2013 MI H1 Chemistry P2 Promos

Class Adm No Candidate Name: This question paper consists of 13 printed pages and 1 BLANK PAGE. [Turn over 2013 Promotional Examination II Pre-university 2 H1 CHEMISTRY 8872 / 02 Paper 2 Structured Questions 18 September 2013 (WEDNESDAY) Candidates answer Section A on the Question Paper. 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this booklet until you are told to do so. Write your name, index number and class on all the work you hand in. Write in dark blue or black pen on both sides of the writing paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluids. Section A Answer all questions. Section B Answer two questions on separate answer paper. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, arrange your answers in numerical order and fasten all your work securely together. FOR EXAMINER’S USE SECTION A Q1 / 9 Q2 / 11 Q3 / 10 Q4 / 10 SECTION B Q__ / 20 Q__ / 20 Total / 80

2 SECTION A Answer all questions in the space provided. For Examiner’s Use 1. (a) Draw a dot-and-cross diagram to illustrate the bonding in H 3S+ and predict its shape. [2] (b) The bond angle of H3O+ is larger compared to that of H3S+. Explain. ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ [2] (c) Acids dissociate in water to give H3O+. A solution of sulfuric acid was prepared by adding 500 cm 3 of water to a 25.0 cm 3 solution of 2.5 mol dm-3 of sulfuric acid. (i) Calculate the concentration of the sulfuric acid solution formed. (ii) Hence calculate the pH of the solution formed. [3]

3 [Turn over 1. (d) In a titration, a solution of aqueous NH 3 was titrated against the sulfuric acid solution prepared in (c). Predict if the pH at the equivalence point would be equal to, more than or less than 7. Give an equation to support your answer. For Examiner’s Use pH: ________ Equation: _________________________________________________________ [2 ] [Total: 9] 2. The term halogen, coined by a Swedish chemist Baron Jons Jakob Berzelius, refers to Group VII elements. (a) Bromine, a halogen, reacts with hot aqueous KOH according to the equation below. 3Br2(g) + 6KOH(aq) → 5KBr(aq) + KBrO3(aq) + 3H2O(l) (i) What are the oxidation states of bromine in the three bromine-containing compounds in the reaction? Br2: _____ KBr: _____ KBrO 3: _____ (ii) Hence state the type of reaction that has occurred. _________________________________________________ [2]

4 2. (b) The diagram below shows the second ionisation energy of eight consecutive elements, P to W, in the Periodic Table. Their atomic numbers lie between 3 and 20. For Examiner’s Use (i) Which element represents a halogen? _________________ (ii) Explain the general increasing trend in second ionisation energies from elements Q to V. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ (ii) Predict, with reasons, the trend of second ionisation energies down Group VII. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ [6]

5 [Turn over 2. (c) In an experiment, a sample of 80Br was vapourised and passed through an electric field. Analysis of the deflection occurring in the electric field revealed that a beam of 80Br¯ gave an angle of deflection of 1.05°. On the diagram below, sketch how beams of gaseous 19F¯ and gaseous 56Fe2+ will travel in the electric field. Indicate the angle of deflection clearly in your sketch. [3] For Examiner’s Use [Total: 11] Beam of particles + ¯

6 3. At room temperature, brown nitrogen dioxide and colourless dinitrogen tetraoxide are in dynamic equilibrium according to the following equation: 2NO2(g) N2O4(g) For Examiner’s Use (a) Predict, with reasoning, how the position of equilibrium might change if the pressure is decreased. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ [2] (b) The Lewis structure of N2O4 is shown below. N N O O O O Using bond energy data from the Data Booklet, calculate the enthalpy change for the reaction 2NO2(g) N2O4(g) [1] (c) Hence predict what would happen to the colour of the system when heat is applied to the equilibrium system. Explain your answer. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ [3]

7 [Turn over 3. (d) (i) The diagram below shows the Boltzmann di stribution curve for the reaction at 298K. On the same diagram sketch the distribution curve for the same reaction carried out at 278K. For Examiner’s Use (d) (ii) Explain how a lower temperature affects the rate of reaction. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ [4] [Total: 10] EA Fraction of molecules Energy

8 4. Propyl ethanoate is a colourless liquid which gives pears their characteristic odour. It is commonly used in fragrances and as a flavour additive. It can be synthesised from bromoethane in 4 steps: For Examiner’s Use (a) Suggest reagents and conditions for steps I, II, III and IV. step reagents and conditions I II III IV [4] (b) State the type of reaction for steps I and III. Step I: ______________________ Step III: ______________________ [2] (c) Ester W is an isomer of propyl ethanoate. Suggest a simple chemical test which would enable you to distinguish between ester W and propyl ethanoate. You should state the reagents and conditions for the test, and describe how each of the isomers behaves. Reagents and conditions: ______________________________________________ ___________________________________________________________________ Observations: _______________________________________________________ ___________________________________________________________________ [4] [Total: 10]

9 [Turn over SECTION B Answer two of the three questions in this section on separate answer paper. 5. Formaldehyde, HCHO, is a colourless and pungent gas. Formaldehyde-based materials are used in many industries. The textile industry, for example, uses formaldehyde-based resins to make crease-resistant fabrics. (a) In view of its toxicity, formalde