PAGS

Question 1

test for alkenes

Answer 1

1. add 2cm3 of sample to test tube
2. add 2cm3 of bromine water to same test tube
3. shake test tube
   +. decolourise (orange to colourless)
   -. nothing

Question 2

test for haloalkanes

Answer 2

1. add 5 drops of sample to test tube
2. add 1cm3 of ethanol and 1cm3 of aqueous silver nitrate
3. place test tube in warm bath
4. observe preciptate/colour change
   cl = white + soluble in dilute NH3
   br = pale cream + soluble in conc NH3
   I = pale yellow + insoluble in conc NH3

Question 3

test for phenols

Answer 3

1. add 2cm3 of sample to test tube
2. add 1 small spatula of solid sodium hydroxide(or 2cm3 of sodium hydroxide solution)
   +. (acid - phenol)solid dissolves + colourless solution of sodium salt forms
   -. (not acidic)nothing
3. add 2cm3 of sample to test tube
4. add 1 small spatula of a solid carbonate or 2cm3 of a carbonate solution(sodium carbonate)
   +. (phenol/base)nothing
   -. (strong acid)effervescence

Question 4

test for carboxylic acids

Answer 4

1. add 2cm3 of sample to test tube
2. add small spatula of solid carbonate(or 2cm3 of a carbonate solution) e.g sodium carbonate
3. if solution fizzes, bubble the gas trough limewater in second test tube
   +. fizzing + CO2 gas turns limewater cloudy
   -. nothing

Question 5

test for carbonyls

Answer 5

1. dissolve 0.2g of 2,4-DNP in 1cm3 of sulfuric acid,2cm3 of water and 5cm3 of methanol
2. in a different test tube, add 5 drops of sample to 2cm3 of earlier solution from 1)
3. shake the test tube and observe colour change
   +. bright orange precipitate
   -. nothing

Question 6

test for aldehydes

Answer 6

1) put 2cm3 of 0.10 moldm-3 silver nitrate solution in a test tube
2) add 5 drops of 0.80 moldm-3 sodium hydroxide (forms light brown precipitate)
3) add drops of dilute ammonia solution until the brown precipitate completely dissolves
4) place test tube in hot water bath and add 10 drops of aldehyde/ketone and wait a few minutes
+. (aldehyde) formation of silver mirror
-. nothing

Question 7

test for primary/secondary alcohols

Answer 7

1) add 10 drops of the alcohol to 2cm3 of acidified potassium dichromate solution in a test tube
2) warm the mixture gently in hot water bath
3) observe colour change
+. orange dichromate(VI) ion Cr2O72- reduced to green chromium(III) ion Cr3+
1 = orange to green slowly(continuation will further oxide to carboxylic acid)
2 = orange to green slowly
3 = nothing

Question 8

separation of water soluble impurities

Answer 8

• if product is insoluble in water
  1) separating funnel + water
  2) funnel shaken + layer allowed to settle (organic layer less dense than aqeous layer(with water oluble imprities) so settles on top)
  3) open stopper + collect aqeous layer
  4) aqeous layer contains water so must be dried = cacl2/mgso4(drying agent) results in lumpy
  5) filter to remove solid drying agent