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Edexcel Jun 2017 Paper 4 Q18
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![A E R A S I H T N I E T I R W T O N O D SECTION C Answer ALL the questions. Write your answers in the spaces provided. 18 This question is about solutions, enthalpy changes and entropy changes. (a) (i) Draw a labelled Hess cycle and use it to calculate the enthalpy change of solution of barium chloride. Show all of your working. Hydration enthalpy of Ba2+ 1360 kJ mol1 Hydration enthalpy of Cl 364 kJ mol1 Lattice energy of BaCl2 2056 kJ mol1 (4) 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 *P48082A02328* 23 Turn over<br />
(ii) Explain how you would expect the value of the enthalpy change of hydration of calcium ions to compare with that of barium ions. (2)(b) Barium sulfate, BaSO4, dissolves to a very small extent in water and reaches equilibrium as shown in the equation. BaSO4(s) + aq (cid:85) Ba2+(aq) + SO4 2(aq) The equilibrium constant for this reaction is Kc = [Ba2+(aq)][SO4 2(aq)] (i) Suggest why the concentration of solid barium sulfate, [BaSO4(s)], is not included in the expression for Kc. (1)(ii) The value for Kc is 1.001010 mol2 dm6 at 298 K. Calculate the maximum mass, in g, of barium sulfate that will dissolve in 50.0 cm3 of water at 298 K. (3) 24 *P48082A02428* 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 />
A E R A S I H T N I E T I R W T O N O D (c) Hydrated barium hydroxide reacts with ammonium chloride as shown. Ba(OH)2.8H2O(s) + 2NH4Cl(s) (cid:108) 2NH3(g) + BaCl2(s) + 10H2O(l) (i) Use the Data Booklet to complete the table below. Ba(OH)2.8H2O(s) NH4Cl(s) 3345 314.4 NH3(g) 46.1 BaCl2(s) 427 94.6 192.3 (cid:168)H f / kJ mol1 S / J mol1 K1 (2) H2O(l) (ii) Use data from the table to calculate the standard enthalpy change, in kJ mol1, for this reaction. A E R A S I H T N Ba(OH)2.8H2O(s) + 2NH4Cl(s) (cid:108) 2NH3(g) + BaCl2(s) + 10H2O(l) (2) I E T I R W T O N O D (iii) Use data from the table to calculate the standard entropy change of the system, in J mol1 K1, for the same reaction. A E R A S I H T N Ba(OH)2.8H2O(s) + 2NH4Cl(s) (cid:108) 2NH3(g) + BaCl2(s) + 10H2O(l) (2) I E T I R W T O N O D *P48082A02528* 25 Turn over<br />
(iv) Use your answers to (c)(ii) and (c)(iii) to calculate (cid:168)Stotal for the reaction at 298 K. (3) D O N O T W R I T E I N T H I S A R E A *(v) It is possible that hydrated barium chloride, BaCl2.2H2O, forms instead of anhydrous barium chloride, BaCl2, in this reaction. Predict any effect on (cid:168)Ssystem if hydrated barium chloride forms instead of anhydrous barium chloride. Hence explain whether it is possible to predict the effect on the total entropy change of the reaction if hydrated barium chloride forms instead of anhydrous barium chloride. (3)TOTAL FOR SECTION C = 22 MARKS TOTAL FOR PAPER = 90 MARKS 26 *P48082A02628* 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 />](https://learnah.org/wp-content/uploads/2018/08/l_smalljpgJune_2017_QP_-_Unit_4_Edexcel_Chemistry_A-level_18-0-1.jpg)
![Acceptable Answers Reject Mark (4) BaCl2(aq) Incorrect unit Hsoln Hsoln Hhyd [Ba2+] + 2 x Hhyd [Cl ] / 1360 + (2 x 364) / 2088 Hhyd [Ba2+] + 2 x Hhyd [Cl ] / 1360 + (2 x 364) / 2088 Ba2+(g) + 2Cl(g) Hlatt /2056 BaCl2(s) (+aq)Ba2+(aq) + 2Cl(aq) / Ba2+(aq) 2Cl(aq) OR BaCl2(s) (+ aq)Ba2+(aq) + 2Cl(aq) / Ba2+(aq) 2Cl(aq) Hlatt /2056 Ba2+(g) + 2Cl(g) First mark All correct species including state symbols (1) Second mark Both arrows in correct directions ALLOW Arrows in opposite directions if labelling is correct for that direction (1) Third mark Arrows labelled with enthalpy change or values ALLOW LE for lattice energy and HE for hydration enthalpy ALLOW any unambiguous labels (1) Fourth mark Enthalpy change of solution = 1360 + (2 x 364)(2056) = 32 (kJ mol1) (1) ALLOW Other correct cycles ALLOW energy level diagram Hhyd [Ba2+] + 2 x Hhyd [Cl ] / 1360 + (2 x 364) / 2088 (kJ mol-1) Hsoln Ba2+(aq) + 2Cl(aq) Ba2+(g) + 2Cl(g) enthalpy Hlatt /2056 (kJ mol- 1) BaCl2(s) + aq Section C Question Number 18(a)(i)<br />
Acceptable Answers Question Number 18(a)(ii) Calcium (ions)/ Ca2+ have a smaller (ionic) Reject Mark (2) radius / are smaller (than barium ions/Ba2+) ALLOW higher charge density ALLOW calcium (ions) have a smaller atomic radius (1) So enthalpy of hydration is more exothermic / more negative (1) Question Number 18(b)(i) Acceptable Answers Reject Mark Its concentration / it is constant / does not change Solids do not have a concentration (1)<br />
Acceptable Answers Question Number 18(b)(ii) Correct answer with or without working Reject Mark (3) 2 (aq)] scores 3 marks [Ba2+(aq)] = [ SO4 So [Ba2+(aq)] = Ks = 1.00 x 1010 = 1.00 x 10 5 (mol dm3) (1) EITHER Conc BaSO4 = 1.00 x 10 5 x 233.4 = 2.334 x 103 (g dm3) (1) TE on [Ba2+(aq)] Mass BaSO4 in 50.0 cm3 = 2.334 x 103 x 50.0 1000 = 1.167 x 104 /1.17 x 104 /1.2 x 104 / 0.0001167 / 0.000117 / 0.00012(g) TE on conc BaSO4 in g dm3 (1) OR Mol BaSO4 in 50.0 cm3 = 1.00 x 10 5 x 50.0 1000 = 5.00 x 107 (1) TE on [Ba2+(aq)] Mass BaSO4 in 50.0 cm3 = 5.00 x 107 x 233.4 = 1.167 x 104 /1.17 x 104 /1.2 x 104 / 0.0001167 / 0.000117 / 0.00012(g) TE on mol BaSO4 in 50.0 cm3 (1) IGNORE SF except 1 SF Question Number 18(c)(i) Acceptable Answers Ho BaCl2(s) H2O(l) 858.6 285.8 /kJ mol-1 So /J mol-1 K-1 123.7 69.9 All 4 correct (2) Any 2 or 3 correct (1) Reject Mark (2)<br />
Reject Mark (2) Acceptable Answers Question Number 18(c)(ii) Correct answer with or without working Incorrect unit scores 2 marks [(2 x 46.1) + (858.6) + (10 x 285.8)][3345 + (2 x 314.4)] (1) = (+)165 (kJ mol-1) ALLOW Answer converted to J mol-1 TE from incorrect data in table in (a)(i) (1) ALLOW 1 mark for cycle wrong way round 165 (kJ mol-1) ALLOW 1 mark for using correct values but not multiplied by balancing numbers (+)2468.9 /(+)2469 (kJ mol-1) IGNORE SF except 1SF Acceptable Answers Reject Mark (2) Correct answer with or without working scores 2 marks [(2 x 192.3) + 123.7 + (10 x 69.9)][427 + (2 x 94.6)] (1) = (+)591.1 /(+)591 (J mol-1 K-1) ALLOW Answer converted to kJ mol-1 K-1 ALLOW TE from incorrect data in table in (a)(i) (1) ALLOW 1 mark for cycle wrong way round 591.1 / 591 (J mol-1 K-1) ALLOW 1 mark for using correct values but not multiplied by balancing numbers 135.7 / 136 (J mol-1 K-1) IGNORE SF except 1SF Question Number 18(c)(iii)<br />
Reject Mark (3) Acceptable Answers Question Number 18(c)(iv) Correct answer with or without working scores 3 marks Ssurr at 298 K = H/T =(165 x 1000) /298 (1) = 553.69 J mol1 K1 ALLOW answer as 0.55369 kJ mol1 K1 ALLOW M2 if M1 not used x 1000 (1) Stot = Ssurr + Ssys = 553.69 + 591.1 = (+)37.41 J mol1 K1 OR = 0.55369 + 0.5911 = (+)0.03741 kJ mol1 K1 ALLOW TE from (c)(iii) and Ssurr (1) IGNORE SF except 1 SF Acceptable Answers Reject Mark (3) (So for hydrated barium chloride will be greater than for anhydrous barium chloride as it is more complex) so this will increase Ssys (1) 8 water molecules are formed instead of 10 ALLOW fewer moles of products and this will decrease Ssys (1) as we do not know the extent of each change, we cannot predict the overall change on Stot OR No information about the effect on Ssurroundings / H ALLOW provided Ssurroundings does not change (1) TOTAL FOR SECTION C = 22 MARKS TOTAL FOR PAPER = 90 MARKS Question Number *18(c)(v)<br />](https://learnah.org/wp-content/uploads/2018/08/June_2017_MS_-_Unit_4_Edexcel_Chemistry_A-level_18-0-1.jpg)
