6   3 This question is about elements in Group 7. (a) Group 7 elements react with many metals. (i) What happens to the atoms of a metal and the Group 7 element when they react together? (1) A B C D (ii) Which is not true when calcium reacts with bromine? (1) A bromine reacts less vigorously than chlorine B during the reaction bromine oxidises the calcium C the percentage by mass of calcium in the product is 33 % D the product gives a brick‑red flame test (iii) The equation for the reaction between aluminium and bromine is shown. 2Al + 3Br2 → Al2Br6 The compound is a dimer made up of two covalently bonded monomers joined by dative covalent bonds. Complete the dot‑and‑cross diagram, showing outer shell electrons only, of this dimer. Use • for bromine electrons and × for aluminium electrons. (2) Br Al Br Br Br Br Br Al Metal Group 7 element gains electrons to form a positive ion loses electrons to form a negative ion increases in oxidation number gains electrons to form a negative ion loses electrons to form a negative ion decreases in oxidation number loses electrons to form a positive ion increases in oxidation number Turn over 7   (iv) Platinum metal reacts with fluorine to give a compound of platinum with an oxidation number of +6. Give the formula of this compound of platinum. (1) .................................................................................................................................................................................................................................................................................... (v) Chromium reacts with iodine. The only product contains 12.0 % chromium by mass. Calculate the empirical formula of the chromium iodide formed. You must show your working. (2) (b) Chlorine, bromine and iodine are three of the Group 7 elements. The bond length and bond enthalpies in molecules of these elements are shown in the table. Bond Bond length / nm Bond enthalpy / kJ mol–1 Cl Cl 0.199 243.4 Br Br 0.228 192.9 I I 0.267 151.2 (i) Explain how the trend in bond length relates to the trend in bond strength on descending the group. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 8   (ii) The relative reactivity of chlorine and iodine can be demonstrated using the reaction between one of these elements and the potassium salt of the other halogen. Describe an experiment to show how this is deduced and give the expected observation for the reaction that occurs. Include an ionic equation for this reaction. State symbols are not required. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 3 = 12 marks) Turn over 9   4 The reaction between magnesium and chlorine can be carried out using the apparatus shown. concentrated hydrochloric acid (11.5 mol dm–3) flask containing potassium manganate(VII) tube containing coil of magnesium ribbon hole The coil of magnesium ribbon is first heated strongly until it just melts. Chlorine gas is then produced by a chemical reaction in the conical flask. The chlorine gas is passed over the heated magnesium, resulting in the formation of magnesium chloride. (a) In order to melt the magnesium, it must be heated strongly. Explain why the structure of magnesium gives it a high melting temperature. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 10   (b) The equation for the reaction to produce chlorine is shown. 2KMnO4 + 8HCl → 3Cl2 + 2KCl + 2MnO2 + 4H2O The concentration of the hydrochloric acid is 11.5 mol dm–3. The equation for the reaction between the chlorine and the magnesium is shown. Mg + Cl2 → MgCl2 Calculate the minimum volume of concentrated hydrochloric acid, in cm3, required to produce 4.00 g of magnesium chloride, MgCl2. Give your answer to an appropriate number of significant figures. (4) Turn over 11   (c) Bottles of potassium manganate(VII), KMnO4 , have three hazard warning labels. One of these is shown. This hazard symbol means that potassium manganate(VII) is liable to (1) A burn easily in the presence of oxygen B explode C react dangerously with oxygen D react vigorously with reducing agents (Total for Question 4 = 7 marks)