Testing for organic functional groups

Question 1

Testing for alkenes

Answer 1

• Halogens can be used to test for C=C
• Unknown compounds can be shaken with bromine water (orange)
• If C=C present, will turn colourless

Question 2

Testing for alcohols

Answer 2

• Add potassium dichromate to sample
• Shake and heat
• If primary or secondary alcohol, will change from orange to green
• If tertiary, will remain orange

Question 3

Testing for aldehydes (Fehling’s)

Answer 3

• When mixed with aldehyde, turns from blue to brick red
• Ketones will remain blue

Question 4

Testing for aldehydes (Tollens’)

Answer 4

• When warmed with an aldehyde, forms a silver mirror
• Ketones, there is no visible change

Question 5

Testing for carboxylic acids

Answer 5

• Add sodium carbonate
• If gas produced, bubble it through limewater
• If carboxylic acid present, turns cloudy