AQA Jun 2013 Paper 2 Q11 (with explained solutions) |

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AQA Jun 2013 Paper 2 Q11

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do not write outside the box a group metals and their compounds are used commercially in a variety of processes strontium is extracted from strontium oxide sro by heating a mixture of powdered strontium oxide and powdered aluminium consider these standard enthalpies of formation hf kj mol sro s al o s sro s al s sr s al o s use these data and the equation to calculate the standard enthalpy change for this extraction of strontium the use of powdered strontium oxide and powdered aluminium increases the surface area of the reactants suggest one reason why this increases the reaction rate suggest one major reason why this method of extracting strontium is expensive marks question continues on the next page turn over wmp jun chem b explain why calcium has a higher melting point than strontium do not write outside the box marks c magnesium is used in fireworks it reacts rapidly with oxygen burning with a bright white light magnesium reacts slowly with cold water write an equation for the reaction of magnesium with oxygen write an equation for the reaction of magnesium with cold water give a medical use for the magnesium compound formed in the reaction of magnesium with cold water marks end of questions copyright aqa and its licensors all rights reserved wmp jun chem

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question a mark scheme general certificate of education a level chemistry unit chemistry in action june mark comments correct answer to the calculation gains all of m m and m credit mark for kj mol for other incorrect or incomplete answers proceed as follows check for an arithmetic error ae which is either a transposition error or an incorrect multiplication this would score marks m and m if no ae check for a correct method this requires either a correct cycle with sr and al or a clear statement of m which could be in words and scores only m ignore dividing final answer by penalise m for reference to molecules marking guidance m could be scored by a correct mathematical expression m h hf products hf reactants or a correct cycle of balanced equations m this also scores m m kj mol award mark only for m using powders any one from to increase collision frequency collisions in a given time rate of collisions to increase the surface contact contact between the solids contact between exposed particles m major reason for expense of extraction any one from aluminium is extracted by electrolysis or aluminium extraction uses large amounts of electricity reaction process it the mixture requires heat it is endothermic mark scheme general certificate of education a level chemistry unit chemistry in action june b calcium has a higher melting point than strontium because correct reference to size of cations proximity of electrons m for ca delocalised electrons closer to cations positive ions atoms nucleus or cations positive ions atoms are smaller or cation positive ion atom or it has fewer electron shells levels relative strength of metallic bonding m ca has stronger attraction between the cations positive ions atoms nucleus and the delocalised electrons or stronger metallic bonding assume argument refers to ca but credit converse argument for sr ignore general group statements penalise m if either of ca or sr is said to have more or less delocalised electrons or the same nuclear charge ignore reference to shielding ce for reference to molecules or van der waals forces or intermolecular forces or covalent bonds c m mg o mgo m mg h o mg oh h m magnesium hydroxide is used as an antacid relieve indigestion heartburn neutralise stomach acidity laxative credit multiples of the equations not simply milk of magnesia in m

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Topics to revise

AQA > Inorganic chemistry > Periodicity AS >

1 Periodicity

AQA > Inorganic chemistry > Group 2 AS >

3 Using Magnesium to extract Titanium

AQA > Inorganic chemistry > Group 2 AS >

2 Reactions with water and oxygen

AQA > Physical chemistry > Thermodynamics >

5 Gibb’s Free Energy

AQA > Physical chemistry > Equilibrium AS >

1 Dynamic equilibrium and factors affecting equilibrium

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