CIE Jun 2016 v2 Paper 5 Q2

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The relative molecular mass, Mr, of volatile liquids can be determined using the apparatus below. steam in gas syringe self-sealing cap volatile liquid PMT hypodermic syringe steam jacket thermometer steam out A known mass of volatile liquid is injected into the gas syringe using a hypodermic syringe. The injected volatile liquid vaporises and the volume of vapour is recorded. The experiment can be repeated using different samples of the same volatile liquid. The following mathematical relationship can be used to calculate the relative molecular mass if the experiment is carried out at 100 C and 1.01105 Pa. V = 3.07104 Mrm m is the mass of the volatile liquid in g. V is the volume of the volatile liquid in cm3 when vaporised. A graph of V against m can be plotted. A group of students is given a volatile liquid hydrocarbon, Y, and asked to find its relative molecular mass in a series of experiments using this procedure.A 100 cm3 gas syringe is placed in a steam jacket. Approximately 5 cm3 of air is pulled into the gas syringe. The temperature is allowed to reach a constant 100 C. Once the air in the gas syringe has stopped expanding, its volume is recorded. The hypodermic syringe is filled with liquid Y. The total mass of the hypodermic syringe and liquid Y is recorded. A little liquid Y is injected into the hot gas syringe. The total mass of the hypodermic syringe is recorded again. The maximum volume of air and vapour in the gas syringe is recorded. The mass of liquid Y injected into the gas syringe is calculated and recorded.UCLES 2016 9701/52/M/J/16 [Turn over<br /> The results from the group of students are given in the table. PMT mass of syringe + liquid Y mass of syringe + liquid Y before injection after injection volume of air in gas syringe before injection / cm3 volume of air + vapour Y in gas syringe after injection / cm3 mass of liquid Y used / g volume of vapour Y / cm3 7 9 13 11 14 8 9 12 7 11 55 44 85 69 97 39 79 91 48 84 / g 4.68 5.23 4.64 4.92 5.07 5.48 5.12 4.94 4.72 4.83 / g 4.83 5.33 4.85 5.09 5.31 5.57 5.32 5.17 4.84 5.05 (a) Process the results in the table to calculate both the masses of volatile liquid Y used and the [2] volumes of vaporised Y. (b) Plot a graph on the grid on page 9 to show the relationship between mass of liquid Y and volume of vapour Y. Use a cross () to plot each data point. Draw the line of best fit. [2]UCLES 2016 9701/52/M/J/16<br /> PMT 90 80 70 volume of vapour Y / cm3 60 50 40 30 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 mass of liquid Y / gUCLES 2016 9701/52/M/J/16 [Turn over<br /> PMT 10 (c) Liquid Y evaporates easily, even at room temperature. This can cause anomalous results giving points below the line of best fit. (i) Explain how such anomalies occur.[1] (ii) With reference to the experimental procedure, explain how this source of error could be minimised.[1] (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 the gradient value in (i) and the mathematical relationship on page 7 to calculate the experimentally determined relative molecular mass of Y. gradient =[2] experimentally determined Mr of Y =[2]UCLES 2016 9701/52/M/J/16<br /> (e) Compound Y is a hydrocarbon that contains 85.7% carbon by mass. The diagram shows the mass spectrum of compound Y. 11 PMT relative abundance / % 100 80 60 40 20 10 20 30 40 60 70 80 90 100 50 m / e Use all the information given to determine the molecular formula of Y. molecular formula of Y[2] [Total: 12]UCLES 2016 9701/52/M/J/16 [Turn over<br />

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