OCR A Jun 2017 Paper 1 Q17 (with explained solutions) |

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OCR A Jun 2017 Paper 1 Q17

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17 This question is about Group 2 and Group 17 (7). 10 (a) Barium chloride can be prepared from barium hydroxide in a neutralisation reaction. Write the equation for this reaction. State symbols are not required.[1] (b) The reactivity of the Group 2 elements MgBa increases down the group. Explain why.[3] (c) On gently heating, the compound KCl O3 reacts as shown in the equation. KCl (s) + 3KCl O4(s) 4KCl O3(s) This reaction is an example of disproportionation. (i) State what is meant by disproportionation and use oxidation numbers to show that disproportionation has taken place.[3] (ii) What is the systematic name for KCl O4?[1]<br />
(d) Two changes are described below. 11 For each change,write an equation, including state symbols,state and explain how the entropy changes. (i) The reaction of aqueous barium nitrate with aqueous sodium sulfate. Full equation with state symbolsExplanation of entropy change[2] (ii) The change that accompanies the standard enthalpy change of atomisation of iodine. Equation with state symbolsExplanation of entropy change[2]<br />

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H432/01 Mark Scheme June 2017 Answer Marks Ba(OH)2 + 2HClBaCl2 + 2H2OGuidance ALLOW multiples IGNORE state symbols (even if wrong) FULL ANNOTATIONS WITH TICKS, CROSSES, CON, etc MUST BE USED IGNORE more orbitals OR more sub-shells Alternative must refer to shells ALLOW Energy levels for shells ALLOW more electron repulsion between shells IGNORE just shielding (more/greater needed) IGNORE nuclear shielding IGNORE pull for attraction IGNORE electrons less tightly held IGNORE nuclear charge for nuclear attraction IGNORE easier to remove electron Energy is required ALLOW less energy to oxidise Question (a) 17 (b) Increasing size: Atomic radius increases OR more shells OR more (electron) shieldingAttraction Nuclear attraction decreases OR (outer) electron(s) experience less attractionIonisation energy Ionisation energy decreases OR less energy needed to remove electron(s) <br />
H432/01 Question (c) (i) Disproportionation: Answer Mark Scheme Marks oxidation and reduction of the same elementRedox: Cl is oxidised from +5 (in KClO3) to +7 (in KClO4)Cl is reduced from +5 (in KClO3) to 1 (in KCl)(ii) potassium chlorate(VII)(d) (i) Equation Ba(NO3)2(aq) + Na2SO4(aq)BaSO4(s) + 2NaNO3(aq)Entropy change and explanation entropy decreases OR entropy change negative AND (BaSO4) solid/ppt has less disorder/ more order/ fewer ways of arranging energy/ less freedom/ less random particles/dispersal of energyJune 2017 Guidance ALLOW chlorine OR Cl for same element IGNORE species for element ALLOW after number, e.g. 5+ IGNORE ionic charges, e.g. Cl5+ IGNORE 5 (signs required) IGNORE any reference to electron loss/gain (even if wrong) ALLOW one redox mark if oxidation numbers are correct but reduction/oxidation is incorrectly assigned Brackets required ALLOW multiples M2 is dependent on BaSO4(s) (even if formula is incorrecteg Ba(SO4)2(s)) seen as a product in the attempted equation as long as reactants are not solid. BaSO4 solid/ppt may be assumed from BaSO4(s) seen in the attempted equation.<br />
Mark Scheme June 2017 Marks Guidance DO NOT ALLOW I2(s)2I(g) DEPENDENT onI2(s)I(g) OR I2(s)2I(g) H432/01 Question (ii) Equation AnswerI2(s)I(g)state symbols required Entropy change and explanation entropy increases OR entropy change positive AND gas has more disorder/ less order/ more ways of arranging energy/ more freedom/ more random particles / more dispersal of energyTotal 12 10<br />

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