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Chemistry of the D-Block Transition Metals

Colours and formulae of copper and cobalt complex ions

  • 3 things to know
  • Component 1

Overview

Coordination number and shape of [Cu(NH₃)₄(H₂O)₂]²⁺, colour of the [CuCl₄]²⁻ ion and oxidation state of the metal in [Cu(H₂O)₆]²⁺, [CuCl₄]²⁻ and [Cu(NH₃)₄(H₂O)₂]²⁺.

What you need to know

Answer each one before you reveal it.

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Key term

State how many ammonia molecules and how many water molecules are bonded to copper in the complex formed with excess ammonia.

Key term

Which cobalt complex ion is pink, and what is its coordination number?

Key term

Explain why [CuCl₄]²⁻ carries a negative charge while [Cu(H₂O)₆]²⁺ carries a positive one.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Give the formula of the approximately octahedral complex present in aqueous copper(II) sulfate.

    Model answer

    It is [Cu(H₂O)₆]²⁺.

  2. 2

    State how many ammonia molecules and how many water molecules are bonded to copper in the complex formed with excess ammonia.

    Model answer

    Four ammonia molecules and two water molecules, giving [Cu(NH₃)₄(H₂O)₂]²⁺.

  3. 3

    State the coordination number and shape of [Cu(NH₃)₄(H₂O)₂]²⁺.

    Model answer

    Its coordination number is six and its shape is approximately octahedral.

  4. 4

    Give the formula and charge of the tetrahedral copper chloro-complex.

    Model answer

    It is [CuCl₄]²⁻ and it carries a charge of 2−.

  5. 5

    State the colour of the [CuCl₄]²⁻ ion.

    Model answer

    It is yellow.

  6. 6

    Give the formula of the approximately octahedral aqueous cobalt(II) complex.

    Model answer

    It is [Co(H₂O)₆]²⁺.

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