Copper is a transition element. It forms a wide variety of compounds.

1. (a)Define transition element. [1][1]
2. (b)An aqueous solution of copper(II) sulfate, CuSO₄, contains [Cu(H₂O)₆]²⁺ complex ions. If an excess of concentrated hydrochloric acid is added to this solution a ligand exchange reaction occurs and [CuCl₄]²⁻ complex ions are formed.
3. (b)(i)Complete Table 5.1 to state the geometry, the coordination number of copper, and one bond angle in each of the two complex ions. Table 5.1 complex ion | geometry | coordination number | bond angle [Cu(H₂O)₆]²⁺ | | | [CuCl₄]²⁻ | | | [3][3]
4. (b)(ii)In an isolated Cu²⁺ ion the d-orbitals are all degenerate. In a complex ion such as [Cu(H₂O)₆]²⁺ the d-orbitals are non-degenerate. Define degenerate and non-degenerate in this context. degenerate ............................................................................................................................... non-degenerate ........................................................................................................................... [1][1]
5. (b)(iii)Explain why the solutions of the two complex ions in Table 5.1 are different colours. [1][1]
6. (c)Cu²⁺ forms a complex ion containing water molecules and ethanedioate ions, C₂O₄²⁻, as ligands. The formula of the complex is [Cu(C₂O₄)₂(H₂O)₂]²⁻. The ethanedioate ion is a bidentate ligand.
7. (c)(i)Explain what is meant by bidentate. [1][1]
8. (c)(ii)There are three stereoisomers with the formula [Cu(C₂O₄)₂(H₂O)₂]²⁻. Complete the three-dimensional diagrams to show these three stereoisomers. stereoisomer 1 Cu stereoisomer 2 Cu stereoisomer 3 Cu [2][2]
9. (c)(iii)Use your answer to (c)(ii) to answer this question. Stereoisomers 1, 2 and 3 show two different types of isomerism. Name these two types of isomerism. For each type of isomerism identify the pair of stereoisomers that demonstrate this isomerism. type of isomerism | pair of stereoisomers | .............................................. and .............................................. | .............................................. and .............................................. [2][2]
10. (d)A solution contains 3.70g of Na₂[Cu(C₂O₄)₂(H₂O)₂] dissolved in 100cm³ of solution. A 25.0 cm³ sample of this solution is warmed and then oxidised by 0.0100 mol dm⁻³ acidified potassium manganate(VII). The equation for the redox reaction is shown. 5C₂O₄²⁻ + 2MnO₄⁻ + 16H⁺ → 10CO₂ + 2Mn²⁺ + 8H₂O Calculate the minimum volume of 0.0100 mol dm⁻³ acidified potassium manganate(VII) needed to oxidise all of the ethanedioate ions, C₂O₄²⁻, in the 25.0 cm³ sample. Show all your working. [Mᵣ: Na₂[Cu(C₂O₄)₂(H₂O)₂], 321.5] minimum volume = .............................................. cm³ [3][3]
11. (e)Copper(II) nitrate, Cu(NO₃)₂, and barium nitrate, Ba(NO₃)₂, both decompose when heated. Copper(II) nitrate decomposes at a lower temperature than barium nitrate. Suggest a reason for this difference. Explain your answer. [2][2]

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