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Leaving Cert Physics & Chemistry: Alcohols, aldehydes & ketones

How often Alcohols, aldehydes & ketones comes up on the Physics & Chemistry papers, every year it was asked, and questions to try.

HL Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

OL Asked on 7 of the last 9 Ordinary Level papers, most recently in 2025. most years

Alcohols, aldehydes & ketones, Higher Level(6 marks)

Quick ones on Alcohols, aldehydes & ketones.

(a)Functional group of the alcohols?
  1. Carbonyl, C=O
  2. Hydroxyl, –OH
  3. Carboxyl, –COOH
(b)What is seen in a positive Fehling's test for an aldehyde?
  1. Colourless solution gives a milky white precipitate
  2. Purple solution turns colourless on heating
  3. Blue solution gives a red-brick precipitate
(c)Controlled (partial) oxidation of ethanol gives…
  1. Ethanal
  2. Methanol
  3. Ethene
Show the answers

(a) Hydroxyl, –OH

(b) Blue solution gives a red-brick precipitate

(c) Ethanal

Your turn: Higher Level questions on Alcohols, aldehydes & ketones.

Higher Level

Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q7(p), Q11
2024Q11
2023Q7(q), Q11
2022Q7(o), Q7(p), Q7(r), Q11
2021Q7(q), Q11
2019Q11
2018Q7(n), Q11
2017Q7(n), Q11
2016Q7(o), Q11

Links open the State Examinations Commission’s paper for that year.

More Alcohols, aldehydes & ketones questions

Alcohols, aldehydes & ketones, 2 marks

Name of CH3OH?

  1. Methanal
  2. Methane
  3. Methanol
Show the answer

Methanol

One carbon (meth-) with an –OH group (-ol). Methanal is HCHO, an aldehyde; methane is CH4.

Alcohols, aldehydes & ketones, 3 marks

Methanol (Mr 32) boils at 65 °C; ethane (Mr 30) boils at −89 °C. Why the big difference?

  1. Ethane molecules are much larger than methanol
  2. Hydrogen bonding between methanol molecules
  3. Methanol is an ionic compound with strong bonds
Show the answer

Hydrogen bonding between methanol molecules

Methanol's –OH groups form hydrogen bonds between molecules, which need extra energy to break. Ethane is non-polar, with only weak van der Waals forces.

Alcohols, aldehydes & ketones, 2 marks

Name of HCHO?

  1. Methanal
  2. Methanol
  3. Methanoic acid
Show the answer

Methanal

One carbon with the aldehyde group –CHO: methanal. Methanol has –OH; methanoic acid is HCOOH.

Ordinary Level

Asked on 7 of the last 9 Ordinary Level papers, most recently in 2025. most years

Every paper, year by year

YearWhere it came up
2025Q7(q), Q7(r)
2024Q7(q)
2023Q7(o), Q7(q), Q7(r)
2022Q7(o), Q7(p), Q7(q)
2021Q7(q)
2019Not asked
2018Q7(n), Q11
2017Q7(o)
2016Not asked

Links open the State Examinations Commission’s paper for that year.

More Alcohols, aldehydes & ketones questions

Alcohols, aldehydes & ketones, 2 marks

The functional group of an alcohol is?

  1. Carbonyl (C=O)
  2. Carboxyl (-COOH)
  3. Hydroxyl (-OH)
Show the answer

Hydroxyl (-OH)

Ethanol, C2H5OH, is the best-known alcohol. Aldehydes and ketones have the carbonyl group; carboxylic acids have the carboxyl group.

Alcohols, aldehydes & ketones, 3 marks

Gentle oxidation of ethanol gives?

  1. Ethane
  2. Ethanal
  3. Ethene
Show the answer

Ethanal

An oxidising agent (such as acidified dichromate) turns ethanol into the aldehyde ethanal. Further oxidation gives ethanoic acid.

Alcohols, aldehydes & ketones, 2 marks

Fehling's solution is heated with an aldehyde. The colour changes from?

  1. Blue to a red-brick precipitate
  2. Red-brick to a blue solution
  3. Purple to a colourless solution
Show the answer

Blue to a red-brick precipitate

Aldehydes are oxidised and reduce the blue copper(II) to red-brick copper(I) oxide. Ketones give no change, which is how to tell them apart.

Other Physics & Chemistry topics

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