Edexcel Jun 2014 (IAL) Paper 5 Q23 (with explained solutions) |

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Edexcel Jun 2014 (IAL) Paper 5 Q23

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23 10 cm3 of a gaseous hydrocarbon, CxHy, was mixed with excess oxygen and ignited. The total gas volume was measured at room temperature and pressure before and after combustion, and it was found that it had contracted by 20 cm3. On shaking the remaining gases with excess potassium hydroxide solution, the total gas volume contracted by a further 40 cm3. The equation for the complete combustion of CxHy is CxHy + (x + (y/4))O2 (cid:314) xCO2 + (y/2)H2O (a) Explain why the volume of gas contracts after combustion. (1)(b) Explain why the volume of gas contracts after shaking with excess potassium hydroxide. (1)(c) Calculate the molecular formula of CxHy. (3) (Total for Question 23 = 5 marks) TOTAL FOR SECTION B = 50 MARKS 24 *P42979A02432*<br />
BLANK PAGE *P42979A02532* 25 Turn over<br />

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Question Number Acceptable Answers 23(a) Volume of CO2 is less than volume of oxygen (and only other product is water). OR Fewer moles / molecules of gaseous products (than reactants). Question Number Acceptable Answers 23(b) Potassium hydroxide / KOH absorbs CO2 OR CO2 reacts with potassium hydroxide / KOH OR CO2 dissolves in potassium hydroxide / KOH Question Number Acceptable Answers 23(c) So 10x = 40 x = 4 (1) So 10 + 10(x + (y/4))10x = 20 10(y/4) = 10 y = 4 (1) CxHy = C4H4 (1) Correct formula with no working or explanation scores 3 Total for Question 23 = 5 marks Total for Section B = 50 marks Reject Mark Reject Mark Reject Mark WCH0501 1406<br />

Question 19 20 21 22 23 24

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