CIE Jun 2013 v2 Paper 5 Q1

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Examiners For Use Calcium hydroxide, Ca(OH)2, is slightly soluble in water, approximately 1 g dm3 at 25 C. The molar enthalpy of solution of a solid is de ned as the enthalpy change when one mole of the solid dissolves in water. (a) (i) Predict how the solubility of calcium hydroxide in water changes as the temperature is increased. Explain this prediction using Le Chateliers Principle in terms of the equilibrium between the solid calcium hydroxide and the aqueous solution, as shown in the equation below. Ca(OH)2(s) Ca2+(aq) + 2OH(aq) Hsoln = 16.7 kJ mol1 Predict how the solubility will change as the temperature is increased.Explanation(ii) Display your prediction in the form of a sketch graph between 0 C and 100 C. Label the axes with units and give numerical values to ensure that the line clearly shows the solubility at 25 C. 0 0 [4] (b) If you were to carry out an experiment to investigate how the solubility of calcium hydroxide varies as the temperature increases name, (i) the independent variable,(ii) the dependent variable.[1]UCLES 2013 9701/52/M/J/13 [Turn over<br /> Examiners For Use (c) You are to plan an experiment to determine as accurately as possible the concentration of a saturated aqueous solution of calcium hydroxide by titration with hydrochloric acid. You are reminded that the approximate solubility of calcium hydroxide is 1 g dm3 at 25 C. The following information gives some of the hazards associated with calcium hydroxide and hydrochloric acid. Hydrochloric acid, HCl (aq) Corrosive; Causes burns: Irritating to respiratory system. Solutions equal to or more concentrated than 6.5 mol dm3 are corrosive. Solutions equal to or more concentrated than 2 mol dm3 but more dilute than 6.5 mol dm3 are said to be irritant. Calcium hydroxide, Ca(OH)2(s) Irritant; risk of serious damage to eyes. You are provided with the following materials: 250 cm3 of saturated calcium hydroxide, 50 cm3 of 2.00 mol dm3 hydrochloric acid. Give a step-by-step description of how you would carry out the experiment by including: (i) a balanced equation for the reaction between aqueous calcium hydroxide and hydrochloric acid, (ii) a list of apparatus with volumes where appropriate, (iii) (iv) (v) (vi) (vii) a suitable indicator with relevant colours, a calculation of the approximate concentration of a saturated aqueous solution of calcium hydroxide in mol dm3 at 25 C, [Ar: H, 1.0; O, 16.0; Ca, 40.1] a detailed method for the dilution of the hydrochloric acid such that when a titration is carried out the two reacting volumes are approximately equal at the end-point. The relevant calculations and reasoning must be shown in full. a detailed method for carrying out suf cient titrations to allow an accurate end-point to be obtained, an outline calculation to show how the results are to be used to determine the accurate concentration of the aqueous calcium hydroxide. [Ar: Cl, 35.5]UCLES 2013 9701/52/M/J/13<br /> Examiners For UseUCLES 2013 9701/52/M/J/13 [Turn over<br /> Examiners For Use[8] (d) State one hazard that must be considered when planning the experiment and describe a precaution that should be taken to keep risks from this hazard to a minimum. You should use the information in (c).[2] [Total: 15]UCLES 2013 9701/52/M/J/13<br /> QUESTION 2 STARTS ON THE NEXT PAGE.UCLES 2013 9701/52/M/J/13 [Turn over<br />

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