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CIE Jun 2017 v3 Paper 4 Q1
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![Answer all the questions in the spaces provided. PMT (a) Describe and explain the variation in the solubilities of the hydroxides of the Group 2 elements.[4] The table lists the standard enthalpy changes of formation, ions. , for some compounds and aqueous species Ba2+(aq) OH(aq) CO2(g) BaCO3(s) H2O(l) / kJ mol1 538 230 394 1216 286 (b) (i) Reaction 1 occurs when CO2(g) is bubbled through an aqueous solution of Ba(OH)2. Use the data in the table to calculate the standard enthalpy change for reaction 1, 1. Ba(OH)2(aq) + CO2(g) BaCO3(s) + H2O(l) reaction 1UCLES 2017 9701/43/M/J/17 1 =kJ mol1 [2]<br />
PMT If CO2(g) is bubbled through an aqueous solution of Ba(OH)2 for a long time, the precipitated BaCO3(s) dissolves, as shown in reaction 2. BaCO3(s) + CO2(g) + H2O(l) Ba(HCO3)2(aq) reaction 2 The standard enthalpy change for reaction 2, 2, = 26 kJ mol1. (ii) Use this information and the data in the table to calculate the standard enthalpy change of formation of the HCO3 (aq) ion. HCO3 (aq) =kJ mol1 [2] (iii) The overall process is shown by reaction 3. Use your answer to (ii), and the data given in the table, to calculate the standard enthalpy change for reaction 3, 3. Ba(OH)2(aq) + 2CO2(g) Ba(HCO3)2(aq) reaction 3 3 =kJ mol1 [1] (iv) How would the value of Ca(OH)2(aq) as shown in reaction 4? Explain your answer. 3 compare with the value of 4 for the similar reaction with Ca(OH)2(aq) + 2CO2(g) Ca(HCO3)2(aq) reaction 4[2] (c) The standard entropy change for reaction 1 is 1. Suggest, with a reason, how the standard entropy change for reaction 3 might compare with 1.[2]UCLES 2017 9701/43/M/J/17 [Total: 13] [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2017_v3_QP_-_Paper_4_CIE_Chemistry_A-level_1-0.jpg)
![9701/43 Question 1(a) 1(b)(i) 1(b)(ii) 1(b)(iii) 1(b)(iv) Cambridge International AS/A LevelMark Scheme PUBLISHED Answer solubility increases down the group Hlatt and Hhyd both decrease or Hlatt and Hhyd both become less exothermic / more endothermic Hlatt decreases / changes more (than Hhyd as OH being smaller than M2+) Hsol becomes more exothermic / more negative / less endothermic / less positive Hr1(538 + 2x230 + 394) = (1216 + 286) Hr11392 = 1502 Hr1 = 110 let Hf(HCO3 2y538 = 121639428626 y = 692 Hr3 5382(230 + 394) = 5382(692) Hr3 = 136 Hr3 will be identical to Hr4, / unchanged (aq)) = y as the reaction is the same, or: 2OH(aq) + 2CO2(g) (cid:127)(cid:127) 2HCO3 metal ions stay in solution/metal ions are unchanged / are spectators (aq) orUCLES 2017 Page 2 of 12 PMT May/June 2017 Marks 1 1 1 1 1 1 1 1 1 1 1<br />
9701/43 Question 1(c) Question 2(a)(i) 2(a)(ii) 2(a)(iii) 2(b)(i) 2(b)(ii) 2(c)(i) Cambridge International AS/A LevelMark Scheme PUBLISHED Answer more gaseous moles are being consumed (in reaction 3) or more CO2 moles are being consumed (in reaction 3) S is therefore expected to be more negative/less positive for reaction 3. 16 electrons on each diagram HNC = 115125 AND NCO = 180 Answer cyanic acid, because its a stronger / higher bond enthalpy / triple / CN / more electrons involved bond [H+] = ([HNCO]Ka) = (0.11.2104) or 3.46103 pH = log [H+] = 2.5 (2.46) Na2CO3 + 2(NH2)2CO (cid:127)(cid:127) 2NaNCO + CO2 + 2NH3 + H2O (n(OH) at start = (20.130) / 1000 = 6103 mol) (n(OH) reacted = (0.120) / 1000 = 2103 mol) n(OH) remaining = (62)103 = 4103 mol, (in 50 cm3) so [OH]end = (41031000) / 50 = 0.08 mol dm3UCLES 2017 Page 3 of 12 PMT May/June 2017 Marks 1 1 13 Marks 1 + 1 Total: 1 1 1 1 1 1 1 1<br />](https://learnah.org/wp-content/uploads/2018/08/June_2017_v3_MS_-_Paper_4_CIE_Chemistry_A-level_1-0.jpg)
