Oxidation states of vanadiumAH Chemistry, Unit 1(c)

Aims

• Illustrate the presence of several oxidation states for vanadium

• Show how it is possible to change from one oxidation state to another

What are “oxidation states”?• The actual charge of an atom if the

atom is a monatomic ion, or the hypothetical charge assigned to an atom by certain rules

Rules1. Elements are 02. Atoms of monatomic ions have charge

of ion3. O is -2 in most compounds4. H is +1 in most compounds5. F is -1 in all compounds6. Sum of numbers in a compound is 0;

in a polyatomic ion is charge of ion

Example• Oxidation number of Cl in:

– HClO4 (perchloric acid)

– ClO3- (chlorate ion)

The significance of transition metals• Transition metals exhibit variable oxidation

states of differing stability• A change in oxidation state can bring about a

change in colour

Oxidation and reduction• Oxidation can be considered as an increase

in oxidation number

• Reduction can be considered as a decrease in oxidation number

• Compounds with metals in a high oxidation state tend to be oxidising agents whereas compounds with metals in a low oxidation state are often reducing agents

Oxidation states of vanadium

Ion (hydrated)

VO2+ VO2+ V3+ V2+

Colour Yellow Blue Green Violet

Oxidation state

5 4 3 2

Name Dioxovanadium(V) Oxovanadium(IV) Vanadium(III) Vanadium(II)

Summary of results

Test ObservationsSummary of

reaction

Ammonium vandate + acid

White solid turned red and dissolved to a yellow solution

VO3- VO2

+

(+5) (+5)

Summary of results

Test ObservationsSummary of

reaction

Vanadium(V) + zinc The zinc effervesced and the yellow solution became green, blue, green again and, eventually, violet

VO2+ VO2+ V3+ V2+

(+5) (+4) (+3) (+2)

Summary of results

Test ObservationsSummary of

reaction

Vanadium(II) + manganate(VII)

The violet solution became green, blue, green-yellow and, finally, pink

V2+ V3+ VO2+ VO2+

(+2) (+3) (+4) (+5)

Summary of results

Test ObservationsSummary of

reaction

Vanadium(V) + sulphite. Add vanadium(II)

The yellow solution became blue. On adding vanadium(II) the mixture became green

VO2+ VO2+

(+5) (+4)

VO2+ + V2+ V3+

(+4) + (+2) (+3)

Summary of results

Test ObservationsSummary of

reaction

Vanadium(V) + iodide + thiosulphate

The yellow solution became a muddy brown. Addition of thiosulphate gave a clear blue solution

VO2+ VO2+

(+5) (+4)