CIE Jun 2013 v4 Paper 3 Q1

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When aqueous hydrochloric acid is mixed with aqueous sodium hydroxide, the neutralisation reaction releases heat causing a rise in the temperature of the solution. Examiners For Use HCl (aq) + NaOH(aq)NaCl (aq) + H2O(l) In this experiment you will mix different volumes of hydrochloric acid and sodium hydroxide but the total volume will be kept constant. For each mixture you will record the temperature rise. Since the combined volume remains the same, the temperature rise is a direct measure of the heat given out by the reaction. The maximum heat given out occurs when all the acid present is exactly neutralised by all the alkali present. By determining the volumes when this occurs you can work out the concentration of the sodium hydroxide. FB 1 is 2.00 mol dm3 hydrochloric acid, HCl. FB 2 is aqueous sodium hydroxide, NaOH. Read through the instructions carefully and prepare a table for your results in the space on page 4 before starting any practical work. (a) Method Experiment 1Support the plastic cup in the 250 cm3 beaker. Fill the unlabelled burette with FB 1. Run 26.00 cm3 of FB 1 from the burette into the plastic cup. Record the temperature of FB 1, T1, in the space below.Fill the burette labelled FB 2 with FB 2. Run 4.00 cm3 of FB 2 from the burette into the plastic cup. Stir the mixture thoroughly and record in your table the maximum temperature of the solution. Empty the plastic cup, rinse thoroughly with water and shake dry. T1 = . C Experiment 2Support the plastic cup in the 250 cm3 beaker. Run 22.00 cm3 of FB 1 from the burette into the plastic cup. Run 8.00 cm3 of FB 2 from the burette into the plastic cup. Stir the mixture thoroughly and record in your table the maximum temperature of the solution. Empty the plastic cup, rinse thoroughly with water and shake dry.UCLES 2013 9701/34/M/J/13 [Turn over<br /> Experiments 37Repeat the experiment using 18.00, 14.00, 10.00, 6.00 and 2.00 cm3 of FB 1 respectively. Add sufficient FB 2 each time to make sure that the total volume remains 30.00 cm3. For each of your seven experiments, record in the space belowthe volume of FB 1, the volume of FB 2, the maximum temperature of the solution, the temperature rise, T, where T = maximum temperature recordedT1. Examiners For Use [6] (b) (i) On the grid opposite, plot the temperature rise, T, on the y-axis against the volume of FB 1 on the x-axis. The scale for T should extend at least 2 C above your greatest temperature rise. (ii) Draw a straight line of bestt through the points where the values of T are increasing. Draw a second straight line of bestt through the points where the values of T are decreasing. (iii) From your graph, determine the value of the volume of FB 1 where the two lines of bestt intersect. volume of FB 1 =cm3 [5] II III IV VI II III IVUCLES 2013 9701/34/M/J/13<br /> Examiners For UseUCLES 2013 9701/34/M/J/13 [Turn over<br /> Examiners For Use (c) Calculations Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) Calculate how many moles of hydrochloric acid are contained in the volume recorded in (b)(iii). (ii) Calculate how many moles of sodium hydroxide would react completely with the number of moles of hydrochloric acid in (c)(i). moles of HCl =mol (iii) Calculate the concentration of FB 2. Remember that the combined volume of FB 1 and FB 2 in each experiment was 30.00 cm3. moles of NaOH =mol concentration of FB 2 =mol dm3 [3] II III (d) A student decided to modify the experiment. The total volume of the solution was increased to 50 cm3 and temperature rises were recorded for 5, 10, 15, 20, 25, 30, 35, 40 and 45 cm3 of FB 2. The volumes were measured using a 50 cm3 measuring cylinder. Discuss how these changes would affect the accuracy with which the concentration of FB 2 could be determined.[2] [Total: 16]UCLES 2013 9701/34/M/J/13<br />

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