RVHS H2 CHEM P2 QP Prelim

River Valley High School 9647/02/PRELIM II/16 [Turn over 2016 Preliminary Examination II RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION II CANDIDATE NAME CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9647/02 Paper 2 Structured Questions 13 September 2016 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class, centre number and index number on all the work you hand in. Write in dark blue or black pen on both sides of paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions in the space provided. A Data Booklet is provided. Do NOT write anything on it. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Paper 2 Question Number 1 2 3 4 5 6 Total (Paper 2) Marks 12 13 8 9 16 14 72 Paper 1 40 Paper 3 80 Total 192 This document consists of 18 printed pages and 2 blank pages.

2 River Valley High School 9647/02/PRELIM II/16 2016 Preliminary Examination II 1 Planning (P) Salicylic acid is known for its ability to ease aches and pains as well as reduce fevers. Its analgesic and anti-inflammatory properties makes it one of the most important medications needed in a basic health system, placing it on the World Health Organisation Model List of Essential Medicines. It can be synthesised via the alkaline hydrolysis of methyl salicyla te, followed by acidification. methyl salicylate salicylic acid (Mr = 152) (Mr = 138) Methyl salicylate is a liquid with a density of 1.174 g cm3. Aqueous sodium hydroxide used for the hydrolysis has a concentration of 6.0 mol dm3. Like most organic reactions, the yiel d of this reaction is less than 100%. Using the procedure described below, a typical yield of pure salicylic acid is 60%. Methyl salicylate is mixed with aqueous sodium hydroxide in a molar ratio of 1:2. The reaction is heated under reflux conditions for around 30 minutes to form a di-sodium salicylate salt. When the reaction mixture has cooled down, concentrated hydrochloric acid is added until in excess to cause the crude salicylic acid to precipitate. This process is highly exothermic. The crude salicylic acid is then purified by recrystallisation from water. (a) Using the information given above: (i) write a balanced equation for the formation of the di -sodium salicylate salt; [1]

3 River Valley High School 9647/02/PRELIM II/16 [Turn over 2016 Preliminary Examination II (ii) calculate the volumes of methyl salicylate and aqueous sodium hydroxide you would use to prepare 10 g of pure salicylic acid, showing your working. [2] (b) Write a plan for the preparation of 10 g of pure salicylic acid. In your plan, you should:  draw a diagram of the assembled apparatus you would use when heating the reaction mixture;  give a full description of the procedures, including the capacities of the apparatus involved, you would use to prepar e and purify the salicylic acid;  explain how you would minimise a potential safety hazard.

4 River Valley High School 9647/02/PRELIM II/16 2016 Preliminary Examination II …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ……………………………………………………………………………………………………

5 River Valley High School 9647/02/PRELIM II/16 [Turn over 2016 Preliminary Examination II …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… [9] [Total: 12]

6 River Valley High School 9647/02/PRELIM II/16 2016 Preliminary Examination II 2 Sodium azide is a chemical found in car safety airbags. When the car undergoes a head-on collision, a series of chemical reactions occur in the gas generator chamber. The first reaction produces nitrogen gas to fill the airbag. The equation for the reaction is shown below: NaN3(s)  Na(s) + 2 3 N2(g) H < 0 (a) The volume of a fully inflated airbag is 60 dm3. Calculate the mass of NaN 3 needed to fill such an airbag to an internal pressure of 150 kPa at 300 °C. [2] (b) (i) Given that Sr = S(products)  S(reactants) and the following information, calculate S for the above reaction. Molar entropy of NaN3(s) 70.5 J mol1 K1 Molar entropy of Na(s) 51.3 J mol1 K1 Molar entropy of N2(g) 191.6 J mol1 K1 [1] (ii) Explain why the reaction is feasible at all temperatures. …………………………………………………………………………… …………………………………………………………………………… [1]

7 River Valley High School 9647/02/PRELIM II/16 [Turn over 2016 Preliminary Examination II (iii) Suggest why the reaction in fact occurs only at temperatures above 300 °C. …………………………………………………………………………… …………………………………………………………………………… [1] (c) Sodium metal formed in the above reaction is very reactive and is made to react with potassium nitrate present in the airbag, forming sodium oxide as one of the products. (i) Explain what is meant by the lattice energy of sodium oxide. …………………………………………………………………………… …………………………………………………………………………… [1] (ii) Using the information given below and relevant information from the Data Booklet, construct an energy level diagram to calculate the lattice energy of sodium oxide. Enthalpy change of formation of sodium oxide = 416 kJ mol1 Enthalpy change of atomisation of sodium = +107 kJ mol1 Sum of 1st and 2nd electron affinity of oxygen = +702 kJ mol1 [3]

8 River Valley High School 9647/02/PRELIM II/16 2016 Preliminary Examination II (iii) Given that the 1 st electron affinity of oxygen is 142 kJ mol 1, calculate the 2 nd electron affinity of oxygen and explain the significance of its sign. ……………………………………………