DHS H2 Chem 2013 Prelim P2 QP

__________________________________________________________________________________ This question paper consists of 18 printed pages and 0 blank page. © DHS 2013 [Turn over Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY 9647/02 Paper 2 Structured 19 September 2013 2 hours Additional Materials: Data Booklet INSTRUCTIONS TO CANDIDATES 1 Write your name, index number and class on this cover page. 2 Answer all questions. 3 Write your answers in the spaces provided on the question paper. 4 A Data Booklet is provided. 5 The number of marks is given in brackets [ ] at the end of each question or part question. 6 You may use a calculator. For Examiner’s Use 1 / 12 2 / 15 3 / 9 4 / 10 5 / 15 6 / 11 Total / [72] % 492

2 © DHS 2013 9647/02 [Turn over Answer all questions in the space provided. 1 Planning Solubility is defined as the mass of solid that will dissolve in and just saturate 100 g of solvent at a particular temperature. When potassium nitrate dissolves in water, the temperature of the solution decreases as the enthalpy change of solution is endothermic. You are to plan an experiment to investigate how the solubility of potassium nitrate varies with temperature. The units of solubility are grams per one hundred grams of water (g/100 g of water). (a) (i) Predict how the solubility of potassium nitrate will change if the solution temperature is increased. (ii) Display your prediction in the form of a sketch, labeling clearly the y–axis. 25 temperature / °C [3] For  Examiner’s  Use 493

3 © DHS 2013 9647/02 [Turn over (b) You are to design an experiment to test your prediction in (a). (i) Given that the solubility of potassium nitrate at 70 °C = 11.3 mol dm–3 Calculate the maximum mass of potassium nitrate that can be dissolved in 100 g of water at 70 °C. (ii) Describe how you would carry out the experiment. You should • include the apparatus used; • ensure a wide range of results suitable for analysis by graph; • decide on the amount of water and potassium nitrate to be used; and • describe how the temperature of the solution is to be maintained. You may also assume that standard laboratory apparatus are available. For  Examiner’s  Use  494

4 © DHS 2013 9647/02 [Turn over (iii) Draw a table with appropriate headings to show the data you would record when carrying out your experiments and the values you would calculate in order to construct a graph to support or reject your prediction in (a). The headings must include the appropriate units. [7] For  Examiner’s  Use  495

5 © DHS 2013 9647/02 [Turn over (c) Potassium nitrate is used as an excellent additive in fertilisers. It dissolves in water with an enthalpy change of solution of +34.9 kJ mol–1. It is given that the lattice energy of potassium nitrate is –687 kJ mol –1 and the enthalpy change of hydration of potassium ion is –322 kJ mol –1. With the aid of an energy level diagram, calculate the enthalpy change of hydration of nitrate ion. [2] [Total: 12] 2 The use of Data Booket is relevant to this question. The nitrates, carbonates and hydroxides of Group II elements can undergo thermal decomposition. The nitrates of lead and zinc can undergo thermal decomposition similar to calcium nitrate. The decomposition temperatures of the three nitrates are given in the table below. Compound Decomposit ion temperature / °C Lead(II) nitrate, Pb(NO3)2 290 Zinc nitrate, Zn(NO3)2 105 Calcium nitrate, Ca(NO3)2 132 (a) Explain the data above by quoting relevant values from the Data Booklet and using your knowledge and understanding of the trend in the decomposition temperature of the Group II nitrates. [3] For Examiner’s  Use  496

6 © DHS 2013 9647/02 [Turn over (b) The mineral hydromagnesite is a hydrated carbonate of magnesium, with the formula Mg x(CO3)y(OH)z.nH2O and a molar mass of 466 g mol –1. Group II carbonates and hydroxides decompose to give the same solid product. When 1.00 g of a pure sample of hydromagnesite was heated to constant mass, 0.378 g of carbon dioxide was given off. Steam was also produced. The remaining white solid from the above decomposition was completely dissolved in 50 cm 3 of a 1.0 mol dm –3 solution of hydrochloric acid. The resultant solution was transferred into a volumetric flask and diluted to 250 cm 3 with deionised water. A 25.0 cm 3 aliquot of this diluted solution required 28.50 cm 3 of a 0.10 mol dm –3 solution of sodium hydroxide for complete neutralisation. (i) Calculate the value of y. (ii) Calculate the value of x. For  Examiner’s  Use  497

7 © DHS 2013 9647/02 [Turn over (iii) Hence or otherwise, deduce the values of z and n. (iv) Using your answers from parts b(i) to (iii), write a balanced equation, with state symbols, for the thermal decomposition of hydromagnesite. [9] (c) A mixture of magnesium oxide, alumina (A l2O3) and silica (SiO 2) is usually used in the manufacture of refractory material. Suggest, with explanation and suitable equations, how magnesium oxide can be separated from a mixture containing these three oxides. [3] [Total: 15] For  Examiner’s  Use  498

8 © DHS 2013 9647/02 [Turn over 3 The data for some liquids are given below: Mr boiling point/ °C density / g cm −3 ethanol 46 79 0.79 cyclohexane 84 81 0.78 hexane 86 69 0.66 (a) (i) Suggest why the boiling point of cyclohexane differs from that of hexane. (ii) Suggest why the density of ethanol differs from that of hexane. [3] (b) Equal volumes of 1.0 mol samples of the following liquids were mixed and the following results were obtained in the following table. Mixture of liquids Heat change Hexane mixed with cyclohexane No heat absorbed or given out Hexane mixed with ethanol ? (i) Explain why there was no heat change on mixing hexane and cyclohexane. For  Examiner’s  Use  499

9 © DHS 2013 9647/02 [Turn over (ii) Predict, with reasoning, the heat change on mixing hexane and ethanol. [3] (c) (i) Write a balanced equation, for the complete combustion of ethanol, C2H6O. (ii) By using appropriate bond energy data from the Data Booklet , calculate the enthalpy change of combustion of ethanol. [3] [Total: 9] For  Examiner’s  Use  500

10 © DHS 2013 9647/02 [Turn over 4 (a) Chlorine forms an oxide Cl2O6 which exists as singly charged ions in the solid state. The oxidation states of chlorine are +5 and +7 in the cation and anion respectively. Suggest the formulae of the ions and draw the dot–and–cross diagram for the cation. [3] Formula of cation: Formula of anion: (b) When chlorine is bubbled through cold sodium hydroxide solution and acidified silver nitrate solution, only half of the chlorine that has dissolved is precipitated as silver chloride. When the sodium hydroxide is hot, up to five–sixth of the chlorine can be precipitated. Explain the observations, giving balanced equations where appropriate. [3] dot–and–cross diagram of cation: For Exa