# A student is given an unknown organic compound and is told it is either propan-1-ol or propanal. Describe how the student could use chemical tests to identify which compound is present. Include the reagents used, the observations for each test, and what each result tells the student.

> Eduqas A-Level Chemistry — 4.8 Organic synthesis and analysis · Describe · 5 marks

## Mark scheme (5 marks)

1. Add acidified potassium dichromate(VI) (and warm) / use Tollens' reagent / use Fehling's solution as a test reagent
2. State the observation with the aldehyde (propanal): e.g. acidified potassium dichromate turns from orange to green / Tollens' gives a silver mirror / Fehling's gives a brick-red precipitate
3. State the observation with the alcohol (propan-1-ol): acidified potassium dichromate still turns from orange to green (oxidised to an acid/aldehyde) OR Tollens' reagent gives no silver mirror / Fehling's solution stays blue
4. Correct interpretation: observation shows the compound is propanal (an aldehyde) because it is oxidised by Tollens'/Fehling's whereas propan-1-ol is not / aldehyde gives positive result with Tollens' or Fehling's that alcohol does not
5. Suggest a confirmatory or additional test to distinguish them — e.g. sodium metal / sodium carbonate: propan-1-ol produces bubbles of hydrogen (alcohols react with sodium); OR use of ester formation with ethanoic acid and acid catalyst confirming the presence of an –OH group

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