AQA Jun 2010 Paper 5 Q1

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section a answer all questions in the spaces provided do not write outside the box calcium fluoride occurs naturally as the mineral fluorite a very hard crystalline solid that is almost insoluble in water and is used as a gemstone tables and contain thermodynamic data table process ca s ca g ca g ca g e ca g ca g e f g f g f g e f g h kj mol table name of enthalpy change h kj mol enthalpy of lattice dissociation for calcium fluoride enthalpy of lattice dissociation for calcium chloride enthalpy of hydration for f ions enthalpy of hydration for cl ions enthalpy of hydration for ca ions a write an equation including state symbols for the process that occurs when the calcium fluoride lattice dissociates and for which the enthalpy change is equal to the lattice enthalpy mark wmp jun chem b i define the term standard enthalpy of formation do not write outside the box marks extra space b ii write an equation including state symbols for the process that has an enthalpy change equal to the standard enthalpy of formation of calcium fluoride mark b iii use data from the tables and to calculate the standard enthalpy of formation for calcium fluoride marks extra space question continues on the next page turn over wmp jun chem do not write outside the box c explain why the enthalpy of lattice dissociation for calcium fluoride is greater than that for calcium chloride marks d calcium chloride dissolves in water after a certain amount has dissolved a saturated solution is formed and the following equilibrium is established cacl s ca aq cl aq d i using data from table calculate the enthalpy change for this reaction marks d ii predict whether raising the temperature will increase decrease or have no effect on the amount of solid calcium chloride that can dissolve in a fixed mass of water explain your prediction if you have been unable to obtain an answer to part d i you may assume that the enthalpy change kj mol this is not the correct answer effect on amount of solid that can dissolve explanation marks wmp jun chem do not write outside the box e calcium fluoride crystals absorb ultra violet light some of the energy gained is given out as visible light the name of this process fluorescence comes from the name of the mineral fluorite use your knowledge of the equation e h to suggest what happens to the electrons in fluorite when ultra violet light is absorbed and when visible light is given out marks extra space turn over for the next question turn over wmp jun chem

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