Chemistry 5070 · O Level · Simple molecules and covalent bonds

Simple molecules and covalent bonds — practice question

The diagrams below show part of the structures of carbon dioxide and calcium carbide. The carbon dioxide molecules are displayed as O=C=O. Calcium carbide is represented as a lattice of Ca$^{2+}$ ions and C$_2^{2-}$ ions.
(a)[3]

Explain, in terms of structure and bonding, why carbon dioxide has a low boiling point and calcium carbide has a high boiling point.

(b)[1]

Calcium carbide, CaC$_2$, reacts with water to produce ethyne, C$_2$H$_2$, and calcium hydroxide. Construct the equation for this reaction.

(c)[1]

Ethyne is an unsaturated hydrocarbon. State the meaning of the term hydrocarbon.

(d)[1]

Ethyne is part of the alkyne homologous series. The molecular formulae of the first four members of the alkyne homologous series are shown: C$_2$H$_2$ C$_3$H$_4$ C$_4$H$_6$ C$_5$H$_8$ Predict the formula for the fifth member of the alkyne homologous series.

(e(i))[1]

What type of chemical reaction takes place when ethyne reacts with hydrogen?

(e(ii))[1]

Predict the molecular formula of a product formed when ethyne reacts with hydrogen.

(f)[2]

When excess ethyne reacts with chlorine, 1,2-dichloroethene is formed. The structure of 1,2-dichloroethene is shown. Deduce the partial structure of the polymer of 1,2-dichloroethene. Show three repeat units.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: carbon dioxide is a (simple) molecule

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