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Edexcel Jun 2010 Paper 4 Q19
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![Question Number 19 (a)(i) Question Number 19 (a)(ii) Question Number 19 (a)(iii) Acceptable Answers Reject Mark (Kp =) pCH3CO2H pCH3OH (x) pCO Partial pressure symbol can be shown in various ways, eg pp, pCO, (CO)p, etc ALLOW p in upper or lower case, round brackets IGNORE units [ ] State symbols given as (l) + in bottom line Acceptable Answers Reject Mark P CH3OH = 4.9 (atm) (1) P CO = 4.9 (atm) (1) 1 mark for recognition that pressures are equal IGNORE units Acceptable Answers Reject Mark Answers to other than 3 significant figures Kp = ((22.2)/(4.9)2) = 0.925 (1) atm1 (1) stand alone mark but must match expression used in (a)(iii) OR 9.25 x 104 Pa1 / 92.5 kPa1 (2) ALLOW TE from (a)(i) if inverted and/or (a)(ii)<br />
Question Number 19 (b)(i) Question Number 19 (b)(ii) Question Number 19 (b)(iii) Acceptable Answers Reject Mark CH3OH: 3.2 CO : 3.2 (1) for both values CH3CO2H: 46.8 (1) ALLOW TE for moles of ethanoic acid based on numbers of methanol and carbon monoxide used, as long as moles of methanol and carbon monoxide are equal and moles ethanoic acid + moles methanol = 50 Acceptable Answers Reject Mark 46.8 x 32 = 28.2 / 28.1504 (atm) 53.2 IGNORE sf except 1 Value = 28.16 if mol fraction rounded ALLOW TE from (b)(i) 28.1 46.8 x 32 = 50 29.95 (atm) Acceptable Answers Reject Mark exothermic as yield / pp of ethanoic acid / conversion of reactants/ Kp is higher at lower temperature / as equilibrium moves (right) at lower temperature ALLOW if partial pressure of ethanoic acid < 22.2 atm in (b)(ii), endothermic as yield / pp of ethanoic acid / conversion of reactants/ Kp is lower at lower temperature<br />
Question Number 19 (c)(i) Question Number 19 (c)(ii) Question Number 19 (d) Acceptable Answers Reject Mark No effect and other concentrations change to keep Kp constant / Kp is only affected by temperature/ as equilibrium moves (right) to keep Kp constant / change in pressure does not change Kp As Kp is a constant Acceptable Answers Reject Mark Yield increased to restore fraction / quotient / partial pressure ratio back to Kp ALLOW (equilibrium moves) to use up the methanol /answers based on entropy or Le Chatelier Correct prediction in (c)(i) and (c)(ii) with inadequate explanations scores 1 mark in (c)(ii) Just equilibrium moves to the right Acceptable Answers Reject Mark Answer based on car exhaust emissions Mark independently Reaction can occur at lower temperature / has lower activation energy / requires less energy (1) less fuel needed / fewer emissions (from fuels) / fewer raw materials needed / less natural resources used (1) OR Enables use of an alternative process with higher atom economy (1) fewer raw materials needed / less natural resources used (1)<br />](https://learnah.org/wp-content/uploads/2018/08/June_2010_MS_-_Unit_4_Edexcel_Chemistry_A-level_19-0.jpg)
