CIE Jun 2014 v2 Paper 5 Q1

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PMT The liquids trichloromethane and water separate into two immiscible layers when shaken together and allowed to stand. Ammonia can dissolve in both of these layers. The distribution of ammonia between these two solvents is called partition, where the concentration of ammonia in each solvent will be different. The partition coef cient represents the ratio of the distribution. You are to plan an experiment, using a titration with sulfuric acid, to determine the value of the partition coef cient of ammonia between water and trichloromethane at room temperature. The following information gives some of the hazards associated with trichloromethane and ammonia. Trichloromethane: Anaesthetic if inhaled. Dangerously irritating to the respiratory system. Ammonia: An aqueous solution with a concentration of less than 3 mol dm3 may cause harm to eyes or in a cut. At greater concentrations aqueous ammonia should not be inhaled and it causes irritation to the eyes and skin. You are provided with the following.trichloromethane aqueous ammonia of concentration 5.00 mol dm3 sulfuric acid, of concentration 0.500 mol dm3 distilled water for dilution of aqueous ammonia (a) Explain why ammonia is likely to be more soluble in water than in trichloromethane.[2] (b) De ne the partition coef cient, Kpartition, for ammonia between water and trichloromethane. State whether the partition coef cient you have de ned will be greater or less than 1. [1]UCLES 2014 9701/52/M/J/14<br /> PMT (c) In the experiment, explain whether it is important that the volumes of water and trichloromethane are the same.[1] (d) Write an equation for the reaction of aqueous ammonia and sulfuric acid.[1] (e) (i) The partition coef cient for ammonia distributed between water and trichloromethane is approximately 25. Calculate the concentration of aqueous ammonia that should be used so that a 25.0 cm3 sample of the aqueous ammonia layer would require approximately 24.026.0 cm3 of 0.500 mol dm3 sulfuric acid for complete neutralisation. Then state the factor by which the 5.00 mol dm3 aqueous ammonia should be diluted to give that concentration. [2] (ii) Describe, in detail, how you would dilute 5.00 mol dm3 aqueous ammonia to make 250 cm3 of aqueous ammonia ready for use in the experiment.[2]UCLES 2014 9701/52/M/J/14 [Turn over<br /> PMT (f) Other than the use of eye protection and gloves, state one safety precaution you would take while setting up the experiment.[1] (g) State a suitable indicator for use in the titration of a sample taken from the experiment. Explain your answer.[2] (h) It is unnecessary to titrate both layers of the partition. Explain why it would be better to titrate a sample of the aqueous layer rather than the trichloromethane layer.[1] (i) Once a mean titre has been calculated, outline the steps you would take to calculate the partition coef cient.[2] [Total: 15]UCLES 2014 9701/52/M/J/14<br /> PMT QUESTION 2 STARTS ON THE NEXT PAGE.UCLES 2014 9701/52/M/J/14 [Turn over<br />

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