Test for....

Question 1

Carboxylic acid

Answer 1

Sodium hudrogen carbonate.

Bubbles in solution / firzzing.

Question 2

Aldehydes

Answer 2

Reagent: Tollen’s reagent.

Conditions: Warmed.

Observation: Silver mirror formed.

Reason: Aldehyde acts as a reducing agent.

or

Reagent: Fehling’s reagent.

Observation: red-brown precipate of copper (I) oxide.

Reason: Copper (II) ions reduced to the copper (I) state, due to aldehyde acting as reducing agent.

Question 3

Oxidation of alcohol

Answer 3

Reagent: Acidified dichromate

Observation: Orange to green.

Question 4

Aldehyde and ketone

Answer 4

Reagent: 2,4-dinitrophenylhydrazine (2,4-DNP)

Mechanism: nucleophillic additions then elimination of small molecule (condenstation reaction)

Observation: orange-red precipate.

This is filtered and purified and the melting point is found and compared with values in a text box to find whether its an aldhyde or ketone.

Question 5

CH₃C-O group in ketones

Answer 5

Reagent: alkaline solution of iodine.

Observation: Yellow precipate (iodoform) formed.

Question 6

Phenol

Answer 6

Reagent: Iron(III) chloride solution.

Observation: purple solution.