TJC Prelim P2 Qn

1 2017 TJC H2 Chemistry Preliminary Exam [Turn over s CANDIDATE NAME CIVICS GROUP / CENTER NUMBER S INDEX NUMBER CHEMISTRY 9729/02 Paper 2 Structured Questions 11 September 2017 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Civics Group, centre number, index number and name on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. 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. This document consists of 18 printed pages For Examiner’s Use 1 / 22 2 / 15 3 / 21 4 / 8 5 / 9 Paper 1 / 30 Paper 3 / 80 Total PRELIMINARY EXAMINATIONS HIGHER 2

2 2017 TJC H2 Chemistry Preliminary Exam [Turn over Answer all the questions 1 Silver chloride is an important photosensitive inorganic material widely used in photographic applications. It is industrially produced by mixing solutions of silver nitrate and sodium chloride. Ag+(aq) + Cl-(aq) AgCl(s) ∆Hppto = -65.7 kJ mol-1, ∆Sppto = -34.3 J mol-1 K-1 (a) (i) Suggest whether a lower or higher temperature should be used to increase the yield of silver chloride. Explain your answer. [2] (ii) Calculate ∆Go of the precipitation of AgCl. [1] (iii) In view of your answer in (a)(ii), comment on the solubility of silver chloride in water. [1]

3 2017 TJC H2 Chemistry Preliminary Exam [Turn over (b) (i) Lattice energies are not measured directly. The value calculated using Hess’ Law and the Born-Haber cycle is the experimental lattice energy. Using ∆Hppto of AgCl(s), the following data and relevant data from the Data Booklet, calculate the experimental lattice energy of AgCl(s). standard enthalpy change of formation of Ag+(aq) +106 kJ mol–1 standard enthalpy change of formation of Cl-(aq) –167 kJ mol–1 standard enthalpy change of atomisation of Ag(s) +285 kJ mol–1 first electron affinity of chlorine –349 kJ mol–1 [3]

4 2017 TJC H2 Chemistry Preliminary Exam [Turn over The theoretical value of lattice energies are calculated using the distances between the cations and anions in the crystal structure, and the charge on each ion. The table below shows the numerical values of experimental and theoretical lattice energies for sodium chloride and silver fluoride. compound experimental value/ kJ mol-1 theoretical value/ kJ mol-1 NaCl -771 -766 AgF -967 -953 (ii) It can be s een that the experimental and theoretical values for sodium chloride and silver fluoride are quite similar. However, the theoretical value for the silver chloride is significantly less exothermic than the experimental value. Suggest a reason for this. [1] (c) Explain, with the aid of equations, why silver chloride is soluble in aqueous ammonia while silver iodide does not dissolve in aqueous ammonia. [3]

5 2017 TJC H2 Chemistry Preliminary Exam [Turn over (d) (i) Most of the energy our bodies need comes from carbohydrates and fat. Starch is broken down into glucose,C6H12O6. Glucose exist mainly in cyclic forms with a small percentage in open chains. open-chain cyclic State what you would observe when glucose is added to an alkaline solution of ammoniacal silver(I) nitrate. [1] Glucose is transported to the cells to react with oxygen via a series of steps to form carbon dioxide, water and energy. (ii) Write a balanced equation for the reaction of glucose with oxygen. [1] (iii) Using data from the Data Booklet, calculate the amount of energy released per mole of glucose using the cyclic structure. [2]

6 2017 TJC H2 Chemistry Preliminary Exam [Turn over (iv) The literature value for the amount of energy released per mole of glucose is – 2800 kJ. Apart from bond energies are average values, suggest another reason for the difference between this value and that calculated in (d)(iii). [1] Like carbohydrates, fats are metabolised into carbon dioxide and water and when subjected to combustion in a bomb calorimeter. The reaction of tristearin, C57H110O6, a typical fat is as follows: C57H110O6 + 163 2 O2 → 57 CO2 + 55 H2O ∆Ho = -37760 kJ mol-1 The fuel value is the energy when one gram of the material undergoes combustion. The table below shows the fuel value of carbohydrates and protein and the food label of a cup noodle: Fuel value / kJ g-1 Carbohydrate 17 Fat (Tristearin) To be calculated Protein 17 (v) Determine the fuel value of tristearin and hence deduce if tristearin or carbohydrate is a better source of energy. (Mr of tristearin = 890) [2]

7 2017 TJC H2 Chemistry Preliminary Exam [Turn over (vi) During reading or watching television, the average adult uses about 7 kJ/min. How many minutes of such activity can be sustained by the energy supplied by a serving of cup noodle (considering only the total fat, total carbohydrate and total protein content)? [1] (e) In the body, glucose is also converted to energy via alcoholic fermentation. This process has been used in making beer and the side products such as esters contribute greatly to the taste and aroma of the beer. Ethyl acetate can be formed as follows CH3CO2H + CH3CH2OH CH3CO2CH2CH3 + H2O 1.51 mol of CH3CO2H and 1.66 mol of CH3CH2OH was allowed to reach equilibrium in a 100 cm 3 solution. 10 cm 3 of the equilibrium mixture was extracted and large amounts of cold water was added to quench the reaction. The mixture was then titrated with 22.40 cm3 of 2 mol dm-3 NaOH. Calculate the Kc for the formation of ethyl acetate. [3] [Total: 22]

8 2017 TJC H2 Chemistry Preliminary Exam [Turn over 2 (a) In 1887, the Swedish scientist Svante Arrhenius postulated that acids and bases dissociate in water to form hydrogen ions, H+, and hydroxide ions, OH−, respectively.