AQA Jun 2016 Paper 5 Q3 (with explained solutions) |

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AQA Jun 2016 Paper 5 Q3

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do not write outside the box a this question is about magnesium chloride write the equation including state symbols for the process corresponding to the enthalpy of solution of magnesium chloride mark b use these data to calculate the standard enthalpy of solution of magnesium chloride enthalpy of lattice dissociation of mgcl enthalpy of hydration of magnesium ions enthalpy of hydration of chloride ions kj mol kj mol kj mol marks c solubility is the measure of how much of a substance can be dissolved in water to make a saturated solution a salt solution is saturated when an undissolved solid is in equilibrium with its aqueous ions use your answer to part b to deduce how the solubility of mgcl changes as the temperature is increased explain your answer marks wmp jun chem turn over for the next question do not write on this page answer in the spaces provided turn over wmp jun chem

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question a marking guidance mgcl s mg aq cl aq b c hsoln mgcl le hhydmg hhydcl hsoln mgcl x kj mol m solubility decreases as temp increases m the enthalpy of solution is exothermic reaction is exothermic backwards reaction is endothermic m according to le chatelier the equilibrium moves to absorb heat reduce temperature oppose the increase in temperature in the endothermic direction mark scheme a level chemistry chem june mark comments state symbols essential do not allow this equation with h o on the lhs ignore aq on the lhs allow h o written over the arrow allow equation written as an equilibrium allow correct equations to form mg h o ions m for expression in words or with correct numbers ignore units but penalise incorrect units if m is incorrect then ce if answer to b is a ve value allow m solubility increases as temp increases m enthalpy of solution is endothermic etc m according to le chatelier the equilibrium moves to absorb heat reduce the temperature oppose the increase in temperature in the endothermic direction of

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Topics to revise

AQA > Physical chemistry > Equilibrium AS >

1 Dynamic equilibrium and factors affecting equilibrium

AQA > Physical chemistry > Thermodynamics >

5 Gibb’s Free Energy

AQA > Physical chemistry > Atomic structure AS >

4 Electronic arrangement

AQA > Physical chemistry > Thermodynamics >

2 Born-Haber cycle

AQA > Inorganic chemistry > Periodicity AS >

1 Periodicity

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