[Pirt]

25cm³ of an aqueous solution of sodium molybdate, Na₂MoO₄, was diluted with 100³ with distilled water and treated carefully with potassium permanganate solution until a very faint pink colour persisted. The solution was then passed through a Jones reductor, and the eluated from the colum was collected directly into a solution of a fivefold excess of ferric alum in dilute sulphuric acid. This solution was then titrated with 0.1000 mol dm ^-3 KMnO₄ solution until a very faint pink end point was observed. The titre was 30.0cm³.

In the case of Mo, it was knon that passing a solution of Mo(VI) species through a jones reductor resulted in quantitative reduction to green Mo(III)

a) What was the purpose of treating the starting solution of sodium molybdate with a small amount of potassium permanganate before loading it onto the column?  (6marks)

For this question I was thinking if it had something to do with the oxidation states of Mo but was unsure, if the permanganate ions would oxidise the Mo to a suitable oxidation state so the when it passed through the jones reductor, it could reduce the Mo.

Was also wondering why the eluate from the colum was led directly into a solution of Fe³⁺ ions rather than simply titrated?

For this was thinking that it was because it could be reduced to a suitable oxidation state so that it could be oxidised by the KMnO₄.

Thanks