NJC H2 Chem 2013 Prelim P2 QP

NATIONAL JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Answer on the Question Paper. Additional Materials: Data Booklet 9647/02 Wed 4 Sept 2013 2 hours READ THE INSTRUCTIONS FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black ink in the spaces provided. You may use a soft pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid. Answers all questions. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /12 2 /16 3 /14 4 /6 5 /8 6 /16 Total /72 This document consists of 20 printed pages and 0 blank page. 104

NJC/H2 Chem/02/2013 [Turn over 2 1 Planning (P) Calcium iodate( V), Ca( IO3)2, is slightly soluble in water, approximately 4.6 g dm‒3 at 25°C. The molar enthalpy of a solution is defined as the enthalpy change when one mole of the solid dissolves in water. [ Mr of Ca(IO3)2 : 390.1] (a) (i) Predict and explain how the solubility of calcium iodate(V ) in water changes as the temperature is increased. Ca(IO3)2 (s) Ca2+ (aq) + 2IO3 ‒ (aq) ΔHsol > 0 ………………………………………………………….……………………………………. ………………………………………………………………..……………………………… ………………………………………………………………….……………………………. ………………………………………………………………………..……………………… (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. [3] (b) You are to conduct an experiment to determine as accurately as possible the concentration of a saturated solution of calcium iodate(V). You may assume you are provided with the following:  FA1: 250 cm3 suspension of calcium iodate(V)  FA2: 1.00 mol dm‒3 of potassium iodide, KI  FA3: 1.00 mol dm ‒3 sodium thiosulfate, Na2S2O3  FA4: 1.00 mol dm ‒3 hydrochloric acid, HCl For Examiner’s Use 105

NJC/H2 Chem/02/2013 [Turn over 3  Deionised water  Indicators commonly found in the laboratory  the apparatus normally found in a school or college laboratory (i) Given that acidified iodate(V ) reacts with iodide to form iodine, IO3 ‒ (aq) + 5I‒ (aq) + 6H+(aq)  3I2(aq) + 3H2O(l) With the aid of an equation, suggest how the amount of iodine produced in this reaction can be determined using only the solutions given. ………………………………………………………………………………………….….. ………………………………………………………………………………………...…… (ii) Write a plan to determine the concentration of a saturated solution of calcium iodate(V). Your plan should include the following.  preliminary calculations to determine if the given concentration of the solution you have selected in (b)(i) is suitable for use  appropriate quantities and concentrations of other solutions  a full description of the procedures you would adopt …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. For Examiner’s Use 106

NJC/H2 Chem/02/2013 [Turn over 4 …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..……….[7] (c) Show how the experimental data obtained in part (b) would be used to determine the solubility product of calcium iodate(V ). You may assume the numerical value of experimental data in (b)(ii) to be x . [2] [Total:12] For Examiner’s Use 107

NJC/H2 Chem/02/2013 [Turn over 5 2 In 1911, the French chemist F.A.V. Grignard reacted small pieces of magnesium with a warm solution of halogenoalkane, such as iodomethane or a haloarene, such as bromobenzene, in a dry, non-polar solvent and obtained a solution containing a Grignard reagent commonly written as RMgX. Grignard reagents with different alkyl or aryl groups have been prepared and are widely used in organic synthesis. A typical example of the use of a Grignard reagent is the two-step reaction of RMgX with aldehydes to form alcohols. RMgBr + R’CHO + Mg(OH)Br (a) Suggest the type of reaction which occurs in Reaction A ……………………………………………………………………………… Reaction B ……………………………………………………………………………… [2] (b) A student wanted to prepare alcohol W using a similar two-step process as shown in (a). He used pentan-2-one and a Grignard reagent. Table 1.1 shows the volatilities and hazards of the reagents and the alcohol W. Substance Volatility Hazard iodoethane moderate flammable; toxic; respiratory irritant ethoxyethane (C2H5)2O high flammable; harmful magnesium turnings non-volatile flammable pentan-2-one low flammable; harmful alcohol W very low flammable; irritant Table 1.1 (i) Identify one potential safety hazard of using these materials and state how you would minimise this risk. You may a ssume that the experimenters are wearing gloves, eye protection and lab coats. …….……………………………………………………………………………...………… ……………………..………………………………………………………………...……… RCHR' OH Reaction A Reaction B RCHR' OMgBr For Examiner’s Use 108

NJC/H2 Chem/02/2013 [Turn over 6 (ii) The day before the experiment, anhydrous calcium chloride is added to the iodoethane, sodium wire is added to the ethoxyethane and the glassware is left in an oven. Suggest the single purpose of these three precautions. …………….…….………………………………………………………………...………… …………………….………………………………………………………………...……… [2] Step I 1.50 g of magnesiu m turnings is added to a round -bottomed flask with an equimolar quantity of iodoethane and 20 cm3 of ethoxyethane. Table 1.2 gives some physical properties of the reagents and the organic product. Substance Formula Molar mass / g mol−1 Density / g cm−3 Solubility in water Boiling point / °C iodoethane C2H5I 156 1.93 slightly soluble 72 ethoxyethane (C2H5)2O 74