Ethanol can be oxidised by heating with potassium dichromate(VI) in dilute sulfuric acid
4 marks · NormalThe table shows the initial and final colours observed when ethanol is heated with potassium dichromate(VI) and dilute sulfuric acid.
| Test | Initial colour | Final colour |
|---|---|---|
| A | Orange | Green |
| B | Orange | Orange |
| C | Orange | Green |
Explain what has happened in each test. Suggest a reason why the outcome was different in test B.
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Tests A and C: Ethanol was oxidised (colour change orange to green). Test B: No oxidation (remains orange) – possibly ethanol was not added, or solution was not heated.
Also accept: Test B had no ethanol or was not heated.
Common mistakes: States test B did react, or ignores possibility ethanol or heat missing.
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Marking points
A1 · 1 mark · Correctly identifies orange to green change (A and C) as oxidation of ethanol occurs.
A2 · 1 mark · Correctly identifies no colour change (test B) as no reaction (no oxidation).
M1 · 1 mark · Suggests a sensible reason for no reaction in test B (e.g., ethanol not present, not heated, or acid missing).
A3 · 1 mark · Relates colour change to formation of Cr3+ ion.
Worked solution
| Test | Explanation |
|---|---|
| A and C | Colour changes from orange to green: ethanol has been oxidised, solution contains Cr3+ ions. |
| B | No colour change: no oxidation—not heated, no ethanol or acid absent. |