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OCR A Jun 2013 Paper 5 Q1
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![Answer all the questions. 1 BornHaber cycles can be used to determine lattice enthalpies of ionic compounds. (a) Define, in words, the term lattice enthalpy.[2] (b) The BornHaber cycle below can be used to determine the lattice enthalpy of calcium oxide. The cycle includes the values for the enthalpy changes of the steps labelled AG. (i) Complete the BornHaber cycle by adding the species present on the two dotted lines. Include state symbols.step G +798 kJ mol1 step E +1145 kJ mol1 step F 141 kJ mol1 Ca2+(g) + O(g) + e Ca+(g) + O(g) + e step D +590 kJ mol1 Ca(g) + O(g) step C +249 kJ mol1 Ca(g) + 1/2O2(g) step B +178 kJ mol1 Ca(s) + 1/2O2(g) step A 635 kJ mol1OCR 2013 lattice enthalpy CaO(s) [2]<br />
(ii) Name the enthalpy changes for the following steps in the BornHaber cycle. step Astep Cstep G[3] (iii) Calculate the lattice enthalpy of calcium oxide. (c) Describe and explain the factors that affect the values of lattice enthalpies. answer =kJ mol1 [2][3] [Total: 12]OCR 2013 Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_5_QP_JUN13_question_1-0.jpg)
![F325 Mark Scheme June 2013 Question 1 (a) Answer (The enthalpy change that accompanies) the formation of one mole of a(n ionic) compound (cid:57) from its gaseous ions (under standard conditions) (cid:57) Marks (b) (i) (ii) Ca2+(g) + O2(g)Ca2+(g) + O(g) + 2estep G step F (enthalpy change of) formation (of calcium oxide) (cid:57) (enthalpy change of) atomisation of oxygen (cid:57) Second electron affinity (of oxygen) (cid:57) Guidance IGNORE 'energy needed' OR energy required ALLOW as alternative for compound: lattice, crystal, substance, solid Note: 1st mark requires 1 mole 2nd mark requires gaseous ions IF candidate response has 1 mole of gaseous ions, award 2nd mark but NOT 1st mark Correct species AND state symbols required for both marks 2e required for left-hand response ALLOW e for e Mark each marking point independently calcium oxide not required for this mark DO NOT ALLOW lattice formation (confusion with LE) atomisation AND oxygen/O2/O2/O both required (atomisation of calcium is also in cycle) IGNORE oxygen or oxygen species, e.g. O DO NOT ALLOW calcium<br />
F325 Mark Scheme June 2013 Question 1 (b) Answer (iii) FIRST, CHECK THE ANSWER ON ANSWER LINE IF answer = 3454 (kJ mol1) award 2 marks -------------------------------------------------------------------- 635 = 178 + 249 + 590 + 1145 + (141) + 798 + HLE(CaO) OR HLE(CaO) = 635[178 + 249 + 590 + 1145 + (141) + 798] OR 6352819 (cid:57) = 3454 (cid:57) (kJ mol1) Marks Guidance IF there is an alternative answer, check to see if there is any ECF credit possible using working below. See list below for marking of answers from common errors ------------------------------------------------------------- 1st mark for expression linking HLE(CaO) with H values ALLOW LE for HLE ALLOW for 1 mark: 3736 (+)3454 (+)2184 wrong sign before 2819 2184 1858 Any other number:CHECK for ECF from 1st marking point Award 1 mark for one transcription error only and everything else correct: e.g. +187 instead of +178 IF any value has been omitted, award zero use of +141 instead of 141 all signs reversed wrong sign for 635 wrong sign for +798<br />
Mark Scheme June 2013 Answer Marks Guidance IGNORE atomic and atoms and molecules and assume that size and charge refers to ions IGNORE LE increases OR LE decreases IGNORE bond strength; strength of ionic bonds F325 Question 1 (c) IGNORE nuclear attraction OR proton attraction For first 2 marks, (cid:120) (cid:120) Property AND effect required (cid:120) (cid:120) (cid:120) First 2 marks Decrease in (ionic) size AND more negative LE OR more exothermic OR more attraction (cid:57) Increase in (ionic) charge OR charge density AND more negative LE OR more exothermic OR more attraction (cid:57) ----------------------------------------------------------------------------------- Link between LE and attraction Lattice enthalpy correctly linked to attraction between IONS at least once (cid:57) e.g. Greater attraction between ions gives more negative LE Total ANNOTATE WITH TICKS AND CROSSES, etc ORA throughout ALLOW pull for attraction IGNORE just greater force (could be repulsion) IGNORE responses in terms of packing IGNORE electron density IGNORE lower/higher LE ---------------------------------------------------------------- For 3rd marking point ONLY, IONS is essential; DO NOT ALLOW attraction between atoms or molecules DO NOT ALLOW nuclear attraction 12<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_5_QP_JUN13_answer_1-0.jpg)
