Turn over 11 5 The halogens are elements in Group 7 of the Periodic Table. (a) Chlorine compounds have many uses, including water treatment. (i) Chlorine and phosphorus (P4) can react to form phosphorus(V) chloride. The structure of a molecule of phosphorus is P P P P Some mean bond enthalpy values are shown in the table. Bond Mean bond enthalpy / kJ mol–1 P P +198 Cl Cl +243 P Cl +326 Calculate the enthalpy change for the reaction between chlorine and phosphorus to form phosphorus(V) chloride. 10Cl2 + P4 → 4PCl5 (3) 12 (ii) Give a reason why bond enthalpy values are always positive. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (b) Sodium chlorate(I) is a bleaching agent. (i) Sodium chlorate(I) can be made by the reaction of chlorine with sodium hydroxide. Show, by using oxidation numbers, that this reaction is disproportionation. 2NaOH + Cl2 → NaClO + NaCl + H2O (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (ii) A different bleaching agent can be made by the reaction of chlorine with sodium hydroxide under different conditions. Balance this equation. ............NaOH + ............Cl2 → NaClO3 + ............NaCl + ............H2O (1) (iii) What conditions are required for the reaction in (b)(ii)? (1) A cold and dilute alkali B cold and concentrated alkali C hot alkali D excess chlorine Turn over 13 (c) The halogens can be identified by their colour in an organic solvent such as hexane or cyclohexane. Which sequence of colours is correct for chlorine, bromine and iodine dissolved in an organic solvent? (1) Chlorine Bromine Iodine A orange red‑brown black B pale green orange black C orange red‑brown purple D pale green orange purple (d) Halide ions can be identified by their reaction with silver nitrate. (i) Write the ionic equation for the reaction between aqueous solutions of sodium iodide and silver nitrate. Include state symbols. (2) (ii) A solution containing 0.010 mol of a halide ion was reacted with excess silver nitrate and produced 1.88 g of precipitate. Identify the halide ion. Justify your answer. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 5 = 13 marks)