Ethanol can be oxidised by heating with potassium dichromate(VI) in dilute sulfuric acid
4 marks · NormalState the initial colour of potassium dichromate(VI) solution before ethanol is added and heated.
Describe the colour change observed when ethanol is oxidised by heating with potassium dichromate(VI) in dilute sulfuric acid.
Name the ion that causes the final colour observed.
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(a) Orange
(b) The solution changes from orange to green when ethanol is oxidised.
(c) Cr3+ ion (chromium(III) ion)
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Marking points
B1 (a) · 1 mark · States the initial colour is orange.
B2 (b) · 1 mark · Mentions the colour changes to green.
B3 (b) · 1 mark · Describes it as a change from orange to green; not just final colour alone.
B4 (c) · 1 mark · Names the chromium(III) ion (Cr3+) as the cause of the green colour.
Worked solution
(a) The initial colour of potassium dichromate(VI) solution is orange.
(b) When ethanol is oxidised by potassium dichromate(VI) in dilute sulfuric acid, the colour changes from orange to green.
(c) The green colour is due to the Cr3+ ion (chromium(III) ion) formed during the reaction.