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CIE Jun 2015 v4 Paper 3 Q2
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![You are to determine the enthalpy change of solution, in kJ mol1, of ammonium chloride. FB 3 is approximately 9 g of solid ammonium chloride, NH4Cl. distilled water (a) Method Read through the instructions carefully and prepare a table below for your results before starting any practical work.Weigh the plastic cup and record the balance reading. Add between 2.9 and 3.1 g of ammonium chloride, FB 3, and record the new balance reading. Place the plastic cup in the 250 cm3 beaker. Pour 25 cm3 of distilled water into the measuring cylinder. Place the thermometer in the water and record the initial temperature in the table of results. Pour the 25 cm3 of distilled water into the plastic cup. Stir the contents of the cup and record the lowest temperature of the solution. Tilt the cup if necessary to ensure the thermometer bulb is fully immersed. Repeat the procedure using the other plastic cup. Use between 4.9 and 5.1 g of FB 3 for this experiment. Record the mass of FB 3 used and the change in temperature for each experiment. Results II III IV [5]UCLES 2015 9701/34/M/J/15<br />
(b) (i) Calculate the mean mass of FB 3 used. Give your answer to two decimal places. (ii) Calculate the mean temperature change. Give your answer to one decimal place. mean mass of FB 3 =g mean temperature change =C [2] (c) Calculations Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) Calculate the number of moles of NH4Cl present in the mass of FB 3 calculated in (b)(i). [Ar: H, 1.0; N, 14.0; Cl, 35.5] moles of NH4Cl =mol (ii) Use your answers to (b)(ii) and (c)(i) to calculate the enthalpy change of solution, in kJ mol1, of NH4Cl. (Assume that 4.2 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 C.) enthalpy change =kJ mol1 (sign) (value) [4]UCLES 2015 9701/34/M/J/15 [Turn over<br />
(d) (i) Which of the two experiments in (a), therst or the second, had the greater percentage error in the value calculated for the temperature change?(ii) Given that the error in a single thermometer reading is 0.5 C, calculate the percentage error in the temperature change for the experiment you gave in (d)(i). percentage error =% [1] (e) (i) A student suggested that it would have been better to calculate the enthalpy change for each experiment separately. What would be the advantage of this suggestion? Explain your answer fully.(ii) Another student suggested that the procedure would be improved by covering the plastic cup with a lid. Explain whether this would improve the procedure.[2] [Total: 14]UCLES 2015 9701/34/M/J/15<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v4_QP_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
![Page 3 Question Cambridge International AS/A LevelMay/June 2015 9701 34 Mark Scheme Syllabus Paper Indicative material Mark Total (iii) (c)(ii)1000 / 25 and answer expressed to 3 or 4 sf. (iv) Correct expression is shown (c)(iii) 1000 / 5.91 [3] [1] [12] (d) Total (a) 15(c)(iv)100 / 15 or 15(c)(iv)100 / (c)(iv) (Table of) results with unambiguous headings (not weight) showing4 balance readings 4 thermometer readings 2mass FB 3 added 2T II All balance readings recorded to the same number of dp (at least one dp) and thermometer readings to .0 or .5 C (minimum 2 of each) III Masses of FB 3 used between the limits given in the question (2.9(0) to 3.1(0) g and 4.9(0) to 5.1(0) g) Examiner corrects thermometer readings to the nearest 0.5 C, checks subtractions then calculates T1m2 / where T1 is the smaller temperature fall. T2m1 Award IV if ratio falls between 0.85 and 1.15 Award IV and V if ratio falls between 0.95 and 1.05 (b) (i) mean mass correctly calculated from weighings to 2 dp (ii) mean temperature fall correctly calculated from thermometer (c) (i) readings to 1 dp Do not award if values used for calculating mean are from incorrect subtractions. Correctly calculates (b)(i) / 53.5 [5] [2] 1 1Cambridge International Examinations 2015<br />
Cambridge International AS/A LevelMay/June 2015 9701 34 Mark Scheme Syllabus Paper Indicative material Mark Total Page 4 Question (ii) Correct overall expression 254.2(b)(ii) (c)(i)1000fully correct = 2 marks one error = 1 mark two errors = 0 marks 1 1 [4] [1] [2] [14] 2 1( 1000 may be awarded from use to reach final answer) Sign is + and final answers to (i) and (ii) are to 24 sf (d) (ii) (e) (i) Expression (1.0 / smaller T)100 or correct answer Advantages: any one of two values to check concordance / check whether further experiments should be carried out / find out whether mass added is proportional to T / compare the two answers (ii) No improvement as T drops so no heat loss (by convection) / as reaction is endothermic Improvement as prevents heat gain from OR surroundings Total (a) FB 4 = MnCl 2(aq); FB 5 = MgSO4(aq) ; FB 6 = NH4Fe(SO4)2 (s) Correct observations for FB 4 and FB 5 in (i) Correct observations for FB 4 and FB 5 in (ii) and correct observations for FB 4 and FB 5 in (iii).Cambridge International Examinations 2015<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v4_MS_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
