Ethanol can be oxidised by heating with potassium dichromate(VI) in dilute sulfuric acid
3 marks · Easy| Experiment | Potassium dichromate(VI) | Dilute sulfuric acid | Observed colour change |
|---|---|---|---|
| 1 | Yes | Yes | Orange to green |
| 2 | Yes | No | Orange, no change |
| 3 | No | Yes | Colourless, no change |
Using the data from the table, explain in terms of ions, the importance of dilute sulfuric acid for this experiment.
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Dilute sulfuric acid is important because it provides hydrogen ions (H+) required for potassium dichromate(VI) to oxidise ethanol. Without sulfuric acid, no green colour appears, as no oxidation occurs.
Must show: must refer to H+ ions and necessity for potassium dichromate(VI) function
Also accept: H+ ions are needed for potassium dichromate(VI) to act as an oxidising agent.; Without H+ ions (from sulfuric acid), potassium dichromate(VI) does not oxidise ethanol and no colour change to green is observed.
Common mistakes: Sulfuric acid is needed to provide water
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Marking points
M1 · 1 mark · Identifies that H+ ions are provided by dilute sulfuric acid.
M2 · 1 mark · Links presence of H+ ions to the ability of potassium dichromate(VI) to oxidise ethanol.
A1 · 1 mark · Concludes from the data that no colour change occurs without sulfuric acid (no green produced).
Worked solution
Dilute sulfuric acid provides hydrogen ions (H+) needed for potassium dichromate(VI) to oxidise ethanol.
From the data, when sulfuric acid is absent (Experiment 2), the solution remains orange, showing no oxidation occurs.
Therefore, H+ ions are essential for this redox reaction and the observed colour change.