CIE Jun 2016 v3 Paper 5 Q2

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Activation energy, EA, is the minimum energy with which particles must collide so that a reaction occurs. The activation energy for the reaction of magnesium with aqueous hydrogen ions can be determined in the laboratory. Mg(s) + 2H+(aq)Mg2+(aq) + H2(g) PMT A magnesium strip is placed in dilute hydrochloric acid and the time taken (t), in seconds, for the magnesium to disappear is measured. The initial rate of reaction is calculated as time If the experiment is repeated at several different temperatures then the following mathematical relationship can be used to calculate EA. log10 1 1 1 t` j.1 T` t` j = 0.0191 T is the temperature measured in K. 1 t is the initial rate of reaction in s1. A graph of log10 1 t` j against 1 T can be plotted. Experimental procedure 1. 2. 3. 4. 25 cm3 of dilute hydrochloric acid is added to a boiling tube. The boiling tube is placed in a water bath until the dilute hydrochloric acid reaches a constant temperature. This temperature is recorded. A magnesium strip of mass 0.10 g is added to the boiling tube, the mixture stirred and the time taken for the magnesium to disappear is recorded. The temperature of the water bath is changed and the experiment is repeated.UCLES 2016 9701/53/M/J/16 [Turn over<br /> PMT (a) The results of this experiment, carried out at different temperatures, are recorded in the table below. Process the results to calculate the reciprocal of temperature 1 T` value of 1 T has been done for you. j and log10 1 t` j. The first Record 1 T in standard form to three significant figures. Record log10 1 t` j to two decimal places. You should expect log10 1 t` j to be negative. temperature / C time, t / s temperature, T / K 1 T / K1 1 t / s1 log10 1 t` j 15 20 27 30 34 38 40 43 48 55 83 58 36 28 18 19 15 12 9 8 288 293 300 303 307 311 313 316 321 328 3.47103 1.20102 1.72102 2.78102 3.57102 5.56102 5.26102 6.67102 8.33102 1.11101 1.25101 (b) Plot a graph on the grid on page 7 to show the relationship between log10 1 t` j and 1 T . Use a cross () to plot each data point. Draw a line of best fit. [3] [2]UCLES 2016 9701/53/M/J/16<br /> 1 T / K1 3.3103 3.4103 3.5103 3.6103 3.0103 0.8 3.1103 3.2103 PMT 1 log10 ` j t 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0UCLES 2016 9701/53/M/J/16 [Turn over<br /> PMT (c) On your graph, circle the two points you consider to be the most anomalous. Label each one with a different letter. Explain what may have caused each of the anomalies you have identified, giving a different reason each time. Make it clear in your answer to which point you are referring.[2] (d) (i) Determine the gradient of your graph. State the co-ordinates of both points you used for your calculation. Record the value of the gradient to three significant figures. co-ordinates 1co-ordinates 2(ii) Use your gradient from (i) and the mathematical relationship on page 5 to calculate the activation energy, EA, in kJ mol1. Include a sign in your answer. gradient =[2] EA =kJ mol1 [2] (e) State whether you consider the results to be reliable. Explain your answer.[1]UCLES 2016 9701/53/M/J/16<br /> PMT (f) Student X commented that data collected at higher temperatures in the experiment may be less accurate than that collected at lower temperatures. State whether student X is correct. Explain why.[1] (g) If the magnesium strip is not stirred it floats to the surface of the hydrochloric acid. State how this will affect the reaction time. Explain why.[1] (h) The experiment in (a) is repeated using dilute ethanoic acid instead of dilute hydrochloric acid. The concentration of both acids is equal. The same temperatures are used as in (a). State the effect this change in acid will have on the initial rate values. Give a reason for this.[1] [Total: 15]UCLES 2016 9701/53/M/J/16 [Turn over<br />

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