13012 14 Vanadium is a transition metal. (a) State what is meant by the term transition metal and explain using electronic configuration why vanadium is a transition metal. [2] (b) Complete the table below by giving the half-equations and the colour changes for the reduction reactions given. Reduction reaction Half-equation Colour change VO+ 2 to VO2+ VO2+ to V3+ V3+ to V2+ V3+ +  e- →  V2+ [5] 13012 [Turn over (c) V2+ is a powerful reducing agent and is oxidised by oxygen in the presence of acid to V3+. The half-equations with their standard electrode potentials are shown below. EO —/ V V3+(aq)  +  e-  ⇌  V2+(aq) - 0.26 O2(g)  +  4H+(aq)  +  4e-  ⇌  2H2O(l) + 1.23 (i) Write the ionic equation for the oxidation of V2+ using oxygen in the presence of acid. [2] (ii) Write the conventional cell representation for the cell which would be set up using the half cells associated with these two half-equations. [2] (iii) State and explain, in terms of electrons, which half cell is the negative electrode in the cell. [2] (iv) Calculate the emf of the cell. [1] 13012 [Turn over (d) Describe how you would set up a standard hydrogen electrode and use it to measure the standard electrode potential of VO+ 2(aq)/ VO2+(aq). In this question you will be assessed on using your written communication skills including the use of specialist scientific terms. [6] 13012 BLANK PAGE DO NOT WRITE ON THIS PAGE (Questions continue overleaf) [Turn over