AJC H2 Chem 2012 Prelim P2 QP

NAME:______________________________ PDG:__________ Register No: _____ ANDERSON JUNIOR COLLEGE Preliminary Examinations 2012 CHEMISTRY 9647/02 Higher 2 13 September 2012 Paper 2 Structured Questions 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, PDG and register number on all the work you hand in. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer ALL questions. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 2 3 4 5 Total This document consists of 20 printed pages. AJC Prelim 2012 9647/02/H2 [Turn over

2 AJC Prelim 2012 9647/02/H2 1 Planning (P) Suppose you are given a solution containing Zn2+, Al3+, Cl– and I– ions. You are also provided with the following: reagents apparatus · NaOH(aq), · NH3(aq), · HNO3(aq), · HCl(aq), · AgNO3(aq) and · distilled water · test tubes, · filter funnel and · filter paper (a) (i) Name the reagent, from the list provided, that can be used to convert both th e Cl– and I– ions to precipitates. ……………………………………………………………………………………………………... (ii) Name another reagent, from the list provided, that can be used to dissolve one of the precipitates formed in (a)(i). ………………………………………………………………………………… …………………... [2] (b) Using the reagents you have identified in (a), you are to devise a sequence of steps, by which the halides in the mixture could be separated such that each halide is present in a separate precipitate. In your plan, you need to include details on the reagents you will use, expected observations and state the location of each anion (i.e. in a solution or precipitate) after each step. You may present your answer in the form of a table or flow chart. [2]

3 AJC Prelim 2012 9647/02/H2 [Turn over (c) A small amount of dilute nitric acid is usually added before the addition of the reagent you have chosen in (a)(i). Suggest a reason why this is done. ……………………………………………………………………………………………………………. ……………………………………………………………………………… ……………………………. [1] (d) One of the cations present in the above mixture, Zn2+ or Al3+, can be removed as a precipitate, on reaction with excess of either NaOH(aq) or NH3(aq). Identify the reagent to be added in excess and which cation, Zn 2+ or Al3+, can be removed as a precipitate. Explain your answer using relevant equations. Reagent to be added in excess ………………………………………………………………………. Cation precipitated ……………………………………………………………………………………... Explanation…………………………………………………………………… …………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. [2] You are provided with 3 unlabeled bottles each containing one of the following organic halogen derivatives. · bromobenzene, C6H5Br · (bromomethyl)benzene, C6H5CH2Br · ethanoyl bromide, CH3COBr You are also provided with the following: reagents apparatus · NaOH(aq), · NH3(aq), · HNO3(aq), · HCl(aq), · AgNO3(aq) and · distilled water · test tubes, · filter funnel, · filter paper and · Bunsen burner (e) Outline a logical sequence of chemical tests that would enable you to identify each of the compounds. You need to describe in a clear, stepwise manner, the tests used to identify each compound. For each test, you need to include · details on the reagents and conditions you will use, · their quantities and · the expected observations for each compound tested in that particular step. You may present your answer in the form of a table or flow chart.

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5 AJC Prelim 2012 9647/02/H2 [Turn over 2 (a) (i) The value of pV is plotted against p for the following three gases, where p is the pressure and V is the volume of the gas. 1 mol CO2 at 298 K 1 mol CO2 at 473 K 1 mol SO2 at 298 K Given that graph A represents the graph for 1 mol of CO 2 at 298 K, identify and explain what graphs B and C represent. Graph B: …………………………….. Graph C: …………………………….. ……………………………………………………………………………………………………... ……………………………………………………………… ……………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... pV p Graph A: 1 mol of CO2 at 298 K Graph B Graph C

6 The van der Waals ’ equation as shown below is often used to account for the disc repancies between experimental and theoretical behaviour of real gases. (p + 2 2 V a n)(V – nb) = nRT p is the pressure, V the volume, T the temperature, n the amount of substance (in mol), and R the gas constant. The van der Waals’ constants a and b are characteristic of the substance and are independent of temperature. (ii) Given that the van der Waals ’ constants a and b for SO 2 is 0.687 Pa m 6 mol–2 and 5.68 x 10–5 m3 mol–1 respectively, calculate the actual pressure exerted by 1 mol of SO 2 in a 0.5 dm3 container at 25 oC. (iii) Calculate the pressure exerted by SO 2 as described in (a)(ii) if it obeys the ideal gas law. (iv) Suggest a reason for the discrepancy in the pressures obtained in (a)(ii) and (a)(iii). ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... [6]

7 AJC Prelim 2012 9647/02/H2 [Turn over (b) A wide range of sulfur oxoanions exist and many of them are widely used in laboratory synthesis. Four of such oxoanions have two sulfur (S) atoms. The average oxidation number of S and number of oxygen in the anions are shown in the table below. oxoanion average oxidation number of S number of oxygen atoms D +2 3 E +3 4 F x 6 G +6 y All four sulfur oxoanions have a negative charge of 2–. Only D has one central atom. In D, E and F only, · t he sulfur atoms are bonded directly to each other and · no oxygen atom is attached to another oxygen atom. (i) Suggest a value for x and y in the table. Value of x: ……………........ Value of y: ……………….... (ii) Suggest the structural formulae of D and E. Structural formula of D Structural formula of E (iii) Using VSEPR theory, suggest the shape of oxoanion E with respect to each S atom. ……………………………………………………………………………………………………...

8 (iv) Oxoanion G is a powerful oxidising agent. G + 2e 2SO42– Eo = +2.01 V Using the above data and in formation given in the question, draw the dot– and–cross diagram of oxoanion G. [5] (c) Thionyl halides su ch as SOC l2 are commonly used in the halogenation of organic compounds. The reaction also results in the production of hydrogen halide vapour. The following sketch shows the trend of vapour pressure exerted by the different thionyl halides at a given temperature. (i) Explain the above trend in terms of structure of, and bonding in, each of these thionyl halides. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………..