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Edexcel Jun 2012 Paper 4 Q16
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![16 Iodine reacts with propanone in the presence of an acid catalyst. CH3COCH3(aq) + I2 DT &+3COCH2I(aq) + HI(aq) $QH[SHULPHQWZDVFDUULHGRXWWRLQYHVWLJDWHWKHNLQHWLFVRIWKLVUHDFWLRQEPRQLWRULQJ the concentration of iodine. The progress of the reaction was followed by mixing together the reagents, removing samples of the mixture every five minutes, quenching the reaction and then titrating to find the concentration of iodine at a given time. (a) (i) Suggest a suitable reagent with which you could titrate the iodine. (1)(ii) State and explain how you would quench the reaction. (2)(b) (i) Data obtained from the experiment are shown in the table below. Use the data to plot a suitable graph to determine the order of the reaction with respect to iodine and state this order. (3) Time / mins [I2(aq)] / mol dm 25 u u u u u 8.55 u 16 *P39308A01624*<br />
[I2(aq)] / mol dm Time / minutes Order with respect to iodine*P39308A01724* 17 Turn over<br />
(ii) Explain how you determined the order using your graph. (2)(c) State an alternative practical procedure that could be used to monitor the concentration of iodine. (1)(Total for Question 16 = 9 marks) 18 *P39308A01824*<br />](https://learnah.org/wp-content/uploads/2018/08/l_smalljpgJune_2012_QP_-_Unit_4_Edexcel_Chemistry_A-level_16-0.jpg)
![Reject Mark Just thiosulfate Reject Mark NaOH/ sodium hydroxide/ alkali just cold water Reject Mark Question Number 16 (a)(i) Correct Answer Sodium thiosulfate/Na2S2O3 ALLOW S2O3 2- or thiosulfate ions Question Number 16(a)(ii) Add (excess) sodium hydrogencarbonate/ Acceptable Answers NaHCO3 (1) To neutralize/remove/react with acid (catalyst) (1) Cool in ice (water) with no reference to neutralizationallow 1 mark but ignore if either of first two marks awarded Question Number 16(b)(i) Suitable graph and scale (1) Acceptable Answers Points plotted and line of best fit (1) 0 order (with respect to iodine) (1)<br />
Reject Mark Half life is constant Acceptable Answers Reject Mark Colorimetry/use of pH meter/conductivity/titrate with AgNO3/titrate with alkali (to monitor change in [H+]) Calorimetry Use of starch/ Iodine clock reaction Question Number 16(b)(ii) Graph is a straight line/Gradient is Acceptable Answers constant (1) Rate stays constant (as iodine used up)/ Concentration has no effect on rate (1) Stand alone marks Question Number 16(c)<br />
Correct Answer Methyl propanoate ALLOW methy or methly for methyl Acceptable Answers Question Number 17(a)(ii) Toxic (steamy/misty) fumes/ toxic HCl(gas)/corrosive HCl(gas)/toxic propanoyl chloride/lachrymatory propanoyl chloride (1) So use in a fume cupboard (1) OR Corrosive Propanoyl chloride is (1) So wear gloves when handling (1) Mark Mark Reject Reject HCl(aq)/ hydrochloric acid Just harmful/irritant Just harmful/irritant Reject Mark Question Number 17 (a)(i) Question Number 17(b) Acceptable Answers Table 0.31, 0.16, 1.41 all 3 scores 2, 2 out of 3 scores 1, 1 or 0 out of 3 scores 0 (2) Kc = (0.21/V) x (1.41/V) (0.16/V) x (0.31/V) Kc = 5.969758 Kc = 5.97 (1) IGNORE sf except 1 IGNORE any units ALLOW TE from incorrect values in table. TOTAL FOR SECTION B = 52 MARKS<br />](https://learnah.org/wp-content/uploads/2018/08/June_2012_MS_-_Unit_4_Edexcel_Chemistry_A-level_16-0.jpg)
