Organic Chemistry #13: Identifying Aldehydes and Ketones (Slides and Student Led Tasks)

LESSON OBJECTIVE: Describe chemical tests that can be used to test for, and distinguishing between, the carbonyls present in aldehydes and ketones

In this lesson we describe the 2,4-DNPH test to identify the carbonyl on an aldehyde or ketones and then investigates tests using Fehling’s and Tollens’ reagent to distinguish between the two. Finally we discuss the iodoform test to identify a methyl ketone group present. This is lesson thirteen in our organic chemistry series of Unit 18: Carbonyl compounds (from the Cambridge International AS Chemistry Curriculum (9701) 2019-2021 curriculum).

Learning Outcomes:
(taken from the Cambridge International AS and A Level Chemistry (9701) 2019-2021 curriculum)
18.1 Aldehydes and ketones
c) describe the use of 2,4-dinitrophenylhydrazine (2,4-DNPH) to detect the presence of carbonyl compounds

d) deduce the nature (aldehyde or ketone) of an unknown carbonyl compound from the results of simple tests (Fehling’s and Tollens’ reagents; ease of oxidation)

e) describe the reaction of CH3CO- compounds with alkaline aqueous iodine to give tri-iodomethane