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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)