Aldehydes and ketonesEdexcel International A Level Chemistry: Mind map

Exam questions on Aldehydes and ketones

1. A chemist compares three compounds of similar relative molecular mass: butane (Mr 58, boiling temperature −1 °C), propanal (Mr 58, boiling temperature 49 °C) and propan-1-ol (Mr 60, boiling temperature 97 °C).
   Explain why propanal has a higher boiling temperature than butane, even though their relative molecular masses are the same.2 marks
2. A technician has two unlabelled liquids, one is propanal and the other is propanone. She tests a sample of each with Tollens' reagent, with Fehling's solution and with acidified potassium dichromate(VI) solution, warming gently where necessary.
   Write an equation, using [O] to represent the oxidising agent, for the reaction of propanal with acidified potassium dichromate(VI), and state the colour change seen for propanal but not for propanone.2 marks
3. Compound X has the molecular formula C₄H₈O. It gives an orange precipitate with 2,4-dinitrophenylhydrazine solution. It gives no reaction when warmed with Tollens' reagent. It gives a pale yellow precipitate when warmed with iodine and sodium hydroxide solution.
   Deduce the structure and name of compound X, explaining each observation.3 marks