Vanadium is a transition element in Period 4 of the Periodic Table.

1. (a)Define transition element.[1]
2. (b)(i)State two other typical chemical properties of transition elements.[1]
3. (b)(ii)Explain why transition elements have variable oxidation states.[1]
4. (c)(i)In a titration, 25.00 cm³ of 0.0300 mol dm⁻³ VO2⁺(aq) is added to 10 cm³ of dilute sulfuric acid. A solution of 0.0400 mol dm⁻³ C2O4²⁻(aq) is then added from a burette until the end-point is reached. The titration is repeated and concordant results obtained, as shown in Table 3.1. volume of C2O4²⁻(aq) added/cm³ 1 28.15 2 28.10 Show that these results are consistent with the stoichiometry of equation 2.[2]
5. (c)(ii)An excess of C2O4²⁻ reacts with VO2⁺ to form a mixture of two octahedral complex ions. The complex ions are stereoisomers of each other. Each complex ion contains a V²⁺ cation and three C2O4²⁻ ions. Complete the diagram to show the three-dimensional structure of one of the complex ions. Include the charge of the complex ion. Use O to represent a C2O4²⁻ ion.[2]
6. (d)(i)Identify the vanadium species that forms when an excess of H2O2(aq) reacts with V²⁺(aq) under standard conditions. Explain your answer with reference to the data in Table 3.2.[1]
7. (d)(ii)Concentrated acidified H2O2 can react with V²⁺ to form red VO2³⁺ ions. VO2³⁺ contains vanadium combined with the peroxide anion, O2²⁻. Deduce the oxidation state of vanadium in VO2³⁺.[1]