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OCR A Jun 2016 Paper 1 Q2
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![This question is about halogens. (a) Solid chlorine and solid bromine have a similar structure. Name this structure.[1] (b) The intermolecular attractions in halogens are van der Waals forces. (i) Explain how van der Waals forces arise between halogen molecules.[3] (ii) The boiling points of chlorine and bromine are shown in the table. Halogen chlorine bromine Boiling point / C 34 59 Explain why bromine has a higher boiling point than chlorine.[2]OCR 2016<br />
(c) A student carries out test-tube experiments to prove the trend in reactivity of halogens. The student is provided with the following solutions:Chlorine gas and chlorine water are not available. bromine water aqueous iodine aqueous barium chloride aqueous magnesium bromide aqueous calcium iodide. The student carries out the minimum number of test-tube experiments using these solutions in the presence of cyclohexane (an organic solvent). State the solutions that need to be added together in order to prove the trend in reactivity of the halogens, using the minimum number of test-tube experiments. Describe the colour seen in the organic solvent at the end of each test-tube experiment.Write an ionic equation for one reaction that takes place.[5]OCR 2016 [Total: 11] Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JUN16_question_2-0.jpg)
![F321 Question 2 (a) Answer Simple molecular lattice (cid:51) Mark Scheme June 2016 (b) (i) M1 Creating the dipole mark Uneven distribution of electrons (cid:51) M2 Type of dipole mark This creates/causes an instantaneous dipole OR temporary dipole (cid:51) M3 Induction of a second dipole mark This causes an induced dipole on a neighbouring/adjacent molecule(s)/halogens (cid:51) Bromine has more electrons (than chlorine) (cid:51) M2 Relative force mark Bromine has stronger (OR more) van der Waals forces (between molecules) OR More energy is needed to break the van der Waals forces in bromine (cid:51) (ii) M1 Electron mark Mark Guidance ALLOW simple covalent OR simple molecular ie simple must be seen. DO NOT ALLOW simple covalent bonds IGNORE use of atoms for M1 and M2 ALLOW (random) movement of electrons ALLOW change in electron density ALLOW alternative expression for instantaneous dipole Eg transient dipole, oscillating dipole, momentary dipole, changing dipole DO NOT ALLOW the induction of an instantaneous or temporary dipole for M2 DO NOT ALLOW the idea of a permanent dipole OR formation of ions for M2 ALLOW resultant dipole on an adjacent molecule(s) IGNORE atoms for molecules IGNORE instantaneous/temporary for M3 ALLOW reverse argument throughout ALLOW chlorine has less electron shells IGNORE less shells IGNORE reference to chlorine has less shielding for M1 ALLOW vdW ALLOW intermolecular forces OR dispersion forces OR London Forces OR induced dipole-dipole forces for van der Waals forces ALLOW less for weaker DO NOT ALLOW implication that any other attraction is broken for M2 eg Covalent bonds<br />
F321 Question 2 (c) Mark Scheme June 2016 Mark Answer M1 Mixing of first pair of solutions Adding (aqueous) barium chloride to bromine (water) OR BaCl2 + Br2 M2 Mixing of second pair of solutions Adding (aqueous) calcium iodide to bromine (water) OR Cal2 + Br2 OR Adding aqueous magnesium bromide to aqueous iodine OR MgBr2 + I2 M3 Colours in cyclohexane Colour for M1 is orange OR yellow AND Colour for M2 is purple OR violet OR mauve OR pink OR lilac M4 Ionic equation mark Br2 + 2I --> I2 + 2Br M5 Use of M1 and one of M2 as only two experiments Guidance For M1 and M2 ALLOW any halide for the named halides in the question eg potassium chloride for barium chloride potassium bromide DO NOT ALLOW barium chlorine/BaCl calcium iodine/CaI magnesium bromine/MgBr as the halide DO NOT ALLOW bromide for bromine OR iodide for iodine M1 can be seen anywhere M2 could be awarded from a correct ionic equation in M4 M2 can be seen anywhere If both M2 tests and M1 are given, this will nullify M5 M3 is given for the correct resultant colour of pairs of solution given in M1 and M2. If both possible pairs of solutions in M2 are given, both colours must be correct. IGNORE colours of other combinations of solutions IGNORE colours in the aqueous layer if stated DO NOT ALLOW other colours for M1 and M2 (eg iodine is brown) M4 can be awarded anywhere M4 also scores M2 if not already awarded ALLOW multiples IGNORE state symbols IGNORE I2 + 2Br --> I2 + 2Br IGNORE Br2 + 2Cl --> Br2 + 2Cl DO NOT ALLOW other ionic equations DO NOT ALLOW if more than two experiment are attempted even if pointless eg barium chloride + calcium iodide Place the tick for M5 against the sub-total mark, [5], at the bottom right hand side of the answer space Total 11<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JUN16_answer_2-0.jpg)
