1. 1
   Boron trifluoride, BF₃, reacts with ammonia, NH₃, to form a single addition product, H₃NBF₃, in which boron is bonded to nitrogen. In aqueous solution, a cobalt(III) ion can bond to five ammonia molecules and one chloride ion to form a complex ion.

   (a)

   Which statement correctly describes the roles of the reactants when BF₃ reacts with NH₃?

   [1 mark]

   • ABF₃ is a Lewis base and NH₃ is a Lewis acid.
   • BBF₃ is a Lewis acid and NH₃ is a Lewis base.
   • CBF₃ is a Brønsted–Lowry acid and NH₃ is a Brønsted–Lowry base.
   • DBF₃ and NH₃ both act as nucleophiles.

   (b)

   What is the charge on the cobalt(III) complex ion described?

   [1 mark]

   • A2+
   • B3+
   • C4+
   • D1+

   (c)

   Explain, with reference to the outer electrons of boron and nitrogen, how the B–N bond in H₃NBF₃ forms and why it is described as a coordination bond.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Two organic preparations are carried out. In the first, bromoethane is heated with an excess of ammonia in ethanol in a sealed tube, forming ethylamine, CH₃CH₂NH₂. In the second, benzene is warmed with a mixture of concentrated nitric and sulfuric acids, which generates the nitronium ion, NO₂⁺, and nitrobenzene, C₆H₅NO₂, is formed.

   (a)

   Which species acts as the nucleophile in the preparation of ethylamine?

   [1 mark]

   • ACH₃CH₂Br
   • BBr⁻
   • CNH₃
   • DNO₂⁺

   (b)

   Which term describes the reaction between benzene and the nitronium ion?

   [1 mark]

   • AElectrophilic addition
   • BNucleophilic substitution
   • CNucleophilic addition
   • DElectrophilic substitution

   (c)

   Explain why benzene undergoes substitution rather than addition when it reacts with the nitronium ion.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Equal amounts of 1-chlorobutane, 1-bromobutane and 1-iodobutane were added to separate tubes of aqueous silver nitrate in ethanol at 50 °C. Water acts as the nucleophile, and the halide ion released forms a precipitate with Ag⁺. The times for a precipitate to appear were: 1-iodobutane 45 s, 1-bromobutane 6 minutes, 1-chlorobutane more than 60 minutes. When the experiment was repeated with 2-bromo-2-methylpropane, (CH₃)₃CBr, a precipitate appeared almost immediately. Bond enthalpies in kJ mol⁻¹: C–Cl 324, C–Br 285, C–I 228. Pauling electronegativities: C 2.6, Cl 3.2, Br 3.0, I 2.7.

   (a)

   Explain the order of reactivity of the three primary halogenoalkanes, and explain why bond polarity does not account for this order.

   [3 marks]

   (b)

   Explain why 2-bromo-2-methylpropane reacts much faster than 1-bromobutane, referring to the mechanism by which each compound reacts.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Ethene reacts with bromine at room temperature to form 1,2-dibromoethane. Propene reacts with hydrogen bromide to form mainly 2-bromopropane, with only a small amount of 1-bromopropane. When propene is hydrated with steam over a phosphoric(V) acid catalyst, the main organic product is propan-2-ol. A student claims that 2-bromopropane is the major product of the propene reaction because it is the more stable of the two possible products.

   (a)

   Describe and explain the mechanism of the reaction between ethene and bromine, stating the movement of each electron pair and including an overall equation.

   [6 marks]

   (b)

   Explain the major products formed when propene reacts with hydrogen bromide and with steam, and evaluate the student's claim.

   [6 marks]

   Total for question 4: 12 marks

End of questions