MI Prelim 9647 P2

Class Adm No Candidate Name: This question paper consists of 17 printed pages and 1 blank page. 2017 Preliminary Examination II Pre-University 3 H2 CHEMISTRY 9647/02 Paper 2 Structured Questions 12th Sept 2017 2 hours Candidates answer on the Question paper. Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number 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. 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. Question 1 2 3 4 5 Total Marks 12 14 15 11 20 72

2 1 Planning (P) Hydrogen peroxide undergoes a redox reaction with acidified KMnO4 as follows: 2MnO4-(aq) + 5H2O2(aq) + 6H+(aq) → 2Mn2+(aq) + 5O2(aq) + 8H2O(l) By itself, hydrogen peroxide decomposes slowly in accordance to the following equation: 2H2O2(aq) → 2H2O(l) + O2(g) It is found that the decomposition reaction is first order with respect to H 2O2. The reaction can be accelerated by using solid manganese(IV) oxide as the catalyst. (a) Write the rate equation for the decomposition of hydrogen peroxide. ………………………………………………………………………………………………………… [1] (b) Using the information given, you are required to write a plan to determine the rate constant for the decomposition of hydrogen peroxide using the continuous titration method. You may also assume that you are provided with:  250 cm3 of 0.0100 mol dm-3 acidified KMnO4;  250 cm3 of 0.0250 mol dm-3 H2O2 solution;  Solid manganese(IV) oxide;  25.0 cm3 pipette;  Stopwatch;  the apparatus normally found in a school or college laboratory. Your plan should include:  practical details of how you would  determine if dilution of the reaction mixture is needed for titration against H2O2;  ensure the reaction is complete;  carry out the titration;  a sketch of the graph you would expect to obtain;  brief, but specific, details of how the results would then be used to obtain  the initial rate of reaction of decomposition in mol dm-3 min-1,  the rate constant for the reaction

3 [Turn over ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. …………………………………………………………………………………………………………….

4 ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………….. [11] [Total: 12]

5 [Turn over 2 Hydrogen iodide can undergo decomposition to give a mixture of hydrogen gas and iodine gas. 2HI(g) ⇌ H2(g) + I2(g) ∆H = +12.0 kJ mol-1 (a) State Le Chatelier’s Principle. ……………………………………………………………………………………………………………. ………………………………………………………………………………………………………… [1] (b) Predict and explain the effect of the following changes on the position of the above equilibrium, if any. (i) Increasing the temperature ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. …………………………………………………………………………………………………… [2] (ii) Reducing the pressure ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. …………………………………………………………………………………………………… [1] (iii) Addition of catalyst ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. …………………………………………………………………………………………………… [1]

6 (c) When 1.4 mol of hydrogen iodide is hea ted in a closed vessel at 550 K, the total pressure at equilibrium was 6 atm. Given that the mole ratio of hydrogen iodide to iodine gas at equilibrium is 9:4, calculate the equilibrium constant, Kp, at 550 K. [3] (d) Hydrogen chloride and hydrogen bromide also undergoes a similar decomposition to give hydrogen gas and its respective halogens. Describe the trend in the volatility and colours of the halogens. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………. [3]

7 [Turn over (e) It was observed that a beam of protons gives an angle of 27in the following electric field. Indicate on the diagram below how a beam of protons, 127I- and 23Na+ ions, travelling at the same speed, behave in the same electric field. Calculate the respective angles of deflection. Working: [3] [Total: 14] Source - +

8 3 In 1933, chemists in Britain discovered that when ethene was subjected to high pressures in the presence of a trace amount of oxygen or organic peroxide, it produced low -density poly(ethene) (LDPE). The radical mechanism using organic peroxides is shown below. Using triethylaluminium, also known as Ziegler-Natta catalyst, developed by Karl Ziegler and Giulio Natta in 1953, ethene can be polymerised at much lower pressures to produce high -density poly(ethene) (HDPE). In the first step, triethylaluminium can accept the pair of  electrons of ethene to form a carbocation which is very similar to that found in the usual electrophilic addition reactions. This carbocation then undergoes an addition reaction with another ethene molecule. Eventually, long chains of ethene units fo