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Qualitative analysis of redox reactions
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Table 1:Ion (hydrated) +
VO2 (𝑎𝑞)
2+
𝑉𝑂 (𝑎𝑞)
3+
𝑉 (𝑎𝑞)
2+
𝑉 (𝑎𝑞)
Colour Yellow Blue Green Violet
Name Dioxovanadium Oxovanadium Vanadium (III) Vanadium (II)
(V) (IV)
Oxidation state +2 +3 +2
Table 2:
Test Observations
Dioxovanadium (V) + sulfite Yellow solution turned into a blue solution.
Dioxovanadium (V) + zinc Yellow solution turned into green solution
after 20 seconds, blue solution after 1 minute,
green solution after 7 minutes and violet
solution after 25 minutes.
Dioxovanadium (V) + iodide + thiosulfate Yellow solution turned orange after potassium
iodide was added and turned blue after
sodium thiosulphate was added.
Vanadium (II) + permanganate Purple solution turned green, blue, green,
yellow and violet with an increase of
permanganate added.
Questions:
1) The green color from the second test occurred because vanadium has many oxidation states.
When zinc was added to dioxovanadium, dioxovanadium oxidized to become vanadium (III)
which is green in color.
In which test(s) was vanadium reduced? Vanadium was reduced in test 2 when the green solution
of 20 seconds was changed to blue solution of 1 minute. Vanadium was also reduced in test 4
when the green solution of first drops changed to blue with added permanganate. Vanadium was
also reduced a few times in test 4.
In which test(s) was vanadium oxidized? Vanadium was oxidized in test 1, test 2 except for blue
solution, test 3 except for orange and test 4 a few times.
Which species is the stronger reducing agent: Sulphite or zinc? How do you know? Zinc is the
stronger reducing agent. In the test with sulphite, the yellow solution turned to blue which
indicates oxidation and this is the only experiment shared with us. In an experiment with zinc,
the green solution turned to blue which indicates reduction.
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