Edexcel Jun 2017 (IAL) Paper 1 Q21 (with explained solutions) |

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Edexcel Jun 2017 (IAL) Paper 1 Q21

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21 (a) The table below shows some of the ionisation energies of magnesium. Ionisation energy / kJ mol1 First 738 Second Third Fourth Fifth 1451 10541 13629 (i) Complete the table by predicting a value for the third ionisation energy of magnesium. (1) (ii) Write the equation for the third ionisation of magnesium. Include state symbols. (2) (b) A version of the Born-Haber cycle for magnesium chloride is shown below. Mg2+(g) + 2Cl(g) (cid:507)H3 (cid:507)H4 Mg2+(g) + 2Cl(g) (cid:507)H2 Mg(g) + 2Cl(g) (cid:507)H1 Mg(s) + Cl2(g) (cid:507)H5 MgCl2(s) 14 *P48382A01424* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br />
(cid:3) (cid:3) A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D (i) Identify the enthalpy changes from the Born-Haber cycle by completing the table. (cid:507)H 1 is the sum of two enthalpy changes and you should give both. Enthalpy change Identity of enthalpy change (cid:507)H1 (cid:507)H3 (cid:507)H5 (ii) Use the data in (a) to calculate the value of (cid:507)H2. (cid:3) (cid:3) (cid:507)H2 = (iii) Use your answer to (ii) and the following data to calculate the lattice energy of magnesium chloride, (cid:507)H4. Enthalpy change Value of enthalpy change / kJ mol1 (3) (1) (2) (cid:507)H1 (cid:507)H3 (cid:507)H5 +391.1 697.6 641.3 A E R A S I H T N I E T I R W T O N O D *P48382A01524* 15 Turn over<br />
(c) A similar Born-Haber cycle can be drawn for calcium chloride. *(i) In the calcium chloride cycle, the corresponding value for (cid:507)H2 is less positive. Explain why this is so. (2)D O N O T W R I T E I N T H I S A R E A*(ii) Explain why the value for the lattice energy, (cid:507)H4, is less negative for calcium chloride than for magnesium chloride. (2)(Total for Question 21 = 13 marks) 16 *P48382A01624* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br />
A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D BLANK PAGE A E R A S I H T N I E T I R W T O N O D *P48382A01724* 17 Turn over<br />

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Acceptable Answers Reject Mark Answers between 7000 and 8500, including 7000 and 8500 (kJ mol-1) (1) Acceptable Answers Reject Mark (2) Mg2+(g)Mg3+(g) + e(-)((g)) ALLOW Mg2+(g) - e(-)((g))Mg3+(g) Gaseous states for both magnesium species (1) Rest of equation correct (1) Acceptable Answers Reject Mark (3) EA of Cl2 (Enthalpy change of) H1 Atomisation of Mg (1) and (2x) atomisation ofCl2 / Cl / chlorine / Cl2 ALLOW Hat for (enthalpy change of) atomisation OR Bond enthalpy Cl-Cl for Hat Ignore state symbols H3 (2x) (first) electron (1) affinity of Cl / chlorine (2x) EA of Cl ALLOW Electron affinity of 2 Cl H5 Formation (of MgCl2) (1) Hf (of MgCl2) Question Number 21a(i) Question Number 21a(ii) Question Number 21b(i)<br />
Question Number 21b(ii) (+)2189 (kJ mol-1) Acceptable Answers Question Number 21b(iii) H4 = Acceptable Answers Reject Mark -2189 (kJ mol-1) (1) Reject Mark (2) incorrect unit, but allow the minor slip eg kJ mol- -641.3 (391.1 + 2189697.6) (1) = - 2523.8/ -2524 (kJ mol-1) (1) Final answer without working scores 2 Correct value with + sign scores 1 TE on incorrect value in (b)(ii) for 2 marks: (b)(ii) = +1451, (b)(iii) = -1785.8 (b)(ii) = -2189, (b)(iii) = (+)1854.2 If no value has been calculated in (b)(ii), H4 = -334.8 - H2 This scores (1) Acceptable Answers Reject Mark (2) Ca ions larger Just Ca is larger (than Mg) The molecules are larger Ca atom has a larger radius (than Mg)/ has more electron shells (than Mg) / has (outer) electrons which are further from nucleus OR The (outer shell) electrons in Ca are more shielded (1) (Outer shell) electrons experience less attraction from the nucleus OR require less energy/ are easier to remove (1) ALLOW reverse argument IGNORE References to charge density Question Number *21c(i)<br />
Reject Mark (2) Question Number *21c(ii) MP1 Acceptable Answers Mg2+ has higher charge density / same charge but smaller (radius) than Ca2+/ distance between ions is smaller IGNORE Mg2+ has higher polarising power than Ca2+ (1) MP2 So attracts Cl- more strongly (in MgCl2)/ so more energy is released when bond forms (1) MP2 depends on MP1 ALLOW reverse argument Atomic radius attracts chlorine References to incorrect type of bond/force (Total for Question 21 = 13 marks)<br />
Acceptable Answers Reject Mark Difficult to measure energy supplied/ take measurements while heating (the sample)/ to decide when reaction is complete ALLOW Difficult to measure the temperature of a solid Difficult to measure heat supplied/ heat absorbed (1) Just because requires heating Because of heat losses Acceptable Answers Reject Mark To protect from or prevent (the acid/ reaction mixture) spraying/ spitting/ splashing out/ bubbling over/ spilling with reason eg due to excessive frothing / stirring IGNORE Reaction is vigorous (1) Just spilling Acceptable Answers Reject Mark Mol HCl = (100 x 1.25 / 1000) =1.25 x 10-1 / 0.125 (1) Mol NaHCO3 = (8.0/84) = 0.095238/ 0.0952 Ignore SF except 1 SF (1) (2) Question Number 22(a) Question Number 22b(i) Question Number 22b(ii)<br />

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