(a)(i) What type of reaction is involved in each of the conversion processes indicated as I to V below? (ii) Name one isomer of glucose (iii) Explain why pa...

Answer Details

(a)(i) Type of reaction in each conversion (I to V)

(a)(ii) One isomer of glucose: fructose (galactose is also acceptable), each of formula C₆H₁₂O₆.

(a)(iii) Why palm wine becomes sour on prolonged exposure to air. Palm wine contains ethanol. On exposure to air, bacterial/atmospheric oxidation converts the ethanol to ethanoic (acetic) acid, and it is this acid that gives the drink its sour taste:

\[ CH_3CH_2OH + O_2 \rightarrow CH_3COOH + H_2O \]

(b)(i) Reagents and conditions for ethanoic acid to form an alkanoate

• An alkanol (e.g. ethanol).
• Concentrated H₂SO₄ (or dry HCl) as catalyst/dehydrating agent.
• Heat, about \(40^\circ\text{C}\) to \(110^\circ\text{C}\), or refluxing.

\[ CH_3COOH + C_2H_5OH \underset{\Delta}{\overset{conc.\,H_2SO_4}{\rightleftharpoons}} CH_3COOC_2H_5 + H_2O \]

(b)(ii) Two uses of alkanoates (esters)

• In the manufacture of perfumes, flavours and cosmetics.
• As solvents in the paint, pharmaceutical and food industries; also for making polyester fibres.

(c)(i) IUPAC name of the compound: but-2-yne, \( CH_3-C{\equiv}C-CH_3 \).

(c)(ii) Chemical test to distinguish methane from but-2-yne. Pass each gas in turn into bromine water (or acidified KMnO₄). But-2-yne, being unsaturated, rapidly decolourizes the reagent; methane, being saturated, gives no visible reaction and the colour remains.

(c)(iii) Combustion of ethene in excess oxygen

\[ C_2H_{4(g)} + 3O_{2(g)} \rightarrow 2CO_{2(g)} + 2H_2O_{(g)} \]