OCR A Jun 2010 Paper 5 Q1 (with explained solutions) |

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OCR A Jun 2010 Paper 5 Q1

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Answer all the questions. Lattice enthalpy can be used as a measure of ionic bond strength. Lattice enthalpies are determined indirectly using an enthalpy cycle called a BornHaber cycle. The table below shows the enthalpy changes that are needed to determine the lattice enthalpy of magnesium chloride, MgCl 2. letter enthalpy change 1st electron af nity of chlorine 1st ionisation energy of magnesium atomisation of chlorine formation of magnesium chloride atomisation of magnesium 2nd ionisation energy of magnesium lattice enthalpy of magnesium chloride energy / kJ mol1 349 +736 +150642 +76 +1450OCR 2010<br />
(a) On the cycle below, write the correct letter in each empty box. Mg2+(g) + 2Cl(g) + 2e Mg+(g) + 2Cl(g) + e Mg2+(g) + 2Cl (g) Mg(g) + 2Cl(g) Mg(g) + Cl2(g) Mg(s) + Cl2(g) (b) Use the BornHaber cycle to calculate the lattice enthalpy of magnesium chloride. MgCl2(s) [3] answer =kJ mol1 [2] (c) Magnesium chloride has stronger ionic bonds than sodium chloride. Explain why.[3]OCR 2010 [Total: 8] Turn over<br />

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F325 Question 1 Expected Answers Mark Scheme Marks F B E D G FIVE correct FOUR correct THREE correct (cid:57)(cid:57)(cid:57) (cid:57)(cid:57) (cid:57) Correct calculation June 2010 Additional Guidance ALLOW 1450 736 G 76 642 ALLOW for 1 mark: 2705 (2150 and 2349 not used for Cl) 2356 (2150 not used for Cl) 2855 (2349 not used for Cl) +2506 (wrong sign) DO NOT ALLOW any other answers ANNOTATIONS MUST BE USED ALLOW magnesium/Mg is 2+ but sodium/Na is 1+ DO NOT ALLOW Mg atom is 2+ but Na atom is 1+ ALLOW charge density here only ALLOW Mg OR magnesium is smaller DO NOT ALLOW Mg2+ has a smaller atomic radius ALLOW anion OR negative ion for Cl DO NOT ALLOW chlorine ions DO NOT ALLOW Mg has greater attraction ALLOW attracts with more force for greater attraction but DO NOT ALLOW greater force (could be repulsion) ALLOW reverse argument throughout in terms of Na+ 642(+76 + (2150) + 736 + 1450 + (2349) ) (cid:57) 6421864 =2506 (cid:57) (kJ mol1) Magnesium ion OR Mg2+ has greater charge (than sodium ion OR Na+) OR Mg2+ has greater charge density (cid:57) Magnesium ion OR Mg2+ is smaller (cid:57) Mg2+ has a stronger attraction (than Na+) to Cl ion OR Greater attraction between oppositely charged ions (cid:57) Total<br />

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