VJC H2 CHEM P2 Prelim

 VJC 2011 9647/02/PRELIM/11 [Turn over   2 Answer all the questions in the space provided. 1 Planning An acid can be represented by the general formula, H xA, where x represents the basicity of the acid. A bottle of a dilute aqueous solution of an acid, either monobasic or dibasic, was found. However, the label on the bottle had been damaged. Only the concentration of the acid, 1.00 mol dm3 was readable. A student was given a 1.00 mol dm 3 sodium hydroxide solution. She was asked to determine the basicity of the acid in the bottle by mixing different volumes of the acid and sodium hydroxide. (a) (i) Write an equation to repr esent the enthalpy change of neutralization between sodium hydroxide and HxA. ……………………………………………………………………………………. (ii) A student determined the basicity of the acid by performing the following experiments: Experiment 1: 30 cm 3 of HxA(aq) was added to 60 cm3 of NaOH(aq) Experiment 2: 60 cm 3 of HxA(aq) was added to 30 cm3 of NaOH(aq) The changes in temperature of the mixture were measured for Experiment 1 and Experiment 2 as T1 and T2 respectively. Suggest and explain the basicity of H xA if T1 = 2 x T2. [ 3 ]

 VJC 2011 9647/02/PRELIM/11 [Turn over   3 (b) For this part, you may assume that the acid is a monobasic acid, HA. A student decided to determine whether the acid, HA, is a strong or weak acid by performing a series of experimen ts involving mixing of hydrochloric acid with sodium hydroxide and HA with sodium hydroxide. Explain how, from the suggested exper iment, the student might be able to determine whether HA is a strong or weak acid. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ……………………………………………………………………………………... [2] FA 1 is a solution of sodium hydroxide of unknown concentration. FA 2 is 1.0 mol dm 3 of hydrochloric acid. Since neutralization reaction is exothe rmic, a series of experiments can be performed by mixing different volumes of FA 1 and FA 2 to determine the concentration of sodium hydroxide. (c) (i) Write a procedure to determine the temperature changes for the series of reactions between FA 1 and FA 2. Your answers should include choice of apparatus to measure the volume and temperature of the solutions. Give suitable headings for the columns numbered 1 to 5 as part of the plan of the experiment. Headings for 1: ………………………………………………………………………………. 2: ………………………………………………………………………………. 3: ………………………………………………………………………………. 4: ………………………………………………………………………………. 5: ………………………………………………………………………………. Volume of FA 1 /cm 3 Volume of FA 2 /cm3 1 2 3 4 5 30.00 40.00 33.00 37.00 36.00 34.00 40.00 30.00 44.00 26.00 48.00 22.00 50.00 20.00

 VJC 2011 9647/02/PRELIM/11 [Turn over   4 Procedure ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... (ii) The following points were plotted on a grid after an experiment. Draw a suitable graph through the plotted points. 15.0 14.0 13.0 12.0 11.0 10.0 ∆T /°C 9.0 30 50 454035 Volume of FA1 /cm3

 VJC 2011 9647/02/PRELIM/11 [Turn over   5 (iii) By using the graph in (ii), calculate the concentration of sodium hydroxide in the experiment. [7] [Total: 12]     2 Oxoanions of Group VII elements have the general formula XOm , where m = 1, 2, 3 or 4. These oxoanions are strong oxidizing agents. (a) Explain why fluorine does not form oxoanions. ……………………………………………………………………………………..………….. ………………………………………………………………………………………………… ……………………………………………………………………………………………... [2] (b) 1.25 x 10 3 mol of a bromate salt containing the BrO m  anion was added to excess potassium iodide. The resultin g mixture was washed with chloroform to dissolve the iodine, and the aqueous and organic layers were separated. Silver nitrate solution wa s added to the aqueous laye r, and a mixture of two precipitates was obtained. (i) Identify the two precipitates formed. …………………………………………………………………………………………… ……………………………………………………………………………………………

 VJC 2011 9647/02/PRELIM/11 [Turn over   6 (ii) The iodine collected in the organic layer was titrated against 0.500 mol dm 3 sodium thiosulfate. 14.90 cm 3 of titrant was required to discharge the blue-black colour of the starch indictor. Calculate the value of m. (iii) The two precipitates can be se parated by addition of concentrated aqueous ammonia, followed by filtrati on. Describe what you expect to observe and explain the chemical principles behind this method. ………………………………………………………………………………..………… ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………..………… ………………………………………………………………………………………….. ………………………………………………………………………………..……........ [7]

 VJC 2011 9647/02/PRELIM/11 [Turn over   7 (c) 0.500 g of a Group II iodate(V) salt, M( IO3)2, was heated and decomposed to give a white solid, a purple gas, and a colourless gas that rekindles a glowing splint. (i) Identify the 3 dec omposition products. …………………………………………………………………………………………… …………………………………………………………………………………………… (ii) Write a balanced equation for the decom position reaction, including state symbols. …………………………………………………………………………………………… (iii) Given that 0.0532 g of the white so lid was collected, calculate the relative atomic mass of the metal, and hence deduce its identity. [4] (d) Predict how the thermal dec omposition of barium iodate( V) differs from that of M(IO3)2. Explain your reasoning. ………………………………………………………………………………..……................. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………..……………….. ………………………………………………………………………………………………… ………………………………………………………………………………..……………. [3]  [Total: 16]

 VJC 2011 9647/02/PRELIM/11 [Turn over   8 3 The two most abundant atmospheric gases react to a small extent at 298 K in the presence of a catalyst to achieve dynamic equilibrium as shown: N2(g) + O2(g) 2NO(g) Kp = 0.30 (a) Explain the term dynamic equilibrium. ……………………………………………………………………………………..….………. ……………………………………………………………………………………………... [1] (b) Atmospheric oxygen and nitrogen, each at a partial pressure of 0.780 atm, are put into a 1 dm 3 evacuated flask at 298 K with a catalyst and equilibrium is established after 30 minutes. Calculat e the equilibrium partial pressure for each of the three components at 298 K. [3] (c) What is the total pressure in the container at equilibrium? [1] (d) Find K c for this reaction at 298 K. [1]

 VJC 2011 9647/02/PRELIM/11 [Turn over   9 (e) On the grid below, sketch pressu re versus time curves for N 2 and NO under the conditions as described in (b) at 298 K from