Oxidise methanoic acid to carbon dioxide and water
Recognise methanoic acid as a carboxylic acid that can be further oxidised to carbon dioxide and water by the listed oxidants.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 33. Focus on the named compounds, reagents and conditions in each outcome; apply the specified reaction type rather than extending it to unlisted cases. Written practice is self-checked
Before you begin
- Recall carboxylic acids, esters, phenols, alcohols, halogenoalkanes and electrophilic/nucleophilic reaction ideas from earlier topics.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What products form when methanoic acid is fully oxidised?
What you will learn
- Recall listed reagents for oxidising methanoic acid
- Identify CO₂ and H₂O as products
- Recognise methanoic acid as an exception among simple carboxylic acids
Methanoic acid can be oxidised further
Methanoic acid, HCOOH, is oxidised to CO₂ and H₂O. The syllabus lists Fehling’s reagent, Tollens’ reagent, acidified KMnO₄ or acidified K₂Cr₂O₇.
One balanced equation for complete oxidation is HCOOH + [O] → CO₂ + H₂O. The [O] represents the oxidising agent rather than a separate molecule supplied in that exact form.
Choose from the listed oxidants
When the question names an oxidant, use it and state the products. In a test question, Fehling’s or Tollens’ reagent may also produce a visible change as the reagent is reduced.
Do not generalise this to all carboxylic acids: the syllabus singles out methanoic acid as one that can be further oxidised.
Pause and explain
Which is a listed oxidant for methanoic acid?
Worked example
Name two syllabus reagents that oxidise methanoic acid and state the products.
Show the worked solution
- Choose any two from Fehling’s, Tollens’, acidified KMnO₄ or acidified K₂Cr₂O₇.
- Recognise the substrate is HCOOH.
- Name carbon dioxide and water.
Answer For example, acidified KMnO₄ or Tollens’ reagent oxidises methanoic acid to CO₂ and H₂O.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Complete the full-oxidation equation for methanoic acid using [O].
Give me a hint
Balance C, H and O atoms.
Compare my reasoning
- One carbon becomes one CO₂.
- Two hydrogen atoms become one H₂O.
- The remaining oxygen balance requires one [O].
HCOOH + [O] → CO₂ + H₂O.
Look for these in your work
- CO₂ formed
- H₂O formed
- Atoms balanced
Name four alternatives listed for oxidising methanoic acid.
Give me a hint
Include both aldehyde-style tests and strong acidified oxidants.
Compare my reasoning
- Fehling’s reagent
- Tollens’ reagent
- Acidified KMnO₄ or acidified K₂Cr₂O₇
Fehling’s, Tollens’, acidified KMnO₄ and acidified K₂Cr₂O₇ are the four listed options.
Look for these in your work
- Fehling’s
- Tollens’
- Both acidified oxidants
A student predicts ethanoic acid as the product when methanoic acid is oxidised. Correct the carbon accounting.
Give me a hint
Methanoic acid has one carbon atom.
Compare my reasoning
- The starting acid is HCOOH, with one carbon.
- Complete oxidation converts that carbon to CO₂.
- Water forms from the hydrogen and oxygen balance.
Methanoic acid is oxidised to CO₂ and H₂O; it does not gain a carbon to become ethanoic acid.
Look for these in your work
- Starting carbon count
- Oxidation product
- No carbon gain
Common mistakes
- Calling the product methanol
- Forgetting water
- Using alkaline KMnO₄ as if this were the methylbenzene oxidation
- Assuming every carboxylic acid is readily oxidised this way
What can you explain now?
What products form when methanoic acid is fully oxidised?
Compare with the explanation
CO₂ and H₂O
These are the stated products.
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Make it stick
Which oxidants can oxidise methanoic acid, and what are the products?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.