CIE Nov 2013 v3 Paper 5 Q3

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In the fractional distillation of two liquids which are miscible (dissolve in each other) in all proportions the more volatile of the two will distilrst. At any temperature the composition of the vapour in equilibrium with the liquid has a higher proportion of the more volatile component which has a lower boiling point. Examiners For Use An experiment was carried out tetrachloromethane, CCl 4,and tetrachloroethane, C2H2Cl 4. investigate to the boiling points of mixtures of A convenient method for representing the composition of the mixtures, both liquid and vapour, is to use the concept of mole fraction. For example, if the liquid mixture consists of 0.15 mole of liquid A and 0.35 mole of liquid B, the mole fraction of A is 0.15 i.e. 0.30. (0.15 + 0.35) (a) The results of several of these experiments are recorded below. temperature / C 120.0 108.5 99.3 93.0 89.3 83.3 79.9 76.0 mole fraction CCl 4 liquid mole fraction CCl 4 vapour 0.000 0.100 0.200 0.300 0.400 0.600 0.800 1.000 0.000 0.469 0.552 0.800 0.861 0.918 0.958 1.000 Calculate the relative molecular masses (Mrs) of CCl 4 and C2H2Cl 4. [Ar: H, 1.0; C, 12.0; Cl, 35.5] [1] (b) (i) The vapour from the equilibrium at 108.5 C was analysed and found to consist of 7.22 g of CCl 4 and 8.92 g of C2H2Cl 4. Show clearly by calculation that this gives a mole fraction of 0.469 for CCl 4 vapour. (ii) The vapour from the equilibrium at 83.3 C was analysed and found to consist of 14.14 g of CCl 4 and 1.38 g of C2H2Cl 4. Show clearly by calculation that this gives a mole fraction of 0.918 for CCl 4 vapour.UCLES 2013 9701/53/O/N/13 [2]<br /> (c) On the same axes, plot two graphs, one for the liquid and one for the vapour, to show the variation in temperature (y-axis) with the mole fraction compositions (x-axis) of both the liquid and the vapour. Draw two lines of bestt. Each line could be either a curved line or a straight line.UCLES 2013 9701/53/O/N/13 [4] [Turn over<br /> Examiners For Use (d) Circle and label on the graph the point you consider to be the most anomalous. Do not circle or label any other point. If it is assumed that the analysis was carried out accurately, suggest a reason why the point might be anomalous.[2] (e) By drawing an appropriate construction line on your graphs, determine the mole fraction of CCl 4 in the vapour which is in equilibrium with a liquid with a mole fraction of 0.500 CCl 4. (f) The temperatures were measured using a thermometer calibrated in 0.1 C graduations. If the thermometer had only been calibrated in 1.0 C graduations, calculate the percentage errors which would result from the determination of the boiling points of each of the two pure liquids. [2] [2]UCLES 2013 9701/53/O/N/13<br /> Examiners For Use (g) (i) Use your graphs to state whether CCl 4 or C2H2Cl 4 distillsrst from a mixture of the two liquids.(ii) Explain your answer (i).[2] [Total: 15]UCLES 2013 9701/53/O/N/13 [Turn over<br />

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