: Solid Y was dissolved in deionised water to form a solution, which was split into three separate test tubes, labelled D, E, and F.
    • To test tube D, dilute sodium hydroxide solution was added dropwise, resulting in a dirty-green precipitate.
    • To test tube E, dilute nitric acid was added followed by silver nitrate solution, resulting in a cream precipitate.
    • To test tube F, dilute hydrochloric acid was added followed by barium chloride solution, which resulted in no visible reaction.
a.

Identify the ion responsible for: (i) the brick-red colour in the flame test; (ii) the dirty-green precipitate formed with dilute sodium hydroxide; (iii) the cream precipitate formed with silver nitrate solution.

[3]
b.

Describe how the chemist should carry out a flame test on solid Y to ensure reliable results.

[3]
c.

(i) Why was dilute nitric acid added to test tube E before adding the silver nitrate solution? (ii) Why should dilute hydrochloric acid not be used in place of dilute nitric acid in this test?

[3]
d.

Suggest one common anion that cannot be identified using precipitation reactions because all of its common salts are soluble.

[1]

Chemical tests Questions

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