NYJC Prelim CHEM P2

NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAM Higher 1 CANDIDATE NAME CLASS TUTOR’S NAME CHEMISTRY 8872/02 Paper 2 23 Sep 2009 Candidates answer Section A on the Question Paper. 2 hours Candidates answer Section A on the Question Paper Additional Materials: Answer Paper Data Booklet 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. For Examiner’s Use A1 A2 A3 B1 B2 B3 Section A Answer all 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. Total This document consists of 14 printed pages. [Turn over

2 H1 Chemistry 8872/02 NYJC J2/09 Prelim For examiner’s use only Section A Answer all questions in this section in the spaces provided. 1(a) A sample of carbon containing different isotopes was artificially enriched. The relative isotopic masses and its relative abundances determined in a mass spectrometer are given in the table below. Relative isotopic mass Relative abundance 12C 85.0 % 13C 10.0 % 14C 5.0 % Calculate the relative atomic mass of carbon in the sample to 1 decimal place. [1] (b) A 0.100 mol of a hydrocarbon T was burnt completely to produce 26.4 g of carbon dioxide gas and 10.8 g of water. The same mass of W when burnt under a container with 300 g of water at 30 oC was found to bring the water to boil. The process was known to be only 70% efficient. The specific heat capacity of water is 4.2 J g –1 K–1. (i) Determine the molecular formula of the hydrocarbon W. [2]

3 H1 Chemistry 8872/02 NYJC J2/09 Prelim For examiner’s use only (ii) Calculate the enthalpy change of combustion of W. [2] (c) Arranging the following in order of increasing boiling points. Explain your choice in terms of structure and bonding. H 2O, NH 3, NaCl, CH 4 [5] ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... ………………………………………………………………………….........……………... [Total: 10 marks]

4 H1 Chemistry 8872/02 NYJC J2/09 Prelim For examiner’s use only 2 (a) (i) Complete the graph below for the melting points of elements in period 3. [1] (ii) Explain the shape of your graph in terms of bonding and structure. [5] ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... ……………………………………………………………………………………...... 11 12 13 14 15 16 17 18 Melting points

5 H1 Chemistry 8872/02 NYJC J2/09 Prelim For examiner’s use only C C C C C OH H O H OH C O H H H HO H OH H H C C C C C OO H H O H OH C O H H H HO H OH H H C O CO C C OHO H C CH2 OH OH H H HH Step I controlled oxidation Step II cyclic formation Step III C O CO C C OHO H C H H CH2 OH OH (b) The building block for ascorbic acid is the glucose molecule. The following synthetic pathway was proposed: (i) State the type of reaction found in step II and hence circle the functional group(s) present in the intermediate product 1 that is/are involved in the reaction. [3] ……………………………………………………………………………………...... (ii) State the type of reaction present in Step III. [1] ……………………………………………………………………………………...... (c) Aspirin, also known as acetylsalicylic acid is often used as an analgesic (pain- remover) to relieve minor aches and pai ns. It is readily absorbed from the intestines since it diffuses rapidly into the tissues. CO2H OCOCH3 The molecule is hydrolysed by acids in the stomach. (i) Draw the structural formulae of the hydrolysis products. [2] A scorbic Acid Intermediate product 2 Intermediate product 1 Glucose

6 H1 Chemistry 8872/02 NYJC J2/09 Prelim For examiner’s use only Aspirin can be synthesised from 2-methylphenol via the following steps: CO2H OCOCH3 CH3 OH A acidified KMnO4(aq) heat 2-methylphenol Aspirin (ii) Draw the structural formula of the intermediate A. [1] (d) The enthalpy of combustion of Compound A, CH 2=CHCO2H, can be determined either by direct measurem ent of the heat evolved usin g a bomb calorimeter or by indirect method using Hess Law. The energy cycle involving Compound A is given below. CH 2 CHCO2H 3CO2 + 2H2O CH3CH2 CO2H + H2 3O2 + 1/2 O2 H3= -286 kJ mol-1 H2 = -1450 kJ mol-1 H1 = -380 kJ mol-1 +7/2 O2 Hc + H2 3CO2 + 3H2O + (l) (aq) (g) (g)(l) (l) (g) (l) (i) Name the enthalpy change represented by H2 [1] ……………………………………………………………………………………...... (ii) State the type of reaction for H 1. [1] ……………………………………………………………………………………......

7 H1 Chemistry 8872/02 NYJC J2/09 Prelim For examiner’s use only (iii) Using Hess’ Law, calculate the enthalpy change of combustion of compound A. [1] [Total: 16 marks] 3(a) Hydrogen peroxide, H 2O2, is a strong oxidizing agent and is used as an antiseptic. However, it is not stable at room temperature and will undergo decomposition reaction. (i) Draw the dot and cross diagram of H2O2. [1] (ii) State, with reason, the shape about the oxygen atom. [2] ……………………………………………………………………………………...... ……………………………………………………………………………………...... (iii) State the oxidation number of O in the reactants and products. [1] O in H 2O2 : O in H 2O = O in O 2 = (iv) Hence write two balanced half and overall equations for the decomposition of H2O2. [2]

8 H1 Chemistry 8872/02 NYJC J2/09 Prelim For examiner’s use only (b) The rate of H 2O2 decomposition can be catalysed by adding small amounts of MnO2. Using an appropriate diagram, explain in molecular terms, how the presence of MnO2 catalyst increases the rate of decomposition of H2O2. [4]

9 H1 Chemistry 8872/02 NYJC J2/09 Prelim For examiner’s use only (c) An experiment in the laboratory found that iodide ions are oxidized by hydrogen peroxide according to the equation below: H2O2 (aq) + 2H+ (aq) + 2I– (aq)  I2 (aq) + 2H2O (l) Assuming the rate of the above reaction is zero order with respect to [H +], determine the order of reaction with respect to [H 2O2] and [I –] based on the experimental results shown below. H ence determine the value for the rate constant of the reaction, stating the units. Expt [H 2O2] / mol dm⎯3 [I –] / mol dm⎯3 Initial rate / mol dm⎯3 s–1 1 0.01 0.02 0.8 x 10–4 2 0.01 0.03 1.2 x 10