IJC 2008 H1 Chemistry Prelim II Paper2

INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATIONS 2 in preparation for General Certificate of Education Advanced Level Higher 1 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY Paper 2 Structured and Free Response Questions Section A: Structured Candidates answer Section A on the Question Paper Section B: Free Response Additional Materials: Writing Papers Graph Paper Data Booklet 8872/02 15 September 2008 2 hour READ THESE INSTRUCTIONS FIRST Write your index number, name and civics group on all the work you hand in. Write in dark blue or black pen. You may use pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. For Examiner’s Use Section A 1 10 2 12 3 10 4 8 Significant Figures Handwriting Total 40 Section A: Structured Questions (40m) Answer all questions in the space provided. Section B: Free Response Questions (40m) Answer two questions on separate writing papers. You are advised to show all working in calculations. You are reminded of the need for good English and clear presentation in your answers. You are reminded of the need for good handwriting. Your final answers should be in 3 significant figures. You may use a calculator. 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. This document consists of 15 printed pages and 1 blank page. [Turn overInnova Junior College

2 © INNOVA 2008 8872/02 [Turn over For Examiner’s Use Section A Answer ALL questions on the space provided 1. Hydrazine is a chemical compound with the formula N 2H4. It has an ammonia-like odour, and is derived from the same industrial chemistry processes that manufacture ammonia. However, hydrazine has physical properties that are more similar to those of water. Hydrazine is used as rocket fuel as it decomposes into ammonia and nitrogen gas. This reaction is extremely exothermic and thus very suitable as an efficient thruster propellant. (a) Draw the Lewis structure for the hydrazine molecule. State its shape and indicate the H–N–H bond angle. Shape: ………………………. [2] (b) Write a balanced equation to illustrate the decomposition of hydrazine. ……………………………………………………………………………....….....….... [1] (c) Suggest a reason why the decomposition reaction is highly exothermic. ……………………………………………………………………………....…..…....… [1] (d) Hydrazine is also commonly used as a strong reducing agent. It reacts according to the following equation: It was found that 25.0 cm 3 of 1.40 mol dm -3 hydrazine requires 35.0 cm 3 of 1.00 mol dm -3 of acidified KMnO 4 (aq) for reaction. Determine the final oxidation number of manganese in the product. [3]

3 © INNOVA 2008 8872/02 [Turn over For Examiner’s Use (e) Hydrazine (b.p. 114 oC) and ethene, C 2H4 (b.p. – 104 oC) have similar molecular masses but have very different boiling points. (i) Draw a diagram of N2H4 to illustrate the bonding in the compound. [1] (ii) Explain the difference in their boiling points in terms of structure and bonding. ……………………………………………………………………………....……….. ……………………………………………………………………………....……….. ……………………………………………………………………………....……….. ……………………………………………………………………………....……….. ……………………………………………………………………………....……….. [2] [Total: 10] 2 The use of the Data Booklet is relevant to this question. (a) The 68Ge isotope of the Group IV element germanium is medically useful because it undergoes a natural radioactive process to give a gallium isotope, 68Ga, which can be used to detect tumours. This transformation of germanium occurs when an electron enters the nucleus, changing a proton into a neutron. (i) State the number of protons and neutrons in the 68Ga isotope formed. Number of protons : …………………… Number of neutrons: …………………… [1]

4 © INNOVA 2008 8872/02 [Turn over For Examiner’s Use (ii) While undergoing radioactive decay, the isotope will give out an alpha particle, α which is the nucleus of helium atom. If the angle of deflection of the alpha particle, α, is 3o. I. Draw the path for which the alpha particle, will take when placed in an electric field shown below. –––––––– + + + + + + + + Source Neutrons [1] II. Give reasons and suggest the angle of deflection of the deuterium ion, 2 1 D+ . ……………………………………………………………………………....……….. ……………………………………………………………………………....………. [1] (b) Aluminium is by far the most abundant and important metal in earth’s crust. Aluminium reacts directly with non-metallic elements to form compounds such as aluminium oxide and aluminium chloride. (i) Write balanced equation(s) for the following reactions 1. Aluminium oxide with hot sodium hydroxide ……………………………………………………………………………....……….. ……………………………………………………………………………....……….. 2. Aluminium chloride with water ……………………………………………………………………………....……….. ……………………………………………………………………………....……….. [2]

5 © INNOVA 2008 8872/02 [Turn over For Examiner’s Use (ii) Aluminium chloride sublimes at 179oC and dimerises to form gaseous Al2Cl6 molecules. Draw the structure that represents the vapour at this temperature. [1] (c) Aluminium can form an ion which is isoelectronic with an oxygen ion. (i) Explain what is meant by isoelectronic. ……………………………………………………………………………....……….. ……………………………………………………………………………....………..[1] (ii) State the electronic configuration of the aluminium ion. ……………………………………………………………………………....………..[1] (iii) Sketch and label the shapes of the two types of electron orbital found in the aluminium atoms. [2] (iv) Explain why the first ionisation energy of aluminium atom is less than that of magnesium atom. ……………………………………………………………………………....……….. ……………………………………………………………………………....……….. ……………………………………………………………………………....……….. [2] [Total: 12]

6 © INNOVA 2008 8872/02 [Turn over For Examiner’s Use 3 Ammonia is manufactured by direct synthesis in the Haber process: N2 (g) + 3 H2 (g) 2 NH3 (g) (a) Write an expression for the equilibrium constant, Kc, for this reaction, stating its units. [1] (b) Predict and explain the effect on the position of the equilibrium above when the following changes were made. (i) Increasing the pressure whilst keeping the temperature constant. ……………………………………………………………………………....……….... ……………………………………………………………………………....……….... ……………………………………………………………………………....……….... (ii) Adding finely-divided iron whilst keeping the pressure and temperature constant. ……………………………………………………………………………....……….... …………………………………………………………………