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CAIE A-Level Chemistry AS 17.1.6 Iodoform Test for Ch3co Group Questions

Practise the CAIE 9701 alkaline iodine test for methyl carbonyls, identifying CH3CO– and predicting CHI3 and carboxylate products.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • locate CH3CO– in an aldehyde or ketone before predicting a positive alkaline-I2 test
  • state that a pale-yellow or yellow precipitate of CHI3 forms in a positive reaction
  • draw the second carbon-containing product as the correct RCO2− ion after cleavage

CAIE A-Level Chemistry AS 17.1.6 Iodoform Test for Ch3co Group Questions question 1

[Maximum number: 1]

4P⃗,Q4 \vec{P}, Q and R all have the molecular formula C3H6O\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}. They are all structural isomers of each other.
P and Q each contain an oxygen atom bonded directly to a carbon atom that is sp2\mathrm{sp}^{2} hybridised. R contains an oxygen atom bonded directly to a carbon atom that is sp3\mathrm{sp}^{3} hybridised.

P and Q(C3H6O)\mathbf{Q}\left(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}\right) both form an orange precipitate when reacted with 2,4-DNPH. Only Q produces a yellow precipitate when reacted with alkaline aqueous iodine.

Identify the yellow precipitate formed by the reaction of Q with alkaline aqueous iodine.

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