Testing for aldehydes and ketones

Question 1

Fehling solution is to test for a…

Answer 1

Aldehydes

Fehling’s solution can ONLY oxidise an ALDEHYDE but not a ketone

Question 2

Fehling’s solution test

Answer 2

Fehling solution is blue and contains Cu2+ ions

1) Add warm aldehyde to Fehling’s solution
colour change- BLUE solution to BRICK RED precipitate

2) Ketones remain blue

Question 3

Tollen’s reagent is to test for adehydes

Heres how to make it

Answer 3

1) Add a few drops of NaOH to silver nitrate solution- forming a pale brown precipitate
2) Add a few drops of dilute ammonia until the precipitate dissolves

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Question 4

Actual tollens reagent test..

Answer 4

Add tollens to warm aldehyde

• Aldehyde: silver mirror is produced, as tollens is reduced to silver which coats the inside of the flask
• Ketones: No silver mirror formed

ues water bath
don’t use bunsen burner as aldehydes and ketones are flammable