6   4 This question is about nitrogen and some nitrogen compounds. (a) A study of one brand of crisps found that each packet contained 0.420 g of nitrogen gas at a pressure of 120 kPa and a temperature of 20 °C. (i) Calculate the volume of nitrogen gas, in cm3, in one packet of crisps. [R = 8.31 J mol–1 K–1] (4) (ii) Give a possible reason why nitrogen gas and not air is used in packets of crisps. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (b) Draw dot‑and‑cross diagrams for a molecule of nitrogen gas and for the nitride ion, N3–, in sodium nitride, Na3N. Use dots () for nitrogen electrons and crosses (X) for electrons from sodium. (2) Nitrogen molecule Nitride ion Turn over 7   (c) Ammonia accepts a proton to form an ammonium ion. NH3 + H+ → NH4 + Explain why the ammonia molecule and the ammonium ion have different shapes and different bond angles. 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(d) Butylamine, C4H9NH2 , reacts with ethanoyl chloride. 2C4H9NH2 + CH3COCl → C4H9NHCOCH3 + C4H9NH3 +Cl– Explain how this equation illustrates that butylamine acts as a nucleophile and as a base. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 4 = 15 marks)