Organic Analysis
Required Practical 6: Tests for Alkenes, Alcohols, Aldehydes,
Haloalkanes and Carboxylic Acids
Alkenes (cyclohexene, cyclohexane)
o Add a few drops of bromine water
Cyclohexene – bromine water changes from orange-brown to colourless
Cyclohexane – no visible change, bromine water remains orange-brown
Alcohols (ethanol, propan-2-ol, 2-methylpropan-2-ol)
o Add 5 drops of potassium dichromate (K 2Cr2O7) and 10 drops of dilute sulfuric acid to 10
drops of each alcohol, then warm the mixture in a water bath
Ethanol – turns from orange to green solution
Propan-2-ol – turns from orange to green solution
2-methylpropan-2-ol – No visible change, solutions stays orange
Aldehydes (ethanal, propanone)
o Tollen’s Test
Place 5cm3 of silver nitrate into a test tube
Add a few drops of NaOH to form a precipitate
Add dilute ammonia drop by drop until it just dissolves (shaking well needed)
Add 10 drops of ethanal/propanone
Place in a water bath for 5 minutes
Ethanal – silver mirror formed
Propanone – no visible change
o Fehling’s Test
Mix 2cm3 of Fehling’s A with an equal volume of Fehling’s B
Add 1cm3 of ethanal/propanone
Place in a water bath (boil gently)
Ethanal – blue solution to red precipitate
Propanone – no visible change
Haloaklanes (1-chlorobutane, 1-bromobutane, 1-iodobutane)
o Add 5 drops of each haloalkane into 1cm 3 of ethanol in separate tubes
o Add 5 drops of NaOH (hydrolysis) and 10 drops of nitric acid (removes unwanted anions)
o Place in a water bath
o Put a test tube of 5cm3 silver nitrate in the water bath
o After 10 minutes add 1cm3 of the silver nitrate to each tube
o Shake the contents
o Add dilute ammonia and see if the precipitate dissolves
o Repeat from the beginning but add concentrated ammonia
o 1-chlorobutane – white precipitate dissolves in dilute ammonia
o 1-bromobutane – cream precipitate dissolves in concentrated ammonia
o 1-iodobutane – yellow precipitate does not dissolve in dilute or concentrated ammonia
Required Practical 6: Tests for Alkenes, Alcohols, Aldehydes,
Haloalkanes and Carboxylic Acids
Alkenes (cyclohexene, cyclohexane)
o Add a few drops of bromine water
Cyclohexene – bromine water changes from orange-brown to colourless
Cyclohexane – no visible change, bromine water remains orange-brown
Alcohols (ethanol, propan-2-ol, 2-methylpropan-2-ol)
o Add 5 drops of potassium dichromate (K 2Cr2O7) and 10 drops of dilute sulfuric acid to 10
drops of each alcohol, then warm the mixture in a water bath
Ethanol – turns from orange to green solution
Propan-2-ol – turns from orange to green solution
2-methylpropan-2-ol – No visible change, solutions stays orange
Aldehydes (ethanal, propanone)
o Tollen’s Test
Place 5cm3 of silver nitrate into a test tube
Add a few drops of NaOH to form a precipitate
Add dilute ammonia drop by drop until it just dissolves (shaking well needed)
Add 10 drops of ethanal/propanone
Place in a water bath for 5 minutes
Ethanal – silver mirror formed
Propanone – no visible change
o Fehling’s Test
Mix 2cm3 of Fehling’s A with an equal volume of Fehling’s B
Add 1cm3 of ethanal/propanone
Place in a water bath (boil gently)
Ethanal – blue solution to red precipitate
Propanone – no visible change
Haloaklanes (1-chlorobutane, 1-bromobutane, 1-iodobutane)
o Add 5 drops of each haloalkane into 1cm 3 of ethanol in separate tubes
o Add 5 drops of NaOH (hydrolysis) and 10 drops of nitric acid (removes unwanted anions)
o Place in a water bath
o Put a test tube of 5cm3 silver nitrate in the water bath
o After 10 minutes add 1cm3 of the silver nitrate to each tube
o Shake the contents
o Add dilute ammonia and see if the precipitate dissolves
o Repeat from the beginning but add concentrated ammonia
o 1-chlorobutane – white precipitate dissolves in dilute ammonia
o 1-bromobutane – cream precipitate dissolves in concentrated ammonia
o 1-iodobutane – yellow precipitate does not dissolve in dilute or concentrated ammonia
