OCR A AS Jun 2016 Paper 2 Q1 (with explained solutions) |

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OCR A AS Jun 2016 Paper 2 Q1

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Answer all the questions. 1 Group 2 elements are metals that react with oxygen and water. (a) Magnesium is oxidised when it burns in oxygen to form an ionic compound. (i) Write the electron configuration, in terms of sub-shells, of a magnesium atom.[1] (ii) Explain what happens when magnesium is oxidised in terms of electron transfer.[1] (b) The trend in the first and second ionisation energies of Group 2 elements can be linked to the increase in chemical reactivity down the group. The first and second ionisation energies of calcium and strontium are given in the table. Element Ca Sr First ionisation energy / kJ mol1 Second ionisation energy / kJ mol1 590 550 1145 1064 (i) Write an equation, including state symbols, to represent the second ionisation energy of strontium.[1] (ii) Explain why the first ionisation energy of strontium is less than the first ionisation energy of calcium.[3]OCR 2016<br />
(c) A student reacts a Group 2 metal, M, with water. M(s) + 2H2O(l) M(OH)2(aq) + H2(g) The student measures the volume of hydrogen gas produced. 0.162 g of the metal produces 97.0 cm3 of gas measured at room temperature and pressure. (i) Draw a labelled diagram of the apparatus that can be used to carry out this experiment. (ii) Identify the Group 2 metal, M. Show your working. [2] (d) The student plans to repeat the experiment using the same mass of a Group 2 metal from further down the group. Group 2 metal =[3] Predict whether the volume of hydrogen produced would be greater than, less than or the same as the volume in the first experiment. Explain your answer.[1]OCR 2016 Turn over<br />

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H032/02 Question 1 (a) (i) 1s22s22p63s2Answer (ii) (Mg) loses/transfers/donates two electronsMark Scheme Marks AO element AO1.1 AO1.1 (b) (i) Sr+(g)Sr2+(g) + eAO2.5 AO1.2 3 (ii) Atomic radius larger atomic radius OR more shellsEffect of nuclear charge/shielding Increased nuclear charge outweighed by increased distance/shielding OR more/increased shieldingNuclear attraction less nuclear attraction OR less attraction on electronsJune 2016 Guidance ALLOW upper case S and P, and subscripts, e.g. 2S23P6 ALLOW Mg loses the 3s electrons provided electronic configuration in (a)(i) is 3S ALLOW MgMg2+ + 2e IGNORE reference to oxidation numbers / states ALLOW Sr+(g)eSr2+(g) ALLOW e for electron (i.e. charge omitted) IGNORE states on the electron FULL ANNOTATIONS MUST BE USED ----------------------------------------------------------- ALLOW ORA: comparison needed for each mark. ALLOW more/higher energy levels ALLOW electrons further from nucleus ALLOW extra/new shell IGNORE more orbitals OR more sub-shells OR different shell ALLOW more electron repulsion from inner shells IGNORE responses with no comparison IGNORE nuclear charge/effective nuclear charge ALLOW less nuclear pull OR electrons held less tightly<br />
H032/02 Question (c) Answer Mark schemes Marks (i) Diagram of labelled reaction vessel for reactionLabelled (gas) syringe OR diagram of gas collection over water in a labelled measuring cylinder / inverted burette. AND closed system with a tube connecting reaction vessel to gas collection apparatus1 1 AO element AO3.32 June 2016 Guidance ALLOW (conical) flask, test-tube or boiling tube. DO NOT ALLOW volumetric flask, beaker, measuring cylinder DO NOT ALLOW delivery tube below reacting solution ALLOW any of these diagrams. ALLOW a single line for the tube IGNORE Sealed end of delivery tube DO NOT ALLOW measuring tube<br />
H032/02 Mark schemes June 2016 Marks AO element AO2.8 Question Answer (ii) FIRST CHECK CALCULATED VALUE FOR MOLAR / ATOMIC MASS OF CALCIUM IF answer = 40.1 OR 40.08 is seen anywhere award first two marks n(H2) OR n(Group 2 metal) = 97.0 24 000 = 4.04103 (mol)molar mass/atomic mass of Group 2 metal = 0.162 0.00404 = 40.1 (g mol1)Group 2 metal: calcium/Ca(d) Less (volume/products) AND Smaller amount/fewer moles/fewer atoms of the metal OR element reacting Total 12 Guidance DO NOT ALLOW pV = nRT for the calculation of the amount in moles for marking point 1. ALLOW 3 SF up to calculator value correctly rounded (0.004041666) ALLOW 3 SF up to calculator value correctly rounded (40.08247423) ALLOW ECF from incorrectly calculated amount in moles DO NOT ALLOW Calcium if no working ALLOW ECF as element in Group 2 closest to the value calculated IGNORE higher relative atomic mass/molar mass ALLOW a calculation showing that moles and volume are less n(H2) = 0.162/87.6 = 0.0018493156 Volume = 0.001849315624000 = 44(.4) cm3 AO2.8 AO3.2 AO3.2<br />

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