CIE Jun 2017 v2 Paper 3 Q2 (with explained solutions) |

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CIE Jun 2017 v2 Paper 3 Q2

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You are to determine the enthalpy change of neutralisation for a different acid from that used in Question 1. The acid is represented by HB where B represents the anion. HB(aq) + NaOH(aq) NaB(aq) + H2O(l) PMT FB 3 is 2.00 mol dm3 acid, HB. FB 4 is 72.00 g dm3 sodium hydroxide, NaOH. (a) Method Read through the method before starting your practical work and prepare a table below for recording your results. Experiment 1Place the plastic cup in the 250 cm3 beaker. Pour 25 cm3 of FB 3 into the larger measuring cylinder. Measure and record the temperature of FB 3. Rinse and dry the thermometer. Use the smaller measuring cylinder to transfer 25 cm3 of FB 4 into the plastic cup. Measure and record the temperature of FB 4. Add the 25 cm3 of FB 3 to FB 4 in the plastic cup and stir the mixture. Measure and record the highest temperature reached. Calculate and record the average initial temperature of the solutions. Calculate and record the temperature rise. Empty the plastic cup, rinse it with water and shake it to remove excess water. Experiment 2Repeat the method given for Experiment 1 using 50 cm3 of each solution. Use the larger measuring cylinder for FB 3 and the smaller measuring cylinder for FB 4. Results II III IV [4]UCLES 2017 9701/32/M/J/17 [Turn over<br />
PMT (b) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Show by calculation that in Experiment 1, the number of moles of acid was in excess of the number of moles of sodium hydroxide. (ii) Calculate the heat energy evolved in Experiment 1. [Assume that 4.2 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 C.] (iii) Calculate the enthalpy change, in kJ mol1, for Experiment 1. heat energy evolved =J (iv) Calculate the number of moles of sodium hydroxide neutralised in Experiment 2. enthalpy change =kJ mol1 (sign) (value) (v) Calculate the enthalpy change, in kJ mol1, for Experiment 2. moles of NaOH =mol enthalpy change =kJ mol1 (sign) (value) [5]UCLES 2017 9701/32/M/J/17<br />
PMT (c) (i) The accuracy of the larger measuring cylinder is0.5 cm3. The accuracy of the smaller measuring cylinder is0.25 cm3. Calculate the maximum percentage error in the measurement of the volume of FB 3 used in Experiment 2 and the measurement of the volume of FB 4 used in Experiment 2. Show your working. maximum % error in volume of FB 3maximum % error in volume of FB 4(ii) Suggest a change to the method used in (a) that would improve the accuracy of your results.[3] [Total: 12]UCLES 2017 9701/32/M/J/17 [Turn over<br />

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9701/32 Question 1(c)(ii) 1(c)(iii) 1(c)(iv) 1(d)(i) 1(d)(ii) Cambridge International AS/A LevelMark Scheme PUBLISHED Answer Correctly calculates 0.0025 x 1000 to 3 or 4 sf ) Correct expression 12.6(ii) Anion in FB 1 = CHCl2COO (allow ecf: for candidates answer to (iii)) CH3COO :77 CCl3COO :146.5 CH2ClCOO : 77.5111.5 CHCl2COO : 112146 Conc NaOH lower = > titre smaller = > smaller Mr No effect on identification unless closer to smaller mass acid or (different Mr may lead to the) identification of a different acid with matching / close to Mr Question 2(a) 2(b)(i) Answer I Unambiguous headings and correct units tabulated for all 6 thermometer readings, mean temps, and Ts II All thermometer readings recorded to 0.5 C and Ts correctly calculated and Mean temperatures correctly calculated to nearest .5 C or to 1 or 2 dp Award III if candidate Ts within 1.5 C Award III and IV if candidate Ts within 1.0 C Correctly calculates n acid = 0.05(0) mol and n NaOH = 0.045 molUCLES 2017 Page 4 of 9 PMT May/June 2017 Marks 1 1 1 1 1 Total: 14 Marks 1 1 1 1 1<br />
Cambridge International AS/A LevelMark Scheme PUBLISHED Answer Correctly calculates 504.2T1 to minimum 2 sf ii ( ) 1000 x 0.045 Correct expression 2mol NaOH in (i) or 0.09(0) in (iv) and Correctly uses 100 x 4.2 x T 2 (1000 x iv in (v) Negative signs shown in (iii) and (v) and final answers to 24 sf in (ii), (iii) & (v) % error in vol of FB 3 = 0.5 x 100 = 1.(0)% 50 % error in vol of FB 4 = 2 x 0.25 x 100 25 = 2.(0)% Use a burette / pipette for volume measurements / instead of a measuring cylinder or Add a lid to reduce heat loss (by convection) / to reduce convection or Use thermometer reading to 0.2 C / smaller divisions / calibrations / more sensitive 9701/32 Question 2(b)(ii) 2(b)(iii) 2(b)(iv) +(v) 2(c)(i) 2(c)(ii) PMT May/June 2017 Marks 1 1 1 Total 12UCLES 2017 Page 5 of 9<br />

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