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OCR A AS Jun 2016 Paper 1 Q23
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![23 This question is about properties of the halogens and halide ions. 17 (a) Bromine can be extracted by bubbling chlorine gas through concentrated solutions containing bromide ions. (i) Write the electron configuration of a bromide ion, in terms of sub-shells.[1] (ii) Write an ionic equation for this reaction and state why this reaction takes place in terms of reactivity of the halogens.[2] (b) Chlorine is used in water treatment. State one benefit and one risk of chlorine in water treatment. BenefitRisk[1] (c) Precipitation reactions can be used to distinguish between halide ions. (i) State the reagent needed for these precipitation reactions.[1] (ii) How would the appearance of the precipitates allow you to distinguish between chloride, bromide and iodide ions? ChlorideBromideIodide[1]OCR 2016 Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_QP_-_Paper_1_OCR_Chemistry_A_AS-Level_23.jpg)
![H032/01 Mark Scheme June 2016 Question 23 (a) Answer (i) 1s22s22p63s23p63d104s24p6Look carefully at 1s22s22p63s23p6there may be a mistake (a) (ii) Cl2 + 2Br2Cl + Br2(b) Chlorine/Cl/Cl2 is more reactive/stronger oxidising agent OR reactivity decreases down groupBenefit AND risk required for mark Benefits: kills OR removes bacteria AND Risk: toxic/poisonous OR forms chlorinated hydrocarbons OR forms carcinogens/toxic compoundsMarks AO element AO1.1 Guidance ALLOW 3d after 4s2 or after 4p6, e.g. 1s22s22p63s23p64s23d104p6 ALLOW upper case D, etc and subscripts, e.g. 4S23D1 DO NOT ALLOW [Ar] as shorthand for 1s22s22p63s23p6 AO1.1 AO1.1 ALLOW multiples, e.g. Cl2 + BrCl + Br2 IGNORE state symbols ALLOW bromine is less reactive IGNORE explanation in terms of electronegativity AO1.1 ALLOW kills germs OR kills micro-organisms OR kills pathogens OR sterilises/disinfects OR makes water potable/ safe to drink OR purifies water IGNORE antiseptic, reduces risk of disease, cleans water ALLOW reduces risk of water-born diseases, e.g. cholera/typhoid/dysentery IGNORE harmful/dangerous IGNORE chlorine is carcinogenic/ dangerous for health/causes breathing problems 11<br />
H032/01 Mark Scheme June 2016 Answer Marks AO element AO1.1 AO1.1 Guidance ALLOW Ag+ IF name correct, IGNORE an incorrect formula IGNORE acidified/HNO3 All three required for the mark Question (c) (i) Silver nitrate OR AgNO3Chloride: white (precipitate) AND Bromide: cream (precipitate) AND iodide: yellow (precipitate)(c) (ii) Total 12<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_MS_-_Paper_1_OCR_Chemistry_A_AS-Level_23-0.jpg)
