Iron is a transition element in the fourth period. Iron forms compounds containing the ions Fe²⁺ and Fe³⁺.

1. (a)(i)Define the term transition element.[1]
2. (a)(ii)Compare the melting point and density of iron with those of calcium, an s-block element in the fourth period. melting point density[1]
3. (a)(iii)Complete the electronic configuration of an isolated gaseous Fe²⁺ ion. 1s²[1]
4. (a)(iv)Aqueous Fe³⁺ ions form coloured complexes. Explain the origin of the colour in transition element complexes.[4]
5. (b)(i)State the shape of the [Fe(H₂O)₆]²⁺(aq) complex ion.[1]
6. (b)(ii)Write the equation for the reaction between [Fe(H₂O)₆]²⁺(aq) ions and an excess of CN⁻(aq) ions.[1]
7. (b)(iii)Deduce the oxidation states of iron in: [Fe(CN)₆]⁴⁻ [Fe(CN)NO]²⁻.[1]
8. (b)(iv)Define the term monodentate ligand.[2]
9. (b)(v)Complete the diagram to show the three-dimensional structure of the [Fe(CN)NO]²⁻ complex ion. [Figure 1.1][1]
10. (b)(vi)The two complex ions [Fe(CN)₆]⁴⁻ and [Fe(CN)₅NO]²⁻ are different colours. Explain why the colours of the two complex ions are different.[2]
11. (c)(i)Define the term coordination number.[1]
12. (c)(ii)E shows both optical isomerism and cis-trans isomerism. One isomer of E is shown. The C₂O₄²⁻ ion is represented as -ox/. In the boxes, draw three-dimensional diagrams to show: • the trans isomer of E • the optical isomer of E. [Figure 1.2][2]
13. (c)(iii)[Fe(C₂O₄)₂Cl₂]⁴⁻ contains ligands which are anions of ethanedioic acid, HO₂CCO₂H. Complete the table to show any observations for the reactions of HO₂CCO₂H with the named reagents. Where no change is observed, write 'none'. | reagent | observations with HO₂CCO₂H | |-----------------------------|---------------------------| | warm acidified manganate(VII) | | | 2,4-dinitrophenylhydrazine | | | warm Tollens' reagent | |[2]

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