ACJC H2 CHEM P2 Prelim

Index No. Name Form Class Tutorial Class Subject Tutor ANGLO-CHINESE JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Advanced Level CHEMISTRY 9746/02 Higher 2 Paper 2 Structured 24 August 2009 1 hour 30 minutes Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, index number, form class, tutori al class and subject tutor’s name on all the work you hand in. Write in dark blue or black pen. 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. A Data Booklet is provided. 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 together including the cover page. For Examiner's Use Question no. Marks 1 2 3 4 TOTAL This document consists of 11 printed pages. 9746/02/Prelim/09 ANGLO-CHINESE JUNIOR COLLEGE © ACJC 2009 Department of Chemistry [Turn over

2 1 Carbonyl fluoride, COF 2 (structure as shown below) exists as a toxic gas which reacts rapidly with water to evolve two different acidic gases. C O FF (a) (i) The reaction of carbonyl fluoride with water is found to proceed via the formation of an intermediate as shown: C OH HO F F State the reaction that has occurred to produce the above intermediate. [1] (ii) The above intermediate is found to dissociate rapidly to give two different acidic gases. One of the gases is carbon dioxide. State the identity of the other gas. [1] (iii) Using the above information, write a balanced equation of the reaction between carbonyl fluoride and water. [1] (b) An unknown amount of carbonyl fluoride was reacted with water (in excess). The two acidic gases released is then reacted with NaOH(aq). 25.00 cm 3 of 0.100 mol dm-3 of NaOH(aq) is required for complete neutralisation. (i) Calculate the number of moles of NaOH that has reacted. [1] © ACJC 2009 9746/02/Prelim/09 [Turn over

3 (ii) Calculate the number of moles of CO2 produced. [3] (iii) Using your answer in b(ii), calculate the volume of carbon dioxide in m 3 produced under the conditions of 30 C and 1 atm (assuming ideal gas behaviour). [1] (iv) Calculate the mass of carbonyl fluoride used. [1] (c) Carbonyl fluoride is found to dissociate to form CO 2 and CF4 as shown below: 2COF2(g) CO 2(g) + CF4(g) (i) Given that the Kc value of the above reaction at 1000 C is 2.00, calculate the number of moles of COF2 that remains undissociated at equilibrium when 0.500 mol of COF2 is placed in a 3.50 dm3 vessel at 1000 C. [4] © ACJC 2009 9746/02/Prelim/09 [Turn over

4 (ii) State and explain how the yield of CO2 will be affected when the total pressure in the vessel is increased. [2] [Total: 15] 2 (a) Group II metal, X reacts very slowly with cold water but vigorously with steam. Group II metal, Y readily reacts with cold water. Suggest the identity of X and Y, and give a reason for your choice. [2] (b) Give one property of magnesium oxide which makes it suitable for furnace lining. [1] (c) (i) SiO 2, also known as silica, is a hard glassy mineral found in rock and sand. Glass contains about 70% silica, as well as 15% Na 2O and 9% CaO. Na 2O and SiO 2 react to form sodium silicates which help glass to increase elasticity. Describe how separate samples of SiO 2, Na2O and CaO react with water and write equations where appropriate. Estimate the pH of the resulting mixtures. [5] © ACJC 2009 9746/02/Prelim/09 [Turn over

5 (ii) Hence, suggest a reason why CaO can be used to effectively remove SO 2 produced in power stations. [1] (d) The table below contains some data for the halogens. Element Atomic Number Atomic Radius /nm Ionic Radius /nm Boiling Point /K F 9 0.064 0.133 86 Cl 17 0.099 0.181 238 Br 35 0.111 0.196 332 I 53 0.130 0.219 456 Explain the following: (i) The boiling point of bromine is lower than that of iodine. [2] (ii) The anionic radius of chlorine is larger than its atomic radius. [2] (e) Identify the type of reaction that occurs when chlorine reacts with hot aqueous sodium hydroxide? Write an ionic equation and describe any observations made. [2] [Total: 15] © ACJC 2009 9746/02/Prelim/09 [Turn over

6 3 (a) In the separate experiments methane was reacted with halogens when irradiated with ultraviolet light. Experiment 1 Samples of methane gas and chlorine are mixed together. Experiment 2 Methane gas is bubbled into liquid bromine. (i) Write down the observations in Experiment 2. [2] (ii) The reaction of methane and halogens is said to occur by a ‘free radical mechanism’. Explain what is meant by a free radical. [1] (b) Samples of gases methane and chlorine are mixed together and irradiated with ultraviolet light. The reaction goes through two propagation steps with the respective heat of reactions and activations energies. Step ∆H / kJmol -1 E a / kJmol-1 Propagation Step 1 +4 17 Propagation Step 2 -109 4 (i) Briefly outline the mechanism of the two propagation steps. [2] © ACJC 2009 9746/02/Prelim/09 [Turn over

7 (ii) Using the information above, sketch the combined energy profile diagram for the two propagation steps of the chlorination of methane showing all relevant energy changes. Please specify the reactants, products and intermediates. [4] (iii) Which of the propagation steps is the rate determining step? Explain. [2] © ACJC 2009 9746/02/Prelim/09 [Turn over

8 (c) The following results were obtained when hydrolysis of chloromethane with aqueous potassium hydroxide was performed. Experiment Initial [CH 3Cl] / moldm-3 Initial [KOH] / moldm-3 Initial rate / moldm-3s-1 I 0.10 0.10 0.024 II 0.10 0.15 0.036 III 0.20 0.20 0.096 (i) Determine the order of reaction with respect to both CH 3Cl and KOH and hence write the rate equation. [3] (ii) Free radical substitution of methane with chlorine often leads to polychlorinated methane such as trichloromethane. What is the product obtained when hydrolysis of trichl oromethane with aqueous potassium hydroxide is performed? [1]