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CAIE A-Level Chemistry 17.1.4 Testing Carbonyls with 2,4-DNPH

Practise using 2,4-DNPH to detect aldehyde or ketone carbonyl groups from formation of a coloured precipitate.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • add 2,4-dinitrophenylhydrazine reagent to the unknown organic liquid or solution
  • record a yellow, orange or red precipitate as a positive result for an aldehyde or ketone C=O group
  • state that 2,4-DNPH confirms a carbonyl but does not by itself distinguish aldehyde from ketone

17.1.4—2,4-DNPH carbonyl test question 1

[Maximum number: 1]

4(CH3)3CCHO4\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO} is used in the synthesis of some antibiotics.

X, Y and Z are all isomers of (CH3)3CCHO\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO}.

A summary of some of the reactions and properties of X, Y and Z is shown in the table.

Table for Question 17.1.4—2,4-DNPH carbonyl test question 1 — CAIE A-Level Chemistry AS

X and Y each contains a carbonyl group.

Complete the table with the expected observations for the reactions of X and Y with 2,4-DNPH.

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