Ethanol can be oxidised by heating with potassium dichromate(VI) in dilute sulfuric acid
2 marks · HardExplain why dilute sulfuric acid must be present when potassium dichromate(VI) is used to oxidise ethanol. Include in your answer the role that the acid plays in the reaction.
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Dilute sulfuric acid provides the H+ ions that allow potassium dichromate(VI) to act as an oxidising agent. Without the acid, the oxidation of ethanol does not occur.
Also accept: Sulfuric acid supplies H+ ions needed for the redox reaction. Without it, potassium dichromate(VI) cannot oxidise ethanol.; The acid gives the solution the hydrogen ions required so the oxidising agent works.; H+ ions from sulfuric acid are essential for oxidation to occur.
Common mistakes: Saying only 'to make the solution acidic' without explanation; Not mentioning H+ ions or linking role to the redox reaction
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Marking points
M1 · 1 mark · States that the sulfuric acid provides H+ (hydrogen) ions needed for the reaction.
A1 · 1 mark · Explains that without H+ ions, potassium dichromate(VI) cannot oxidise ethanol (no reaction occurs).
Worked solution
Dilute sulfuric acid must be present because it provides hydrogen ions (H+) that allow the potassium dichromate(VI) to act as an oxidising agent. Without these H+ ions, the dichromate cannot oxidise ethanol, so no reaction happens.