HCI Prelim P2

NAME: _______________________________________ CT: ___________ HWA CHONG INSTITUTION C2 PRELIMINARY EXAMINATION 8872 H1 CHEMISTRY PAPER 2 18 September 2009 2 hours       INSTRUCTIONS TO CANDIDATES 1. This paper consists of 11 printed pages. You should also have a Data Booklet , a set of writing paper and a cover page for Section B. 2. Answer all questions in Section A (Structured Questions) in the spaces provided in this answer booklet. 3. Answer any two questions in Section B (Free Response Questions) on the writing paper provided. Begin each question on a FRESH sheet of writing paper. Tie your answer scripts to Section B behind the cover page provided. 4. At the end of the examination, hand in your answers to Section A and Section B SEPARATELY. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. You may use a calculator. You are reminded of the need for good English and clear presentation in your answers. FOR EXAMINER’S USE TOTAL Multiple Choice Section A (Structured) Section B (Free Response) Q1 / 8 Q5 / 20 Q2 / 16 Q6 / 20 Q3 / 8 Q7 / 20 Q4 / 8 / 30 Subtotal / 40 Subtotal / 40 110 This document consists of 11 printed pages.

HCI(College) 2009 8872/02/C2 Prelim/09 2 Section A Answer all the questions in this section in the spaces provided. 1 (a) Copper exists as 63Cu and 65Cu isotopes. The relative abundance of 65Cu is 30.8. (i) Define the term relative atomic mass. ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... (ii) Calculate the relative atomic mass for copper. (iii) Complete the following table with the number of elementary particles (electrons, protons, and neutrons) that are contained in the ion for the isotope of copper. Ion protons neutrons electrons 63Cu2+ [3] (b) The hydrated double salt, A, Cu(NH4)x(SO4)y.6H2O has a Mr of 399.5. Its formula may be determined from the following experimental data. (i) 2.00 g of salt A was boiled with excess sodium hydroxide. The ammonia expelled was collected by absorption in 40.0 cm 3 of 0.500 mol dm −3 hydrochloric acid in a cooled flask. Subsequently, this solution required 20.0 cm3 of 0.500 mol dm−3 sodium hydroxide for neutralisation. Calculate the mass of ammonium ion present in 2.00 g of salt A.

3 (ii) A second sample of 2.00 g of salt A was dissolved in water and treated with an excess of barium chloride solution. The mass of barium sulfate precipitated, after drying, was found to be 2.33 g. Calculate the mass of sulfate ion in 2.00 g of salt A. (iii) Determine the formula of the hydrated salt A. [5] [Total: 8] HCI(College) 2009 8872/02/C2 Prelim/09

4 2 (a) Element X forms a chloride XCln which melts at 3 C. When 0.500 g of the chloride reacts with an excess of acidified silver nitrate, 1.19 g of AgCl are formed. Another 0.500 g sample of the chloride is heated strongly and chlorine gas is given off. When the residue is treated with an excess of acidified silver nitrate, only 0.714 g of AgC l is precipitated. Calculate a value of n and identify X. [5] (b) The melting points of three chlorides are given below. Compound Formula Melting Point / °C Sodium chloride NaCl 801 Potassium chloride KCl 772 Aluminium chloride AlCl3 180 Explain the difference in the melting points, in terms of structure and bonding, between: (i) NaCl and KCl ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... (ii) NaCl and AlCl 3 ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... [4] HCI(College) 2009 8872/02/C2 Prelim/09

5 (c) Aluminium chloride sublimes at 180 °C. In the vapour phase, an equilibrium is established between aluminium chloride and its dimer. 2AlCl3(g) Al2Cl6(g) Describe and explain the effect on the position of this equilibrium of increasing (i) the pressure ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... (ii) the temperature ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... ……………………………………………………………………………………………….... (iii) Describe and explain, with the aid of a suitable diagram, how the rate of the above reaction is affected by a decrease in temperature. [7] [Total: 16] HCI(College) 2009 8872/02/C2 Prelim/09

6 3 (a) Explain what is meant by the term bond enthalpy. ……...……………………………………………………………………………………………….... ……………...……………………………………………………………………………………….... [1] (b) Gaseous ethanal burns as shown by the following equation: CH3CHO(g) + 2 5 O2(g)  2H2O(g) + 2CO2(g) (i) Using bond energies given in the Data Booklet , calculate the enthalpy change for the combustion of ethanal as shown in the equation above. (ii) Given that the experimentally determined value for enthalpy change of combustion of ethanal is 1160 kJ mol 1, explain the discrepancy between this value and your answer in (b)(i). …………………………………………………… ………………………………………….... …………………………………………………… ………………………………………….... [3] (c) Warfarin is used to destroy rodents and as an anticoagulant (blood thinner) for preventing blood clots after a heart attack. The structural formula of warfarin is as shown. O C C C CH CH2 C OH CH3 O O warfarin HCI(College) 2009 8872/02/C2 Prelim/09

7 Give the structural formula(e) of the organic product(s) formed when warfarin reacts with: (i) hydrogen cyanide with trace potassium cyanide (ii) 2,4-dinitrophenylhydrazine (iii) hydrogen gas in the presence of platinum catalyst [4] [Total: 8] HCI(College) 2009 8872/02/C2 Prelim/09

8 4 For the reaction scheme below, state the reagents and conditions for Reactions I to IV and draw the structures of the organic compounds A to D in the boxes provided. [Total: 8] Reaction I HCI(College) 2009 8872/02/C2 Prelim/09

9 Section B Answer any two questions from this section on separate writing paper. 5 (a) The table below shows the enthalpy changes of hydration ( ∆Hhyd) of some Group II cations and the lattice energies (LE) of their sulfates. Element (M) ∆Hhyd(M2+) /kJ mol−1 LE(MSO4) /kJ mol−1 Ca −1562 −2484 Sr −1413 −2480 Ba −1273 −2374 (i) Describe and explain the trend observed in the enthalpy change of hydration for the given Group II cations. (ii) The enthalpy change of solution ( ∆Hsoln) for barium sulfate is +27 kJ mol −1. Using this data and the information given in the table, determine the enthalpy change of hydration for the sulfate anion. [4] (b) Barium ethanedioate, BaC 2O4, is used as a green pyrotechnic colorant in specialized pyrotechnic compositio ns. It is formed from barium chloride according to the equation below: BaCl2(aq) + Na C O2 2 4(aq)  BaC2O4(s) + 2NaCl(aq) (i) State the types of bonding found in BaC2O4. (ii)