Testing For Organic Functional Groups

Question 1

Testing for the alkene

Answer 1

Add a few drops of bromine water to each chemical
Stopper and shake
Test tube in which the bromine water is decolourised contains cyclohexene
Chemical equation: C6H10 + Br2 = C6H10Br2

Question 2

Testing for carboxylic acid

Answer 2

Add a small spatula of sodium carbonate to the remaining chemicals
Test tube with effervescence contains ethanoic acid

Chemical equation: 2CH3COOH + Na2CO3 = 2CH3COONa + H2O + CO2

Question 3

Testing for the aldehyde

Answer 3

Make tollens reagent: Place 3cm3 silver nitrate solution into a test tube. Add a drop of sodium hydroxide solution. Add dilute ammonia solution drop by drop until the brown precipitate dissolves to form a colourless solution.
Divide the tollens reagent into five portions and add a few drops to each remaining test tube
Place the test tubes in a water bath at 50 degrees c
Test tube in which silver mirror forms is the propanal
Chemical equation: CH3CH2CHO + (O) = CH3CH2COOH and Ag+ + e- = Ag

Question 4

Testing for Haloalkanes

Answer 4

To a small quantity of each remaining chemical add 1cm3 silver nitrate solution and 1cm3 ethanol
Place test tubes in a water bath at 50
Test tubes in which precipitates form contain haloalkanes (cream and yellow)
To the 2 precipitates add concentrated ammonia solution. The tube in which the precipitate remained contains 1-iodobutane
Equations: Ch3CH2CH2CH2Br + H2O = CH3CH2CH2CH2OH + Br- + H+

Question 5

Testing for Alcohols

Answer 5

To a small quantity of each remaining chemical add 1cm3 of dilute sulphuric acid and a few drops of potassium dichromate solution
Place the test tubes in a water bath at 50
Test tube in which a colour change from orange to green occurs contains the primary alcohol. The test tube which remains orange contains the tertiary alcohol
Equation: CH3CH2CH2OH + (O) = CH3CH2CHO + H2O