Ethanal - test for aldehydes

Question 1

Describe a chemical test to confirm that ethanal can be easily oxidised

Answer 1

-Add fehlings solution and heat gently
Blue cu2+ react and is reduced and forms a red precipitate
-Add Tollen’s solution which contains colourless At+
It reacts and is reduced and forms a silver mirror precipitate

Question 2

Suggest a weak oxidising reagent that could be used to distinguish between an aldehyde and a ketone

Answer 2

Fehlings reagent

Question 3

Why does propanone not react with Fehlings reagent

Answer 3

Propanone is not easily oxidised

Question 4

Describe the colour change observed when acidified potassium permanganate solution is added to ethanal and name the organic product formed

Answer 4

Purple colour of potassium permanganate changes to colourless
Organic product - ethanoic acid

Question 5

Describe the colour change observed when Fehlings solution is added to ethanal and name the organic product formed

Answer 5

Blue colour of solution disappears and red precipitate is formed.
Organic product - ethanoic acid

Question 6

What would you expect to observe when Fehlings reagent is added to some propanone in a test-tube? Explain your answer

Answer 6

No change observed since Fehling’s reagent does not oxidise ketones