AQA Jan 2013 Paper 5 Q2 (with explained solutions) |

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AQA Jan 2013 Paper 5 Q2

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do not write outside the box this table contains some values of lattice dissociation enthalpies compound mgcl lattice dissociation enthalpy kj mol cacl mgo a write an equation including state symbols for the reaction that has an enthalpy change equal to the lattice dissociation enthalpy of magnesium chloride mark b explain why the lattice dissociation enthalpy of magnesium chloride is greater than that of calcium chloride marks extra space c explain why the lattice dissociation enthalpy of magnesium oxide is greater than that of magnesium chloride marks extra space wmp jan chem d when magnesium chloride dissolves in water the enthalpy of solution is kj mol the enthalpy of hydration of chloride ions is kj mol do not write outside the box calculate the enthalpy of hydration of magnesium ions marks extra space e energy is released when a magnesium ion is hydrated because magnesium ions attract water molecules explain why magnesium ions attract water molecules you may use a labelled diagram to illustrate your answer marks f suggest why a value for the enthalpy of solution of magnesium oxide is not found in any data books mark turn over wmp jan chem there are no questions printed on this page do not write on this page answer in the spaces provided wmp jan chem

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question a b mark scheme general certificate of education a level chemistry unit energetics redox and inorganic chemistry january marking guidance mark comments mgcl s mg g cl g the magnesium ion is smaller has a smaller radius greater charge density than the calcium ion attraction between ions to the chloride ion stronger the oxide ion has a greater charge charge density than the chloride ion so it attracts the magnesium ion more strongly hsolution hl hhyd mg ions hhyd cl ions hhyd mg ions hhyd mg ions kj mol if not ionic or if molecules imf metallic covalent bond pair electronegativity mentioned ce allow ionic bonds stronger do not allow any reference to polarisation or covalent character mark independently if not ionic or if molecules imf metallic covalent bond pair mentioned ce allow oxide ion smaller than chloride ion allow ionic bonds stronger mark independently allow correct cycle ignore units allow max for answer of or ce answer of ce c d mark scheme general certificate of education a level chemistry unit energetics redox and inorganic chemistry january e water is polar o on water has a delta negative charge mg ion ve ion charge attracts negative o on a water molecule f magnesium oxide reacts with water forms mg oh allow o not water has lone pairs can score on diagram allow mg attracts lone pair s m must be stated in words qol ignore mention of co ordinate bonds ce if o or water ionic or h bonding allow mgo does not dissolve in water sparingly soluble insoluble

Question 1 2 3 4 5 6 7 8

Topics to revise

AQA > Inorganic chemistry > Periodicity AS >

1 Periodicity

AQA > Physical chemistry > Thermodynamics >

5 Gibb’s Free Energy

AQA > Physical chemistry > Bonding AS >

6 Electronegativity and intermediate bonding

AQA > Inorganic chemistry > Transition metals >

6 Shape of complex ions

AQA > Physical chemistry > Atomic structure AS >

4 Electronic arrangement

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