JJC H1 CHEM P2 ANS

JURONG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME CLASS CHEMISTRY 8872/02 Paper 2 Structured 28 August 2009 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. A Data Booklet is provided. Do not write anything on the Data Booklet. 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. For Examiner’s Use Section A B5 B6 B7 Total This document consists of 11 printed pages and 1 blank page. [Turn over Page 1 of 16

Section A Answer all questions in this section in the spaces provided. 1. (a) Complete the table below. Number of Particle Electric charge Mass number Protons Electrons Neutrons X 0 32 16 16 16 Y 1- 81 35 36 46 Z 3- 70 31 28 39 [2] (b) Beams consisting of particles X, Y and Z are subjected to an electric field as shown in the diagram below. Sketch, and label, on the diagram below to show how beams of each of the three particles are affected by the electric field. [3] (c) Using the grid provided below, sketch a graph of the seven successive ionisation energies for element X. [2] [Total:7] + – X, Y, Z Y X Z Ionisation Energy / kJ mol-1 0 1 2 3 4 5 6 7 2m No. of electrons Page 2 of 16

2. (a) On heating, sodium nitrate, (NaNO 3) decomposes giving the sodium nitrite, (NaNO2) and oxygen while magnesium nitrate, (Mg(NO 3)2), decomposes giving magnesium oxide, nitrogen dioxide and oxygen. (i) Write balanced equations for the decomposition of sodium nitrate and magnesium nitrate respectively. NaNO3 → NaNO2 + ½ O2 1m Mg(NO3)2 → MgO + 2NO2 + ½ O2 1m [2] (b) (i) 5.35 g of a mixture of sodium nitrate, (NaNO3) and magnesium nitrate, (Mg(NO3)2), was heated in a fume cupboard until no more gases were evolved. The sodium nitrite, (NaNO 2), formed was dissolved in water to form a 250 cm 3 solution of nitrite ions, NO 2 . The nitrite ions in the solution reacted with 40.00 cm 3 of acidified potassium manganate(VII) solution. The nirite ion half equation is given by: NO2  + H2O NO3  + 2H+ + 2e Write a balanced equation for the reaction between nitrite ions and manganate(VII) ions. 5NO 2  + 2MnO4 - + 6H+ 5NO3  + 2Mn2+ + 3H2O 2m [2] (ii) Given that the concentration of the acidified potassium manganate(VII) solution was 0.200 mol dm 3, calculate the number of moles of potassium manganate(VII) that reacted. No. of moles of MnO4 - = 0.200 x 40/1000 = 8.00 x 10-3 1m [1] (iii) Calculate the number of moles of sodium nitrite, (NaNO 2), in 250 cm 3 of the solution. No. of moles of NaNO2 = 8.00 x 10-3 x 5/2 = 2.00 x 10-2 1m [1] Page 3 of 16

2. (b) (iv) Calculate the number of moles of sodium nitrate, (NaNO3), in 5.35 g of the mixture. No. of moles of NaNO 3 = 2.00 x 10-2 1m [1] (iv) Hence calculate the respective mass of sodium nitrate, (NaNO 3) and magnesium nitrate, (Mg(NO3)2), in the mixture. Mass of NaNO3 = 2.00 x 10-2 X Mr = 1.70 g 1m Mass of Mg(NO3)2 = 5.35 – 1.70 = 3.65 g 1m [2] [Total: 9] 3. Propane, C3H8, is isolated from bottled gas used for cooking and heating. (a) Write an equation for the complete combustion of propane. C3H8 + 5O2 → 3CO2 + 4 H2O 1m [1] (b) The density of propane is 1.83 g dm -3. (i) Calculate the number of moles of propane present in 50 cm3. No. of moles of propane = (50/1000 X 1.83 ) / 44 = 2.08 x 10-3 1m Page 4 of 16

3. (b) (ii) Calculate the volume of oxygen (measured at room temperature and pressure) that would be required to completely burn 50 cm 3 of propane. Volume of propane = 5 x 50 = 250 cm3 / 0.250 dm3 2m [4] (c) (i) Write an equation which represents the standard enthalpy change of formation of gaseous propane. 3C(graphite) + 4H2(g) → C3H8 (g) 1m (ii) Use the following standard enthalpy changes of combustion, ΔH c , to calculate the standard enthalpy change of formation of propane. substance ΔHc  / kJ mol-1 carbon –393 hydrogen –286 propane –2219 ΔHf = 3(–393) + 4(–286) –(–2219) = – 104 kJ mol-1 1m substitution 1m ans + units [3] (d) Given that the activation energy for the standard enthalpy change of formation of propane is 100 kJ mol 1, draw a labelled energy profile diagram for the reaction. [2] [Total: 10] 4H2 + 3C C3H8 100 kJ mol -1 – 104 kJ mol - 1 2m Reaction Potential Energy / kJ mol -1 Page 5 of 16

4. (a) For the following two conversions, state clearly the reagents and conditions required in each step. Draw the structure of intermediate P formed in the box provided. (i) (ii) (iii) Intermediate P Reagents and conditions: Step1: _____hot acidif ied KMnO4__1m Step 2: __CH3CH2OH, concentrated H2SO4, heat 1m CH3CH2COOH 1m Step 2 CH3CH2C OCH2CH3 NaOH(aq) heat under reflux O CH3CH2CH2OH Step 1 Step 3 A & B Draw the structures of products A and B. State the type of reaction for Step 3. A B Type of reaction:_hydrolysis ___ 1m Intermediate P can be synthesized from ethanol in 3 steps as shown beolw: CH3CH2OH X Y Intermediate P Draw structures of X and Y in the boxes below. X Y [8] CH3CH2COO-Na+ 1m CH3CH2OH 1m CH3CH2Cl or CH3CH2Br 1m CH3CH2CN 1m Page 6 of 16

4. (b) Draw the structures of the organic products formed when butan-2-ol reacts with the following reagents: (i) Hot acidified potassium dichromate(VI). CH3COCH2CH3 1m (ii) Alkaline aqueous iodine CH 3CH2COO- + CHI3 1m (iii) Na CH 3CHCH2CH3 1m [3] (c) Butan-2-ol reacts with hot concentrated sulphuric acid to form two isomers M and N. M exhibits stereoisomerism while N does not. (i) Draw the structure of N. CH=CHCH 2CH3 1m (ii) With the aid of diagrams, show how M exhibits stereoisomerism. C=C C=C [3] [Total: 14] O-Na+ H CH3 CH3 H H H CH3 CH 3 1m 1m Page 7 of 16

Section B Answer two of the three questions in this section on separate paper. 5. This question is about ethanoic acid and methanol. (a) Vinegar is a dilute solution of ethanoic acid, CH3COOH. (i) Write an expression for the acid dissociation constant, Ka, for ethanoic acid. Ka = [CH3COO][H+]/[CH3CO