NJC H2 Chem 2012 Prelim P3 QP

CANDIDATE NAME SUBJECT CLASS NATIONAL JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Higher 2 REGISTRATION NUMBER CHEMISTRY 9647/03 Paper 3 Free response Tues 18 Sep 2012 2 hours READ THESE INSTRUCTIONS FIRST Answer any four questions. Start your answer to each question on a fresh piece of paper. 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 the end of the examination, fasten all your work securely behind the cover page. This paper consists of 13 printed pages including 1 blank page.

NJC/H2 Chem/03/2012 [Turn over 2 Answer any four questions. 1 (a) The graph below shows the variation of pV versus p for NH 3, which exists as a gas under normal room conditions. Explain the shape of the graph, commenting on the behaviour of NH 3 gas as an ideal gas at A, B, C and D. [3] (b) Ammonia is manufactured by the Haber Process, using gaseous nitrogen and hydrogen. 3H 2(g) + N2(g) 2NH3(g) DH = –92.4 kJ mol–1 In an experiment starting with a 3:1 ratio of H 2 and N2 mixture at 400 oC and a constant total pressure of 200 atm in the presence of iron catalyst, the equilibrium mixture was found to contain 36.3 % by volume of ammonia. (i) Justify the conditions of temperature and pressure used. (ii) Write an expression for K p of this reaction. (iii) Calculate the partial pressures of each of these three gases at equilibrium, and hence calculate K p at this temperature, stating its units. [6] (c) Hydrazine, NH 2NH2 , is a flammable liquid with ammonia-like odour. It has basic chemical properties like ammonia. Compound NH2NH2 NH3 Kb / mol dm–3 1.3 x 10–6 1.8 x 10–5 Explain the difference in the K b values of these two compounds. [2] A B C D Ideal gas NH3 pV / J p / atm

NJC/H2 Chem/03/2012 [Turn over 3 1 (d) Hydrazine is miscible with water but immiscible with trichloromethane. (i) Explain, in terms of bonding, and with appropriate diagrams to illustrate, the difference in the miscibilities of hydrazine with the two stated solvents. (ii) Hydrazine hydrate, made from hydrazine, takes part in the following reaction: NH2NH2.H2O + IO3– + 2H+ + Cl– ® N2 + ICl + 4H2O Calculate the change in the oxidation states of the species oxidised. [4] (e) Hydrazines are part of many organic syntheses and undergo condensation reactions with carbonyl compounds. Below is a scheme showing some reactions of phenylethanone, which includes the reaction mentioned. COCH3 H2 /Ni T, P Compound B Reagent X NH2NH2 Compound A Compound C phenylethanone sodium benzoate (i) Draw the structural formulae of Compounds E, F and G. (ii) State what Reagent X is, and give the conditions under which the reaction will take place. [4] (f) Hydrazine reacts in a similar way with an isomer of phenylethanone, H. H is also a monosubstituted benzene like phenylethanone. Suggest the identity of H. [1] [Total: 20] Compound E Compound G sodium benzoate + Compound F high temp and pressure phenylethanone Reagent X

NJC/H2 Chem/03/2012 [Turn over 4 2 The Group II element, barium, was first isolated by Sir Humphry Davy, a British chemist and inventor in the nineteenth century. Besides being used widely in pyrotechnics, barium is also used in the production of hydrogen peroxide, a colourless liquid with a boiling point of 150 ºC. Hydrogen peroxide was originally produced commercially in a two-stage process. In the first stage, barium was heated in air to form barium peroxide. In the second stage, barium peroxide was added to aqueous nitric acid. The equations for the reactions are shown below. Stage 1: Ba(s) + O 2(g) ® BaO2(s) Stage 2: BaO2(s) + 2HNO3(aq) ® H2O2(aq) + Ba(NO3)2(aq) (a) (i) Suggest one method of separating hydrogen peroxide from the reaction mixture in Stage 2. (ii) Suggest one reason why nitric acid was eventually replaced by sulfuric acid in Stage 2 to lower the cost of this commercial production. (iii) Draw the dot-and-cross diagram for barium peroxide. [3] (b) (i) Write an equation for the reaction of barium with water. (ii) Would the reaction in (i) occur more or less vigorously than that for magnesium? Justify your answer by quoting relevant data from the Data Booklet. [3] (c) Although Group II elements can form many compounds, the standard enthalpy of formation of solid barium chloride cannot be obtained directly. (i) Define the term standard enthalpy of formation of barium chloride. (ii) Given the standard enthalpy change of solution of barium chloride is -13.2 kJ mol -1, write a thermochemical equation to represent the standard enthalpy change of solution of barium chloride.

NJC/H2 Chem/03/2012 [Turn over 5 2 (c) (iii) Using the information from (ii) and the following data: draw an appropriate energy cycle and use it to calculate the enthalpy change of formation of solid barium chloride. (iv) Use the following entropy data and your answer to (iii), BaC l2 (s) Ba(s) Cl2(g) Sθ /J K-1 mol-1 124 63 223 calculate the lowest temperature at which the following reaction becomes feasible. BaC l2(s) ® Ba(s) + Cl2(g) [9] (d) Catalytic poisoning is normally undesirable as it results in a loss of the usefulness of expensive metals like platinum and palladium. However, poisoning of a catalyst can be used to enhance selectivities of some reactions. An example of such practice is seen in the Rosenmund reduction where carbonyl compounds are produced. The palladium catalyst required for this reduction reaction is poisoned with barium sulfate. The scheme below shows a 4– step synthesis of compound G which has the molecular formula C 3H9ON. One of the steps involves the Rosenmund reduction. CH3COOH D E F Give the structural formulae of compounds D – G and the reagent(s) and conditions required for Step (i). [5] [Total: 20] Reaction DH θ / kJ mol-1 Ba(OH)2(aq) + 2HCl(aq) ® BaCl2(aq) + 2H2O(l) -114.4 H2(g) + ½ O2(g) ® H2O(l) -285.9 ½ H2(g) + ½ Cl2(g) ® HCl(g) -92.3 HCl(g) + aq ® HCl(aq) -71.9 Ba(s) + O2(g) + H2(g) + aq ® Ba(OH)2(aq) -1002 H2 /Pd BaSO4 Step (i) SOCl2 HCN G C3H9ON

NJC/H2 Chem/03/2012 [Turn over 6 3 (a) In the Clemmensen reaction, zinc is used, along with hydrochloric acid, for the reduction of a carbonyl compound into an alkane. C O R R' Zn, HCl heat R C H H R' Clemmensen reaction W and X are carbonyl compounds which undergo Clemmensen reaction to form the same alkane, Y. W is an optically active compound but X and Y are not. Only W forms a silver mirror with Tollen’s reagent. 0.3 mol of Y burns in excess oxygen to produce 33.6 dm 3 of CO2 at standard temperature and pressure. Calculate the number of moles of CO2 produced, and hence deduce the possible structures of W, X and Y. [4] (b) Compound J has molecular formula of C4H7Cl and exhibits the following