Transcript Oxidation states of vanadium

Oxidation states of vanadium
AH 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
Rules
1. Elements are 0
2. Atoms of monatomic ions have charge
of ion
3. O is -2 in most compounds
4. H is +1 in most compounds
5. F is -1 in all compounds
6. 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
5
4
3
2
Dioxovanadium(V)
Oxovanadium(IV)
Vanadium(III)
Vanadium(II)
Oxidation
state
Name
Summary of results
Test
Ammonium vandate +
acid
Observations
White solid turned red
and dissolved to a
yellow solution
Summary of reaction
VO3-  VO2+
(+5)  (+5)
Summary of results
Test
Vanadium(V) + zinc
Observations
The zinc effervesced
and the yellow solution
became green, blue,
green again and,
eventually, violet
Summary of reaction
VO2+  VO2+  V3+  V2+
(+5)  (+4)  (+3)  (+2)
Summary of results
Test
Vanadium(II) +
manganate(VII)
Observations
The violet solution
became green, blue,
green-yellow and,
finally, pink
Summary of reaction
V2+  V3+  VO2+ VO2+
(+2)  (+3)  (+4)  (+5)
Summary of results
Test
Vanadium(V) +
sulphite. Add
vanadium(II)
Observations
The yellow solution
became blue. On
adding vanadium(II)
the mixture became
green
Summary of reaction
VO2+  VO2+
(+5)  (+4)
VO2+ + V2+  V3+
(+4) + (+2)  (+3)
Summary of results
Test
Vanadium(V) + iodide
+ thiosulphate
Observations
The yellow solution
became a muddy
brown. Addition of
thiosulphate gave a
clear blue solution
Summary of reaction
VO2+  VO2+
(+5)  (+4)