Oxidation States of Vanadium

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In this demonstration, ammonium metavanadate (NH4VO3) is reduced using powdered zinc. This reaction takes place in acidic solution. This demonstration features on the AQA A-level specification. • This reaction occurs through a series of vanadium’s oxidation states. Each oxidation state has a different colour: +5 (VO2+ yellow); +4 (VO2+ blue 2:44); +3 (V3+ green 2:57) and +2 (V2+ violet 3:39). • The solution begins with a yellow colour (+5). When the powdered zinc is added, the solution immediately starts to go green and within a few seconds turns pale blue (+4). The short-lived green colour is a mixture of the yellow of +5 and the blue of +4. Over a further fifteen minutes or so, the colour of the solution changes first to green (+3) and eventually to violet (+2). The green colour of the +3 oxidation state is the most difficult to distinguish. This is pointed out in the video at 2:57. • Ammonium vanadate (NH4VO3) is a white solid at room temperature. When heated, it thermally decomposes to produce V2O5 (a yellow solid), NH3 and H2O. Vanadium pentoxide (V2O5) is an important catalyst in the Contact process for making sulfuric acid. • Interestingly, the name ‘vanadium’ comes from the Scandinavian goddess of beauty and fertility, Vanadís. The name was based on the wide range of colours found in vanadium compounds, as shown in this demonstration.

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