RP6 - Testing for Alcohols, Aldehydes, Alkenes and Carboxylic Acids

Question 1

Test for alkenes

Answer 1

Add bromine water and shake. Alkenes decolourise in bromine water.

Question 2

Test for aldehyde and ketones (1)

Answer 2

Add Tollen’s reagent and heat gently.

In aldehydes : Silver mirror formed
In ketones : No reaction. Remains colourless

Question 3

Test for aldehydes and ketones (2)

Answer 3

Add Fehling’s solution and heat gently

In aldehydes : Colour change from blue to red
In ketones : No reaction. Remains blue

Question 4

Test for carboxylic acids

Answer 4

Add sodium carbonate.
It will fizz/effervescence and produces CO2.
Bubble the gas through limewater. Limewater turns cloudy if CO2 is present.

Question 5

Test for halogenoalkanes

Answer 5

Add aqueous silver nitrate and warm
AgI gives yellow precipitate
AgBr gives cream precipitate
AgCl gives white precipitate

Question 6

Why is iodoalkane the most reactive halogenoalkane

Answer 6

C-I bond is the weakest bond so easier to break and therefore faster reaction.

Question 7

Test for primary and secondary alcohol

Answer 7

Add acidified potassium dichromate (VI) solution.
Colour change from orange to green

Question 8

Test for acyl chloride

Answer 8

Add silver nitrate at room temperature
There are steamy white fumes of HCl and white precipitate of AgCl formed