PJC H2 CHEM P3

PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION HIGHER 2 CANDIDATE NAME CT INDEX GROUP NUMBER CHEMISTRY 9647/03 Paper 3 Free Response 24 September 2014 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Graph Paper Data Booklet Cover Page READ THESE INSTRUCTIONS FIRST Write your name, CT group and index number on all work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough workings. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At then end of the examination, fasten all your work securely together. This document consists of 12 printed pages. 1 3

© PJC 2014 9647/03/JC2 Prelim/2014 2 Answer any four questions. 1 (a) The graph below shows the second and th ird ionisation energies for the first d-block elements scandium to zinc. Ionisation energy / kJ mol 1 By writing relevant electronic configurations, explain why (i) the second ionisation energy of ch romium is higher than that of manganese. (ii) the third ionisation energy of iron is lower than that of manganese. [4] (b) An aqueous solution contains a mixture of iron(III) and zinc ions. (i) Draw a diagram to show the bonding in the hexaaquairon(III) complex ion. (ii) Describe, in a sequence of steps, how you would separate the two cations so that they are obtained as Fe 3+(aq) and Zn2+(aq). Write equations for all the reactions that iron(III) ion and its compound have undergone. You are only provided with HNO3(aq) and NaOH(aq). [5] (c) An aqueous iron( III) solution can be used as a homogeneous catalyst for the reaction between iodide ions and peroxodisulfate ions, S2O8 2. By considering relevant Eo values from the Data Booklet, describe and explain the role of iron( III) ions in the reaction between I and S 2O8 2. Write equations and calculate the Eo cell for the reactions that occur. [4] 2nd IE 3rd IE

© PJC 2014 9647/03/JC2 Prelim/2014 3 (d) The kinetics of the uncatalysed reaction between peroxodisulfate ions and iodide ions can be investigated experimentally. S 2O8 2(aq) + 2I(aq) → 2SO4 2(aq) + I2(aq) To find the rate equation: rate = k[S 2O8 2(aq)]a[I(aq)]b for this reaction, a continuous method with sampling is used. In an experiment, 50.0 cm 3 of 0.200 mol dm 3 of aqueous sodium iodide was mixed with 50.0 cm 3 of 2.00 mol dm 3 aqueous sodium pero xodisulfate. At various time intervals, 10.0 cm 3 of the reaction mixt ure was withdrawn and quenched with 50 cm 3 of ice-cold water. The re sultant mixture was titrated against 0.0250 mol dm 3 aqueous potassium thiosulf ate, using starch as an indicator. The reaction between thiosulfate and iodine is as follows: 2S 2O3 2 + I2 → S4O6 2 + 2I The results are shown below: Time / min 0 2 4 6 12 16 Volume of K2S2O3 (aq) / cm3 0 9.50 17.00 22.50 32.25 35.50 (i) Show that 40.00 cm 3 of standard aqueous pota ssium thiosulfate is required to react with 10.0 cm 3 of the reaction mixtur e when the reaction between peroxodisulfate and iodide ions is complete. (ii) By drawing a suitable graph, use it to show that the reaction is first order with respect to iodide ions. (iii) The order of reaction with respect to per oxodisulfate ions is reported to be one. You are required to conduct a second exper iment using the same experimental procedures to confirm the order of reaction. Suggest suitable concentrations of aqueous sodium iodide and sodium peroxodisulfate to be used and explain how the data obtained could be used to confirm the order of reaction. [7] [Total: 20]

© PJC 2014 9647/03/JC2 Prelim/2014 4 2 The halogens are an important class of inorganic elements that forms a large variety of halogen-containing products, many of which are useful to us. Three members of the series, namely chlorine, bromine and iodine, were discovered in the 19 th century by Humphry Davy, Antoine-Jérôme Balard and Bernard Courtois respectively. (a) A student carried out a series of redox reactions on three unknown halogens, R2, S2 and T2, and their respective halides. Aqueous solutions of R2 and S2 are brown in colour, while an aqueous solution of T2 is colourless. For each experiment, an unknown halogen was added to a solution containing an unknown halide. This was fo llowed by the addition of tetrachloromethane to the resultant solution. The following table shows the result s and observations obtained from the experiments. Experiment Number Reagent 1 Reagent 2 Colour of the organic layer after adding and shaking with tetrachloromethane 1 R2(aq) S(aq) violet 2 T2(aq) R(aq) violet 3 S2(aq) T(aq) red-brown (i) Explain the role of tetrachloromethane in the series of experiments. (ii) Deduce the identities of R2, S2 and T2. Explain your reasons clearly. [6] (b) To determine the standard redox potential of the Br2|Br system, a student set up the apparatus as shown in the diagram below. However, she accidentally spilled a few drops of aqueous silver nitrate to the Br 2|Br half-cell. Explain how the Ecell of the system would be affe cted. State w hat would be observed and write an equation for any reaction that occurred. [3] V platinum electrode 1 mol dm3 H+(aq) salt bridge H2 gas at 25 oC, 1 atm 1 mol dm3 Br2 (aq) 1 mol dm3 Br(aq) platinum electrode

© PJC 2014 9647/03/JC2 Prelim/2014 5 (c) Halogens can function as ox idising agents, while thei r halides can function as reducing agents. Use the Data Booklet to predict what you would expect to observe when the following pairs of solutions are mixed. Write balanced equation for any reaction that occurs. (i) aqueous bromine and aqueous hydrogen peroxide (ii) aqueous sodium chloride and aqueous iron(III) nitrate [4] (d) (i) The following table shows the boiling points of three organic compounds. Organic Compound Boiling Point / oC CH3Cl 24 CH3CH2F 37 CH3CH2Cl 12 Explain the difference in boiling points between  CH 3Cl and CH3CH2Cl  CH 3Cl and CH3CH2F (ii) Ammonium hydrogen difluorid e is a colourless salt that is used as an etchant to allow different designs to be engraved onto glass. It contains one cation and one anion. It is form ed by the reaction between ammonia and hydrogen fluoride. I Write an equation for the format ion of ammonium hydrogen difluoride from ammonia and hydrogen fluoride. II Suggest the structure for the anion and state the types of bonding occurring within it. [7] [Total: 20]

© PJC 2014 9647/03/JC2 Prelim/2014 6 3 (a) Aluminium and phosphorus form the chlorides AlCl3 and PCl3. (i) When aqueous sodium carbonate is added to aqueous aluminium chloride, a colourless gas is liberat ed and a white precipitate is formed. Give an ionic equation for the reacti on and briefly account for the gas produced. PCl 3 reacts with water according to the following equation. PCl3 + 3H2O → H3PO3 + 3HCl In an experiment, 1.00 g of PC l3 was dissolved in water. The resulting solution was made up to 250 cm 3 in volumetric flask. 25.0 cm 3 of this solution is titrated with 0.200 mol dm3 of NaOH and required 18.20