Question

5(c). A chemistry student was provided with four samples of organic compounds, A, B, C, and D. Samples A and B each decolourised bromine in tetrachloromethane but only sample B reacted with a solution of ammoniacal silver trioxonitrate(V) to give a white precipitate. Sample D reacted with sodium trioxocarbonate(IV) to liberate carbon(IV) oxide. When heat was applied to the mixture of samples C and D in a test tube and drops of concentrated tetraoxosulphate(VI) acid added, a product with a fruity odour was formed. (i) Name the family of organic compounds to which samples A, B, C, and D belong; (ii) State why samples A and B reacted with bromine in tetrachloromethane; (iii) State why sample B gave a white precipitate with the solution of ammoniacal silver trioxonitrate(V); (iv) Give the name of the reaction between samples C and D; (v) State the two roles of the concentrated tetraoxosulphate(VI) acid in the reaction in 5(a)(iv).

Accepted Answer

(i) A belongs to the alkene family; B belongs to the alkyne family; C belongs to the alkanol (alcohol) family; D belongs to the alkanoic acid (carboxylic acid) family.
(ii) A and B reacted with bromine in tetrachloromethane because they are unsaturated compounds (a saturated compound like an alkane would not react this way).
(iii) Sample B gave a white precipitate because it is a terminal alkyne (which reacts with ammoniacal silver trioxonitrate(V) to give a silver-alkynide precipitate).
(iv) The reaction between samples C and D (an alcohol and a carboxylic acid, forming a fruity-smelling product) is Esterification.
(v) In esterification, concentrated H₂SO₄ serves two roles: (1) as a catalyst; (2) as a dehydrating agent.

WAEC Chemistry 2014 Theory — Question 36

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