1. 1
   Carbon monoxide (CO), carbon dioxide (CO₂) and methanol (CH₃OH) all contain carbon–oxygen bonds. In carbon monoxide the atoms are joined by a triple bond, in carbon dioxide each oxygen is joined to carbon by a double bond, and in methanol the carbon–oxygen bond is a single bond.

   (a)

   Which lists these compounds in order of increasing carbon–oxygen bond length?

   [1 mark]

   • ACH₃OH < CO₂ < CO
   • BCO₂ < CO < CH₃OH
   • CCO < CO₂ < CH₃OH
   • DCO = CO₂ = CH₃OH

   (b)

   Which of these molecules are polar?

   [1 mark]

   • ACO and CH₃OH only
   • BCO₂ and CH₃OH only
   • CCH₃OH only
   • DCO, CO₂ and CH₃OH

   (c)

   In the Lewis formula of CO, each atom has one lone pair and one of the three shared pairs is a coordination bond. Identify the atom that provides both electrons of the coordination bond and explain why this is needed for both atoms to obey the octet rule.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A food colouring is analysed by paper chromatography. The stationary phase is water held in the cellulose fibres of the paper, which is strongly polar; the mobile phase is a less polar mixture of ethanol and water. When the solvent front has moved 8.0 cm from the baseline, the colouring has separated into three spots, 1.6 cm, 5.6 cm and 7.2 cm from the baseline.

   (a)

   What is the Rf value of the spot 5.6 cm from the baseline?

   [1 mark]

   • A0.20
   • B1.43
   • C0.30
   • D0.70

   (b)

   Which component is most strongly attracted to the stationary phase relative to the mobile phase?

   [1 mark]

   • AThe component with Rf 0.70
   • BThe component with Rf 0.20
   • CThe component with Rf 0.90
   • DAll three are equally attracted

   (c)

   Suggest, in terms of intermolecular forces, why the component with Rf 0.90 travels furthest.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Three compounds have similar molar masses: propane, CH₃CH₂CH₃ (M = 44.11 g mol⁻¹, boiling point −42 °C); methoxymethane, CH₃OCH₃ (M = 46.08 g mol⁻¹, boiling point −24 °C); and ethanol, CH₃CH₂OH (M = 46.08 g mol⁻¹, boiling point 78 °C).

   (a)

   Deduce the strongest type of intermolecular force present in each of the three compounds.

   [3 marks]

   (b)

   Explain the order of boiling points of the three compounds.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Carbon and silicon are both in group 14. Diamond and graphite only change state above 3500 °C; diamond does not conduct electricity, while graphite conducts along its layers. Fullerene C₆₀ sublimes at about 600 °C, is a very poor electrical conductor and dissolves in methylbenzene. Silicon melts at 1414 °C, and silicon dioxide melts at 1710 °C. Carbon dioxide sublimes at −78 °C.

   (a)

   Explain the differences in electrical conductivity and volatility of diamond, graphite and fullerene C₆₀.

   [6 marks]

   (b)

   Explain the large difference in volatility between silicon dioxide and carbon dioxide, and why silicon melts at a lower temperature than diamond, even though silicon has the same type of structure.

   [6 marks]

   Total for question 4: 12 marks

End of questions