1. 1
   Pauling electronegativity values are: K 0.8, Ca 1.0, B 2.0, Sn 2.0, I 2.7, N 3.0, Cl 3.2 and O 3.4. In the bonding triangle the average electronegativity is plotted horizontally and the electronegativity difference vertically, with the ionic vertex at the top, the metallic vertex at the bottom left and the covalent vertex at the bottom right.

   (a)

   Which compound has the greatest covalent character?

   [1 mark]

   • AKI
   • BCaO
   • CBN
   • DSnCl₄

   (b)

   A substance has an average electronegativity of 1.2 and an electronegativity difference of 0.4. Which properties are predicted?

   [1 mark]

   • AHigh melting point, brittle and conducts only when molten
   • BLow melting point and does not conduct in any state
   • CConducts only when dissolved in water
   • DConducts electricity as a solid and is malleable

   (c)

   Determine the position of tin(IV) chloride, SnCl₄, in the bonding triangle and predict its physical state at room temperature and its electrical conductivity.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Nylon-6,6 is used for ropes and clothing. It is made by condensation polymerisation of hexane-1,6-diamine, H₂N(CH₂)₆NH₂, and hexanedioic acid, HOOC(CH₂)₄COOH. The repeating unit has the formula C₁₂H₂₂N₂O₂. Relative atomic masses: H 1.01, C 12.01, N 14.01, O 16.00.

   (a)

   Which small molecule is released each time a new link forms in nylon-6,6?

   [1 mark]

   • AHCl
   • BH₂O
   • CNH₃
   • DCO₂

   (b)

   Which is the repeating unit of nylon-6,6?

   [1 mark]

   • A–[NH(CH₂)₆NHCO(CH₂)₄CO]–
   • B–[NH₂(CH₂)₆NH₂CO(CH₂)₄CO]–
   • C–[NH(CH₂)₆NHCO(CH₂)₆CO]–
   • D–[NH(CH₂)₆NHCOO(CH₂)₄OCO]–

   (c)

   Calculate the mass of water, in g, released when 1.00 kg of nylon-6,6 is formed. Assume every repeating unit releases two water molecules.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   PET, used for drinks bottles, is a polyester made from benzene-1,4-dicarboxylic acid, HOOC–C₆H₄–COOH, and ethane-1,2-diol, HO–CH₂CH₂–OH. Kevlar, used in body armour, is a polyamide made from benzene-1,4-diamine, H₂N–C₆H₄–NH₂, and benzene-1,4-dicarbonyl dichloride, ClOC–C₆H₄–COCl; the chains are straight and lie parallel to one another. PET softens at about 80 °C and melts at about 260 °C. Kevlar does not melt and only decomposes above about 450 °C; its fibres are about five times stronger than steel of the same mass.

   (a)

   Deduce the repeating unit of PET and identify the small molecule released during its formation.

   [3 marks]

   (b)

   Explain why Kevlar is much stronger than PET and decomposes rather than melts.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A council is comparing two types of carrier bag. One is made from poly(ethene), an addition polymer made from ethene obtained from crude oil. The other is made from poly(lactic acid), PLA, a condensation polymer made from lactic acid, CH₃CH(OH)COOH, which is obtained by fermenting maize starch; each lactic acid molecule has both a hydroxyl group and a carboxyl group. Poly(ethene) bags last for hundreds of years in landfill. PLA bags break down within about three months in industrial composting plants at about 60 °C, where the ester linkages are hydrolysed, but can last for years in cold seawater or in landfill.

   (a)

   Compare the formation of poly(ethene) and PLA, including the repeating unit of each polymer.

   [6 marks]

   (b)

   Evaluate the claim that PLA bags are better for the environment than poly(ethene) bags, explaining the durability of each polymer in terms of its structure and bonding.

   [6 marks]

   Total for question 4: 12 marks

End of questions