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Transition Metals

Ligand replacement in copper(II) complexes

  • 3 things to know
  • Unit A2 2

Overview

Shape of the hexaaquacopper(II) ion, shape of the [CuCl₄]²⁻ ion and seen when the ammonia is then added in excess.

What you need to know

Answer each one before you reveal it.

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Key term

What is the formula and colour of the complex formed when copper(II) sulfate dissolves in water?

Key term

What happens when concentrated hydrochloric acid is added to a solution of copper(II) sulfate in water?

Key term

Why does the coordination number fall from six to four when chloride ions replace water around copper(II)?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is the formula and colour of the complex formed when copper(II) sulfate dissolves in water?

    Model answer

    [Cu(H₂O)₆]²⁺, which is pale blue.

  2. 2

    What is the shape of the hexaaquacopper(II) ion?

    Model answer

    Octahedral.

  3. 3

    What happens when concentrated hydrochloric acid is added to that solution?

    Model answer

    The colour changes from pale blue to yellow or greenish yellow as the tetrachlorocuprate(II) ion forms.

  4. 4

    What is the shape of the [CuCl₄]²⁻ ion?

    Model answer

    Tetrahedral.

  5. 5

    Why does the coordination number fall from six to four?

    Model answer

    The chloride ion is much larger than a water molecule, so only four can fit around the copper ion.

  6. 6

    Why is concentrated rather than dilute hydrochloric acid used?

    Model answer

    A high concentration of chloride ions is needed to drive the equilibrium over in favour of the chloro complex.

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