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

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AQA Jun 2013 Paper 5 Q2

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do not write outside the box a the enthalpy of hydration for the chloride ion is kj mol and that for the bromide ion is kj mol by describing the nature of the attractive forces involved explain why the value for the enthalpy of hydration for the chloride ion is more negative than that for the bromide ion marks b the enthalpy of hydration for the potassium ion is kj mol the lattice enthalpy of dissociation for potassium bromide is kj mol calculate the enthalpy of solution for potassium bromide marks wmp jun chem do not write outside the box c the enthalpy of solution for potassium chloride is kj mol c i explain why the free energy change for the dissolving of potassium chloride in water is negative even though the enthalpy change is positive marks extra space c ii a solution is formed when g of potassium chloride are dissolved in g of water the initial temperature of the water is k calculate the final temperature of the solution in your calculation assume that only the g of water changes in temperature and that the specific heat capacity of water is j k g marks turn over wmp jun chem

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mark scheme general certificate of education a level chemistry unit energetics redox and inorganic chemistry june marking guidance mark comments question a chloride ions are smaller than bromide ions so the force of attraction between chloride ions and water is stronger chloride ions attract the on h of water electron deficient h on water must state or imply ions allow chloride has greater charge density than bromide penalise chlorine ions once only max this can be implied from m and m but do not allow intermolecular forces allow attraction between ions and polar dipole water penalise h ions and mention of hydrogen bonding for m ignore any reference to electronegativity note if water not mentioned can score m only allow hsolution hl hhyd ignore units even if incorrect scores m and m scores scores m only transcription error b hsolution hl hhyd k ions hhyd br ions kj mol c i c ii mark scheme general certificate of education a level chemistry unit energetics redox and inorganic chemistry june the entropy change is positive entropy increases because mol solid mol aqueous ions no of particles increases therefore t s h amount of kcl mr mol heat absorbed kj heat absorbed mass sp ht t t t k t k s is negative loses m and m allow the aqueous ions are more disordered than the solid mention of atoms molecules loses m if moles of kcl not worked out can score m m only answer to m likely to be k process mark for m if calculation uses g not lose m only m m if not used can only score m m m m is for a correct t note that k scores m m m m if final temperature is negative m allow no units for final temp penalise wrong units

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