Before the demonstration
Make up a 0.1 mol dm–3 solution of ammonium metavanadate by dissolving 11.7 g of solid in 900 cm3 of 1 mol dm–3 sulphuric acid and making up to 1 dm3 with deionised water. This yellow solution is usually represented as containing VO2+(aq) ions (dioxovanadium(V) ions) in which vanadium has an oxidation number of +5.