2013 TPJC H1 Chemistry P2 QP

TPJC_2013_8872_02 [Turn over TAMPINES JUNIOR COLLEGE JC2 Preliminary Examination CANDIDATE NAME TUTOR NAME 1 2 CHEMISTRY Paper 2 Candidates answer Section A on the Question Paper. Additional Materials: Answer Paper Data Booklet 8872/02 Thursday, 05 September 2013 2 hours H1 CIVICS GROUP For Examiner’s Use Section A B5 B6 B7 Total READ THESE INSTRUCTIONS FIRST Write your name and civics group on all the work you hand in. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all the questions. Section B Answer two questions on separate answer paper. 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. This document consists of 14 printed pages.

2 TPJC_2013_8872_02 Section A Answer all questions in this section in the spaces provided. For Examiner’s Use 1 Radiotherapy is the medical use of radiation generated from radioactive isotopes to destroy or weaken malfunctioning cells. Examples of radioactive isotopes used for the therapy are those of iodine, phosphorus and lutetium. (a) Lutetium has two naturally occurring isotopes, 175Lu and 176Lu. Their natural abundances are 97.4% and 2.6% respectively. (i) Define the term relative atomic mass. …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….…… (ii) Calculate, to one decimal place, the relative atomic mass of lutetium. [2] (b) 176Lu has a half-life of 101078.3 × years. The half-life of a radioactive isotope is the time taken for half of the atoms in a given mass to decay. Calculate the percentage of a sample of 176Lu isotopes remaining after 1110134.1 × years. [2] Iodine-131 is used to treat the thyroid for cancers and phosphorus-32 is used to control the excess of red blood cells produced in the bone marrow. (c) Complete the table below for the 131I and 32P isotopes. Isotope Number of protons Number of neutrons 131I 32P [1]

3 TPJC_2013_8872_02 [Turn over Radioactive isotopes are commonly incorporated into compounds to trace the path of biochemical reactions. These compounds are known as radioactive tracers. The structure of fluorodeoxyglucose (18F-FDG), a radioactive tracer widely used in medical imaging, is shown below. O OH OH F18 OH OH For Examiner’s Use 18F-FDG (d) (i) Apart from ether (–O–), circle and name the functional groups that are present in the 18F-FDG shown above. (ii) Calculate the percentage composition by mass of carbon in 18F-FDG. (iii) Would you expect 18F-FDG to be soluble in water? Explain your answer. …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….……

4 TPJC_2013_8872_02 (iv) 18F-FDG is heated under reflux with an excess of the following isotopically labelled carboxylic acid in the presence of concentrated sulfuric acid. CCH3 O18 O H For Examiner’s Use Give the structural formula of the organic product formed and state the type of reaction that has occurred. You may assume that the ether group is inert. [7] [Total: 12] 2 In an alkaline fuel cell, the chemical energy from the hydrogen fuel supplied to one electrode is converted into electricity through a chemical reaction with the oxygen supplied to the other electrode. These two electrodes are connected using potassium hydroxide as an electrolyte. A simplified diagram of the fuel cell is shown below. The two half-equations for this cell are 2H2O + 2e− H2 + 2OH− O2 + 2H2O + 4e− 4OH− Load KOH O2 product H2 electrodes

5 TPJC_2013_8872_02 [Turn over (a) (i) Combine these two half-equations to show the overall reaction occurring in the cell. For Examiner’s Use (ii) Use oxidation numbers to show which species in your equation is reduced and which is oxidised. [4] Porous graphite impregnated with suitable catalysts could be used as electrodes for an alkaline fuel cell. (b) (i) Describe the structure of, and the bonding in, the element graphite. Draw a diagram to illustrate your answer. …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….……

6 TPJC_2013_8872_02 (ii) State a physical property of graphite that metals also possess. Explain, in terms of the bonding present, why it possesses this property. For Examiner’s Use property ………………………………………………………………………….. explanation ………………………………………………………………….…… …………………………………………………………………………...….……..[4] [Total: 8] 3 This question is about period three elements and their compounds. (a) (i) Sketch on the axes provided, the trend in first ionisation energy across period three. (ii) Explain the general trend in first ionisation energy of period three elements. …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….…… (iii) Explain the difference between the values of the first ionisation energies of phosphorus and sulfur. …………...…………..………………………………………………………….…… …………...…………..………………………………………………………….…… …………...…………..………………………….……………………..………….[3] first ionisation energy / kJ mol−1 Na Mg Al Si P S Cl Ar

7 TPJC_2013_8872_02 [Turn over (b) Sulfuryl chloride, SO2Cl2, decomposes as follows when heated to 100 °C. For Examiner’s Use SO2Cl2(g) SO2(g) + Cl2(g) (i) Calculate the equilibrium constant, Kc, at 100 °C, given the following values: [SO2Cl2] = 14.6 g dm−3, [SO2] = 3.33 g dm−3, [Cl2] = 11.5 g dm−3. (ii) Draw a dot-and-cross diagram for sulfuryl chloride. (iii) Complete the electronic configuration of a chlorine atom. 1s2 ……………………………………………….. Hence describe the bonding in the Cl2 molecule in terms of orbital overlap. Include a diagram in your answer. [7] [Total: 10]

8 TPJC_2013_8872_02 4 An airbag is a vehicle safety device which is designed to inflate rapidly during an automobile collision. Its purpose is to cushion occupants during a crash and provide protection to their bodies when they strike interior objects such as the steering wheel or a window. An airbag typically contains a mixture of sodium azide (NaN3), potassium nitrate (KNO3) and silicon dioxide (SiO2). Within about 40 milliseconds of impact, all these components react in three separate reactions as described in order below. The first reaction is the decomposition of sodium azide to produce sodium metal and nitrogen gas. The equation is as follows. 2NaN3 → 2Na + 3N2 The highly reactive sodium metal formed then reacts with potassium nitrate to produce more nitrogen gas according to the following equation. 10Na + 2KNO3 → K2O + 5Na2O + N2 The third reaction involves the removal of K2O and Na2O by silicon dioxide to produce the metal silicates, K2SiO3 and Na2SiO3. The airbag is inflated by the nitrogen gas produced in the first and second reactions. For Examiner’s Use (a) (i) Calculate the amount, in moles, of sodium metal and of nitrogen gas formed when 110 g of sodium azide in an airbag is decomposed.