Calcium carbide, CaC2, reacts readily with water, forming ethyne, C₂H₂, and a sparingly soluble white ionic compound. (a)(i) Write an equation for this reaction. (a)(ii) Draw a 'dot-and-cross' diagram for the carbide ion, C22-. Show outer electrons only. Ethyne is the simplest member of the alkyne homologous series. H—C≡C—H ethyne Propyne, C3H4, and butyne, C₄H₁, are the next two members of the series.

1. (a)(i)Write an equation for this reaction.[1]
2. (a)(ii)Draw a 'dot-and-cross' diagram for the carbide ion, C22-. Show outer electrons only.[1]
3. (b)Deduce the general formula for the alkynes.[1]
4. (c)(i)Suggest why this polymer conducts electricity.[1]
5. (c)(ii)State the empirical formula of poly(acetylene).[1]
6. (c)(iii)By reference to a physical or chemical property, suggest one advantage of a conducting polymer when compared with metals.[1]
7. (d)(i)The first step of the mechanism of reaction 1 involves the alkyne anion reacting with the carbonyl compound. Complete the first step of the mechanism and draw the intermediate for this reaction. Include all relevant dipoles, charges and curly arrows.[3]
8. (d)(ii)Suggest the name of the mechanism in reaction 1.[1]
9. (d)(iii)An alkyne, Q, and a carbonyl compound, R, react together to form compound P as shown. [Figure 7.1] Use reaction 1 to suggest the structures of Q and R.[2]
10. (e)A series of twelve separate experiments is carried out as shown in the table. Complete the table by writing in each box a tick (✔) if a reaction occurs, or a cross (x) if no reaction occurs. CH₃CHO HCO₂H CH₃COCH₃ HO₂CCO₂H hot, acidified MnO₄(aq) alakaline I₂(aq) warm Tollens' reagent[4]

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