(a) The letters R,S,T represent an alkene, an alkene and a terminal alkyne respectively. Which of R, S and T typically undergo(es) the following reactions?
(i) Addition reaction;
(ii) Combustion;
(iii) Substitution reaction.
(b)(i) Name the process by which an alkanol can be converted to an alkene.
(ii) Write the name and structural formula of the third member cf the alkanol series.
(iii) State what would be obtained if a primary alkanol reacted with excess acidified KMnO(_4) solution.
(c)(i) Give one chemical test for alkanoic acids.
(ii) Write an equation to show how methanoic acid reacts with ethanol in the presence of mineral acids.
(iii) What is the role of mineral acid in the reaction in (c) ii?
(d) In an experiment, cassava was pressure-cooked to release starch granules, followed by treatment with malt for about 2 hours at 55°C. Yeast was then added and the mixture was left for 2 days at 27°C. An organic product J and a gas H were obtained.
(i) Identify H
(ii) State the class of carbohydrates to which starch belongs and explain what happened to the starch during treatment with malt.
(iii) Draw a labelled diagram of a suitable set-up for obtaining a sample of J from the reaction mixture.
Explanation
(a) If R, S and T respectively are an alkene, alkene and a terminal alkyne:
(i) S and T would undergo addition reaction.
(ii) k, S and T would undergo combustion.
(iii) R and T would undergo substitution.
(b)(i) An alkanol is converted into an alkene by dehydration.
(ii) The third member of the alkanol series is propanol or propan – 2 – ol.
(iii) A primary alkanol reacts with excess acit’ified
(c)(i) Chemical test for alkanoic acid: Add (saturated) NaHCO(^{3}) or Na(_2)CO(_3)(solution), effervescence or gas evolved indicating alkanoic acid.
(ii) The reaction of methanoic acid with ethanol in the presence of mineral acid.
Equation: HCOOH + CH(_3)CH(_2)OH —> HCOOC(_2)H(_5) + H(_2)O
(iii) Role of mineral acid in (ii) above, is catalysis or acts as catalyst
(d) Cassava was pressure-cooked, then malt was added at 55°C for 2 hours followed by yeast. After 2 days at 27`C an organic product J and gas H were obtained
(i) H was CO(_2).
(ii) Starch is polysaccharide / complex carbohydrate. During treatment with malt, it was hydrolysed by diastascgcmylase Diastase
in malt to sugar / maltose.
(C(_6)H(_{10})O(_5))n + nH(_2)O (_n)C(_12)H(_{22})O(_{11})