NYJC Prelim CHEM P3

NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9746/03 Paper 3 16 September 2009 2 hours Candidates answer on writing paper Additional Materials: Data Booklet Graph paper READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. 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 4 out of 5 questions. Write your answers on the writing paper provided Begin each question on a fresh piece of paper. You are advised to show all working and calculations This document consists of 9 printed pages and 1 blank page H2 Chemistry 9746/03/NYJC J2/09PX

2 H2 Chemistry 9746/03/NYJC J2/09PX Turn over 1 Aluminum is an element in Period 3 of the Periodic Table. (a) The graph below shows the second ioniza tion energies of eight elements with consecutive proton number. (i) Which of the above elements, A to H, is Aluminium? Explain your answer. [2] (b) A 0.400g sample of a mineral, AB(CO 3)2 (where A and B are Group II elements) was heated strongly until no further change occurs. A white powder weighing 0.275g was collected and shaken with 200 cm 3 of water. A portion of the white powder remained insoluble and was then filtered. The residue was dri ed and it weighed 0.057g. (i) Assuming that the products on heat ing consist of the oxides of A and B and carbon dioxide, write a balanced equation for the decomposition of AB(CO3)2 [1] (ii) Calculate the mass of carbon dioxide produced. [1] (iii) Hence, or otherwise, identify the metals, A and B , showing your working clearly. [2] (c) Arrange the following molecules in order of increasing boiling points. Explain your choice in term of structure and bonding. NaF, H 2O, MgO, CO 2, CH 3NH2 [5]

3 H2 Chemistry 9746/03/NYJC J2/09PX Turn over d(i) Which of the following amino acid residues is most likely to be found on the outer surface of a water soluble globular protein? Explain your answer. H2NC H C CH2 OH O phe H2NC H C (CH2)4NH2 OH O Lys H2NC H C CH2 OH O OH Ser HN C OH O Pro H2NC H C CH2 OH O CH CH3 CH3 Leu [2] (ii) State the type of R group interactions that would occur between these residues. [1] (iii) The white of an egg is about 88% wate r and 12% protein (by mass). When an egg is heated, the white undergoes obvious changes. Name the process responsible for thes e changes and explain the structural changes which the food components undergo. [3] (iv) Amino acids exist as zwitterions in aqueous solutions. Choose any one of the five amino acids, draw the structural formula of its zwitterions formed. [1] (v) Write equations to show how it can act as a buffer. [2]

4 H2 Chemistry 9746/03/NYJC J2/09PX Turn over 2(a) (i) Using the data given below and other relevant data from the Data Booklet, draw a clearly labelled ener gy level diagram for Fe 2O3(s) and hence calculate its lattice enegy Data: Enthalpy change of atomization of iron = +414 kJ mol-1 First electron affinity of oxygen = -141 kJ mol-1 Second electron affinity of oxygen = +844 kJ mol-1 8Fe(s) + 6O2(g)  4Fe2O3 (s) H = -3288 kJ mol-1 [4] (ii) Explain why the second electron affinity of oxygen is endothermic. [1] (iii) Using the data provided below, draw a energy cycle di agram to calculate the enthalpy change, Hr of the reaction: 3C(s) + 2Fe2O3 (s)  4Fe(s) + 3CO2(g) Data: Enthalpy change of combustion of graphite = -394 kJ mol-1 8Fe(s) + 6O2(g)  4Fe2O3(s) Hr = -3288 kJ mol-1 [4] (b) Describe a simple chemical test which would enable you to distinguish the following pairs of compounds. For each test, state the reagents and conditions, and state what would be observed with each compound. Note: The distinguishing of the pair may re ly on preliminary breaking up of the compounds and subsequent testing of the reaction products. (i) CH2CHO CONH2 A & B (ii) O O C H3 C H3 O O CH3 CH3 X & Y [4]

5 H2 Chemistry 9746/03/NYJC J2/09PX Turn over (c) Nicotine is a naturally occurring liquid alkaloid, which can be extracted from the leaves of the tobacco plant. It is the compound that is responsible for the potent effect of tobacco on the human body. nicotine N N CH3 .. : (i) A molecule of nicotine contains two ni trogen atoms, both of which can act as a base by accepting a proton. Draw the structure of nicotine and circle the nitrogen atom which you think is the stro nger base. Explain your choice for that nitrogen acting as the stronger base. [3] (ii) As a result of the solubility in wate r, it is readily absorbed both through the watery mucous membrane of the mouth and through the fatt y cells that line the lungs. Draw a diagram, including dipoles, to show the hydrogen bonding between a molecule of nicotine and a molecule of water. [2] (d) Another organic compound P has two different nitrogen atoms in its structure. H2N CH2 CH2 CH2 C NH2 O (i) Draw an isomer of compound P which exhibits optical activity. [1] (ii) Draw the structure of t he organic compound formed when P reacts with hot HCl (aq) [1] Compound P

6 H2 Chemistry 9746/03/NYJC J2/09PX Turn over 3(a) Dinitrogen oxide, N 2O, is used as an anesthetic. It decomposes when heated as follows. N 2O (g)  N2 (g) + ½ O2 (g) The rate of decomposition of pure dinitr ogen oxide may be followed by measuring the total pressure of the system. In an experiment conducted at 1000K, in the presence of a gold surface, the total pressure PT increased as follows : PT / kPa 25.0 27.5 30.0 32.5 34.0 35.0 Time / s 0 100 230 420 590 740 PN2O / kPa 25.0 20.0 * 10.0 * 5.0 (i) Calculate the partial pressures of N2O ( PN2O ) at 230 s and 590 s. [3] (ii) a graphical method, determine the order of the reaction with respect to N2O. [4] (iii) ld have elapsed for the partial pressure of N2 to increase to about 18.8 kPa. [3] (b) xture of Mg(NO 3)2 and Y(NO 3)2 is dissolved in water, a blue solution is cipitation olves. pon filtration, a dark blue filtrate and white residue are obtained. (i) the electronic configuration (s,p,d,f notation) for cation Y , and identity of X [2] (ii) ns, describe the reactions and state the colour of any precipitate formed. [4] (c) with hydrogen cyanide to form a compound with molecular formula C4H7ON. (i) Draw a displayed formula for the compound obtained. [1] (ii) (i) can be used in the synthesis of methyl-2- methylpropanoate. By using Estimate how many half liv es wou When a mi observed. An unknown X (aq) is t hen added dropwise to the blue solution. Pre occurs. When excess X (aq) is added, some of the precipitate diss U For Y and X (aq), write By means of equatio Propanone reacts The compound in C CH3 H2C C O OH3C Outline a reaction scheme, stati ng reagents and conditions for the conversion. [3]

7 H2 Chemistry 9746/03/NYJC J2/09PX Turn over -34(a) 40.0 mol dm of 0.120 cm3 hydrochloric acid so