Methanol (CH₃OH) is an alcohol that can be oxidised. Explain what happens when methanol undergoes oxidation, naming the product formed and describing how you could use acidified potassium dichromate(VI) solution to show that oxidation has taken place.

Edexcel A-Level Chemistry (9CH0) — 6.5 Alcohols and oxidation · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Methanol is the simplest alcohol. Like ethanol, it can undergo oxidation reactions. Acidified potassium dichromate(VI) solution is orange in colour.

Model answer (5 marks)

Oxidation of methanol involves the addition of oxygen to the alcohol, giving methanoic acid (formic acid). The reaction can be carried out with acidified potassium dichromate(VI) solution, which acts as the oxidising agent. During the reaction the orange dichromate(VI) ion is reduced to green chromium(III) ion. The change from orange to green therefore shows that the dichromate has been reduced, confirming that methanol has been oxidised to methanoic acid.

Examiner tips

  • Use the word "oxidation" to describe the gain of oxygen. Mention the specific product, methanoic acid. State that acidified K₂Cr₂O₇ is the oxidiser. Explain the orange‑to‑green colour change as evidence of reduction.
  • common_mistakes
  • :
  • Saying the product is ethanol or formaldehyde. Forgetting to mention the colour change. Using the wrong oxidising agent (e.g. sodium dichromate without acid).

Mark scheme (5 marks)

  1. Oxidation involves the gain of oxygen (by the methanol / alcohol)
  2. The product formed is methanoic acid (HCOOH)
  3. Acidified potassium dichromate(VI) solution is used as the oxidising agent
  4. The acidified potassium dichromate(VI) solution changes colour from orange to green
  5. This colour change shows that the dichromate(VI) has been reduced, confirming that oxidation of methanol has occurred

Key terms in this question

oxidation

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