The correct answer is C because:

Acidified potassium dichromate (VI) is an orange oxidising agent.
- An oxidising agent is a species that oxidises another species and gets reduced itself.
- The reaction mixture turns green as the orange Cr₂O₇^2– ions (dichromate) are reduced to green Cr³⁺ ions.
- Only primary alcohols, secondary alcohols and aldehydes can be oxidised by acidified potassium dichromate (VI).

Hydroxyethanal contains a primary alcohol and aldehyde group.

Since the compound is heated under reflux until no further oxidation takes place, both the primary alcohol and the aldehyde are oxidised to carboxylic acid groups.
- Primary alcohol $\to$ aldehyde $\to$ carboxylic acid
- Aldehyde $\to$ carboxylic acid

The correct answer is therefore C.

A is incorrect as only the aldehyde group has been oxidised.

B is incorrect as this compound contains the incorrect number of carbon atoms in the carbon chain (there should be only 2 carbon atoms and not 3).

D is incorrect as the molecule is not fully oxidised; the aldehyde can undergo further oxidation to a carboxylic acid.

	1	At least one component of L is an alcohol.
	2	At least one component of L is a carbonyl compound.
	3	Only one of the components of L is a carbonyl compound.

	1	The last stage involves the formation of a hydrogen-oxygen bond.
	2	In the intermediate, the oxygen carries a negative charge.
	3	A new carbon-carbon bond is formed.

	1	Increasing the temperature.
	2	Performing the reacting under ultraviolet light.
	3	Adding a small quantity of aqueous sodium cyanide.

	1	Fehling’s reagent
	2	Aqueous bromine
	3	2,4-dinitrophenylhydrazine

	1	Butanal
	2	Pentan-3-one
	3	2-chlorobutane

	1	Black to yellow
	2	Orange to green
	3	Blue to red

	1	Warmed acidified K₂Cr₂O₇
	2	Fehling’s reagent
	3	NaBH₄

	1	X is a ketone
	2	X is butanone
	3	X is a carbonyl compound

Carbonyl Compounds (CIE AS Chemistry)

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