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CIE Jun 2013 v1 Paper 3 Q1
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![Examiners For Use The reaction between sulfuric acid and sodium hydroxide is exothermic. H2SO4(aq) + 2NaOH(aq)Na2SO4(aq) + 2H2O(l) By measuring the temperature changes that occur when different volumes of the acid are added to axed volume of the alkali, it is possible to determine the neutralisation point. This is the point at which just enough acid has been added to react with all the alkali present. The aim of the investigation is to determine the concentration of the sulfuric acid. FA 1 is 2.00 mol dm3 sodium hydroxide, NaOH. FA 2 is dilute sulfuric acid, H2SO4. Read through the instructions carefully and prepare a table for your results before starting any practical work. (a) MethodSupport a plastic cup in a 250 cm3 beaker.Use a pipette to transfer 25.0 cm3 of FA 1 into the plastic cup.Record the temperature of FA 1, T1, in the space below. T1 = . CFill the burette labelled FA 2 with FA 2. Add 5.00 cm3 of FA 2 from the burette to the plastic cup. Stir the mixture thoroughly and record the temperature of the solution. Add a further 5.00 cm3 of FA 2 to the plastic cup and again record the temperature. Repeat the addition of 5.00 cm3 portions of FA 2 until you have added a total of 50.00 cm3 of FA 2 to the plastic cup. Measure the temperature after each addition. Record in your table below the total volume of FA 2 added and the temperature of the solution after each addition.UCLES 2013 9701/31/M/J/13 II III IV [5] [Turn over<br />
Examiners For Use (b) After each addition of acid, the temperature rise, T, is given by, T = temperature recordedT1. The total volume of solution in the plastic cup, VT is given by, VT = volume of FA 2 + volume of FA 1. The heat given out by the reaction is proportional to the temperature rise, T, multiplied by the total volume of solution in the plastic cup, VT. Use your experimental results to complete the following table. You should include:the volume of FA 2 the total volume in the plastic cup, VT the temperature of the solution the temperature rise, T the total volumethe temperature rise, (VTT)UCLES 2013 9701/31/M/J/13 [1]<br />
(c) (i) On the grid below, plot the values of (VTT) on the y-axis against the volume of FA 2 on the x-axis. Examiners For Use II III IVUCLES 2013 9701/31/M/J/13 [Turn over<br />
Examiners For Use (ii) Draw a straight line of bestt through the points where the values of (VTT) are increasing. Draw a second straight line of bestt through the points where the values of (VTT) are decreasing. (iii) From your graph, determine the volume of FA 2 where the two lines of bestt intersect. volume of FA 2 =cm3 [5] (d) The value you recorded in (c)(iii) is the volume of FA 2 which is needed to neutralise 25.0 cm3 of FA 1. In the following calculations you will determine the concentration of FA 2. Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) Calculate how many moles of sodium hydroxide are contained in 25.0 cm3 of FA 1. (ii) Calculate how many moles of sulfuric acid would react with the number of moles of NaOH in (i). moles of NaOH =mol (iii) Calculate the concentration of FA 2. moles of H2SO4 =mol concentration of FA 2 =mol dm3 [3] (e) Other than heat losses from the plastic cup to the surroundings, suggest an additional source of error in this experiment and how this error could be reduced.[1] [Total: 15]UCLES 2013 9701/31/M/J/13<br />](https://learnah.org/wp-content/uploads/2018/08/June_2013_v1_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Mark Scheme GCE AS/A LEVELMay/June 2013 Syllabus 9701 Paper 31 Question Sections Indicative material (a) PDO layout I Constructs a table for results with space for 10 volumes. Mark PDO recording II Appropriate headings and units for data given. Volumes in cm3 or / cm3 or (cm3), temperature in C or /C or (C) in table. All volumes to same dp. PDO recording III All temperatures recorded to the nearest 0.5 C both in the table and for T1. At least one ending in .0 and one in .5. MMO quality IV + V Compare temp rise for addition of 25 cm3 of [5] FA 2 with the Supervisor value. Award 2 marks for T within1 C. Award 1 mark for T within2 C. (b) ACE interpretation Correctly calculates T, VT and TVT (assume correct data from (a)) (min 8 results) [1] (c) (i) PDO layout TVT on y-axis and volume of FA 2 on x-axis. Axes clearly labelled (ignore units). II Uniform scales chosen to use more than half of each axis. Only include 0 if point plotted. Points plotted use 5 large squares vertically and 4 horizontally. III All points plotted. Examiner to check points at V = 5, 10, 15, 20 and 25. The points should be withinsmall square and in correct small square. Min 8 (c) (ii) IV Draws both straight lines of best fit. (c) (iii) ACE interpretation Reads correctly the value of FA 2 from the intercept of the two lines. Answer within 0.5 cm3. Ignore sf. [5] (d) (i) (d) (ii) (d) (iii) 0.0500 mol (Allow 0.050) 0.0250 mol (allow 0.025) Allow ecf from (i)/2 1000(d)(ii) / (c)(iii) (24 sf) Allow ecf from (ii). Penalise sf once only. [3]Cambridge International Examinations 2013<br />
Page 3 (e) Mark Scheme GCE AS/A LEVELMay/June 2013 Syllabus 9701 Paper 31 ACE improvements [1] Accuracy of temperature measurementuse a 0 to 50 C thermometer or a thermometer with smaller scale divisions (not just more accurate/ electronic thermometer/parallax). Uncertainty about where the lines crosssample more values of FA 2 in the region of the intersection. Repeat/ extra readings on LHS of intersection/ near maximum. Initial temperatures of acid and alkali not samemeasure both. Other answers acceptable if specific. [Total: 15] 2 (a) MMO collection Initial and final volumes recorded for rough AND initial, final and volume added recorded for accurate titre. PDO recording II All accurate readings recorded to 0.05 cm3. Do not award if 50(.00) is used as an initial burette reading; more than one final burette reading is 50.(00); any burette reading is greater than 50.(0). MMO decision III Two uncorrected accurate titres within 0.1 cm3. Do not award if, having performed 2 titres within 0.1 cm3, a further titration is performed that is >0.1 cm3 from the closer of the original 2 titres unless a further titration has been carried out which is within 0.1 cm3 of any other. MMO quality IV + V Award 2 marks if difference from Supervisor [5] within 0.20 cm3. Award 1 mark if difference from Supervisor within 0.50 cm3. Examiner compares candidate mean titre with Supervisor mean titre. If best titres are0.5 cm3, cancel one of the Q marks.Cambridge International Examinations 2013<br />](https://learnah.org/wp-content/uploads/2018/08/June_2013_v1_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
