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WAChemistryQuick questions
Unit 4: Organic Chemistry and Chemical Synthesis
Quick questions on Oxidation of alcohols: WACE Year 12 Chemistry
5short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What are the oxidising agents?Show answer
The usual reagent is acidified potassium dichromate ( in dilute sulfuric acid), which is orange and turns green as the chromium is reduced from (orange dichromate) to (green chromium(III)). Acidified potassium permanganate () can also be used; it is purple and turns colourless. The colour change is the visual evidence of oxidation.
What are primary alcohols?Show answer
A primary alcohol oxidises in two stages:
What are secondary alcohols?Show answer
A secondary alcohol oxidises to a ketone, which resists further oxidation because there is no hydrogen on the carbonyl carbon to remove. For example, propan-2-ol oxidises to propanone.
What are tertiary alcohols?Show answer
A tertiary alcohol is not oxidised by acidified dichromate or permanganate. The carbon carrying -OH has no hydrogen, so there is nothing to remove, and the oxidant colour does not change. This lack of reaction is itself diagnostic.
What are distinguishing aldehydes from ketones?Show answer
Because aldehydes can be oxidised further (to carboxylic acids) but ketones cannot, you can distinguish them with a mild oxidant. An aldehyde will reduce a mild oxidising agent, whereas a ketone will not react, which provides a chemical test to tell the two carbonyl families apart.
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