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.

Q: What topic does this question test?

This question tests Hydrocarbons in A-Level Chemistry (syllabus code 9701). It is worth 16 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Chemistry Oct/Nov 2017 examination, Paper 4 Variant 2 (9701_w17_qp_42.pdf).

Question

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.

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