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Edexcel Jan 2013 Paper 1 Q18
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![(2) (3) 18 This question is about lithium iodide, an ionic salt. (a) Draw dot and cross diagrams for the lithium and iodide ions. Show all the electrons in the lithium ion but only outer shell electrons in the iodide ion. (b) On the Born-Haber cycle below, fill in the missing formulae (including state symbols) and the missing enthalpy change. Hlat[LiI(s)]+LiI(s) Em1[Li(g)] Eaff1[I(g)] Li(g)Hf[LiI(s)] Hat[Li(s)]+*P41212A01324* 13 Turn over<br />
(c) Calculate the electron affinity of iodine, Eaff1[I(g)], using the data below. Lattice energy for lithium iodide, Hlat Enthalpy change of atomization of lithium, Hat Enthalpy change of atomization of iodine, Hat First ionization energy of lithium, Em1 Enthalpy change of formation of lithium iodide, Hf H/kJ mol1 759 +159 +107 +520 270 (d) The experimental lattice energy for lithium iodide is 759 kJ mol1. The theoretical lattice energy is different from this value. Will the experimental lattice energy be more negative or less negative than the theoretical lattice energy? Justify your answer. (2) (3)14 *P41212A01424*<br />
(e) State and explain how electron affinity values change as you go down Group 7 from chlorine to iodine. (2)(Total for Question 18 = 12 marks) *P41212A01524* 15 Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/l_smalljpgJanuary_2013_QP_-_Unit_1_Edexcel_Chemistry_A-level_18-0.jpg)
![PMT Reject Mark Reject Mark Acceptable Answers xx [:Li]+ (1) xx l xx xx (1) Accept all or mixture of dots and crosses Check inner electrons present on lithium If no element symbols but fully correct with Li first give 1 max If no / incorrect charge(s) if the electrons are correct 1 max If arrow drawn from third / outer shell electron on lithium to join electrons in iodine / iodide with correct charges scores 1 max Brackets are not essential Acceptable Answers Li(s) and Li+(g) and I(g) (1) I2(s) and I(g) (1) (Hat )[I2(s)] (1) Notice the square brackets are essential for this mark If wrong state for iodine element ie if I2(g/l) and consistent (Hat)[I2(g/l)] allow third mark If I(s) given for element and (Hat) [I(s)] allow third mark If wrong state with monatomic iodine both the last two marks lost If Li+(g) + e appears ignore electron Question Number 18 (a) Question Number 18 (b)<br />
PMT Mark Acceptable Answers First mark for one of: 270 = + 159 + 107 + 520 + electron affinity759 Or Electron affinity = 270(159 + 520 + 107759) (1) OR Electron affinity = 270 - 159 - 520 - 107 + 759 (1) Second mark for: (Electron affinity =) 297 (kJ mol1) (1) 297 (kJ mol1) alone scores (2) NB providing method is recognisable with one transcription error eg 795 for 759 and the final answer is consistent 1 max NB (+) 297 (kJ mol1) 1 max Reject Wrong unit e.g. J Question Number 18 (c)<br />
PMT Mark Reject Greater / less Increase / decrease alone Mark Reject Greater / less / Increase / decrease alone Any indication of ionization/ removing an electron Acceptable Answers (Experimental lattice energy is) more negative / exothermic (1) OR Theoretical lattice energy is less negative / exothermic (1) OR Recognition that more energy released (1) Irrespective of first answer then, any two from: Due to a degree of covalency (1) Deviation from pure ionic model (in experimental value) OR The theoretical model is pure ionic bonding (1) Polarization / distortion of the iodide / negative ions (by the lithium ion). Can be shown by diagram (1) Iodine/ I / I2 ion is not acceptable but iodine / I anion is allowed Note I2 anion is not allowed Acceptable Answers Electron affinities become less negative / less exothermic / more positive (going down Group 7) (1) As (added) electron further from the nucleus OR More shielding / shielded (from the nucleus) (1) Second mark stands alone Ignore larger (ionic) radius / atom / ion / charge density Question Number 18 (d) Question Number 18 (e)<br />](https://learnah.org/wp-content/uploads/2018/08/January_2013_MS_-_Unit_1_Edexcel_Chemistry_A-level_18-0.jpg)
