6CH05/01 june 2013

Can someone explain the answer to question 6 in this paper please

If you mean the equilibrium with the metal aqua complex with a charge of +n, I get C as the answer.

A is wrong, as the water is accepting a proton from the complex, so it is acting as a base.

B is wrong, as the more charged the central ion is, the more polarising it is and the more easily it breaks the O-H bonds in the surrounding water ligands, releasing more H^+ ions into the solution. If n were 2 and not 3, it would release less H^+ ions, so the pH would be greater.

D is wrong, as the reaction is not a redox reaction- the oxidation states of O and H are unchanged, so the oxidation state of M will also have to be unchanged. The charge on the complex is only decreased by 1, since one of the neutral H2O ligands has deprotonated to a hydroxide ligand, OH^-.

C is correct, because for the same reasons as why B is wrong, when n = 3, the ion is more polarising and the breakage of the O-H bonds is more favourable compared to when n = 2.