Question 1

Why are aldehydes readily oxidised?

Accepted Answer

An aldehyde contains a hydrogen atom directly attached to its carbonyl carbon. Oxidation removes this hydrogen and increases the oxidation state of the carbon, producing a carboxylic acid in acidic conditions or a carboxylate in an alkaline medium.

Question 2

Why do ketones resist mild oxidising agents?

Accepted Answer

The carbonyl carbon of a ketone is bonded to two carbon groups and has no hydrogen. Mild oxidising agents such as Tollens' reagent and Fehling solution therefore leave ordinary ketones unchanged.

Question 3

What changes are observed with the common aldehyde tests?

Accepted Answer

Tollens' reagent forms a metallic silver mirror, while Fehling's solution changes from blue to brick red because Cu2O precipitates. Acidified potassium dichromate changes from orange to green, and potassium permanganate becomes decolourised; brown MnO2 can form under suitable conditions.

Question 4

Why is the product written as RCOO- in some oxidations?

Accepted Answer

The form of the product depends on the reaction medium. In alkaline conditions, such as Tollens' or Fehling solution, the carboxylate ion RCOO- is obtained. In acidic conditions, the corresponding carboxylic acid RCOOH is represented.

Question 5

What happens when a ketone undergoes vigorous oxidation?

Accepted Answer

Vigorous oxidation can cleave the C-C bonds on either side of the carbonyl group. The carbon skeletons are converted into carboxylic-acid products, so a mixture of acids may be formed rather than one universal product.

Aldehyde & Ketone Oxidation 3D Lab

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