YJC H2 CHEM P2

This question paper consists of 11 printed pages. YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE Parent’s Signature: CANDIDATE’S NAME: ______________________________ CTG: _________ YISHUN JUNIOR COLLEGE PRELIMINARY EXAMINATION 2009 CHEMISTRY 9746/02 HIGHER 2 Wednesday 26 AUGUST 2009 0800hrs − 0930hrs (1 hour 30 minutes) Additional materials: Data Booklet For Examiner’s Use Paper 2 1 / 11 2 / 12 3 / 15 4 / 9 5 / 13 READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, name and CTG on all the work that 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 paper clips, highlighters, glue or correction fluid. Answer all questions. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. Overall / 60

2 Answer all questions in the spaces provided 1 The elements in the Periodic Table form the building blocks of all substances and can be broadly classified as metals and non-metals. (a) Potassium and copper are metals from Period 4 of the Periodic Table. Potassium is a soft, silvery white metal that tarnishes readily in air. Copper is a hard, reddish metal that is resistant to corrosion at ordinary temperature. Metallic potassium has no commercial uses, but copper is used widely to make electrical wires. Data about potassium and copper are given as follows: atomic radius / nm density / g cm3 potassium 0.221 0.826 copper 0.117 8.95 (i) Given the electronic configuration of potassium below, write down the full electronic configuration of copper below. potassium: 1s2 2s2 2p6 3s2 3p6 4s1 copper: (ii) Although copper has more electrons than potassium, the atomic radius of copper is smaller than that of potassium. Account for the difference in atomic radii of the two elements. (iii) By considering the arrangement of particles in a metallic lattice, suggest an explanation for the difference in the densities of the two metals. [5] 9746 / YJC / 2009 / Preliminary Examination / Paper 2

3 (b) The hydrides of group VII elements are dissociated at high temperatures according to the equation: 2HX(g)  H2(g) + X2(g) (i) With reference to relevant data from the Data Booklet, describe and explain the trend observed in the relative stabilities of the hydrides of chlorine, bromine, and iodine. (ii) State the intermolecular force responsible for the higher boiling point for the hydride of fluorine, compared to the hydrides of chlorine, bromine, and iodine, despite having a much lower relative molecular mass. [4] (c) Helium and neon are non-metals from Group 0 of the Periodic Table. These elements exist as monoatomic gases and are commonly used in advertising tubes. When a minimum potential difference of 24.0 V is supplied to an advertising tube containing helium, the gaseous atoms gain sufficient energy to become ionised. Use relevant data from the Data Booklet to estimate the minimum potential difference required to ionise neon in an identical advertising tube. [2] [Total: 11] 9746 / YJC / 2009 / Preliminary Examination / Paper 2

4 2 Calcium oxalate, CaC 2O4, is a white needle-like crystalline solid. On strong heating, calcium oxalate decomposes to produce carbon monoxide. (a) (i) Draw a ‘dot-and-cross’ diagram to illustrate the bonding of the anion in CaC2O4. (ii) Hence, draw the shape of the anion in CaC 2O4, showing the values of the bond angles. [3] (b) When 0.128 g of anhydrous CaC 2O4 was heated at 400 C until no further change in mass is observed, a white solid B and 0.028 g of carbon monoxide gas is obtained. No other substances were formed. (i) Suggest and explain one precaution that should be taken when heating calcium oxalate in the laboratory. (ii) Given that 1 mole of CaC 2O4 decomposes to form 1 mole of B, use the information given to determine the Mr of B. 9746 / YJC / 2009 / Preliminary Examination / Paper 2

5 (iii) Based on your answer in (ii), suggest the identity B. (iv) Hence, write a balanced equation for the thermal decomposition of calcium oxalate. (v) Predict a value for the thermal decomposition temperature for barium oxalate, given that it is 400 C for calcium oxalate. Explain your reasoning. [9] [Total: 12] 3 Propanone is a useful organic solvent due to its ability to dissolve a variety of compounds. (a) Propanone can be synthesised in the laboratory from 1 −chloropropane by a method which involves one intermediate product A. (i) Write the formula of A and B in the space above. A HC C C Cl H H H H H H KOH, CH3CH2OH reflux Step II B HC C C H H H OH H Step III 9746 / YJC / 2009 / Preliminary Examination / Paper 2

6 (ii) Suggest reagents and conditions for Step II: Step III: [4] (b) Propanone undergoes nucleophilic addition with hydrogen cyanide in the presence of a trace of sodium hydroxide to form a cyanohydrin. (i) Write an equation to show how the nucleophile is generated. (ii) Outline the mechanism of the reaction, using curly arrows to show the movement of electrons during the reaction. (iii) The cyanohydrin formed can be convert ed into 2-hydroxy-2methylpropanoic acid. Suggest reagent and conditions for this reaction. [4] (c) 2-hydroxy-2-methylpropanoic acid (can be represented as HA), is a monoprotic weak acid with an acid dissociation constant, K a, of 2.05 x 10−5 mol dm−3. In an experiment, 20.0 cm 3 of 0.100 mol dm −3 2-hydroxy-2-methylpropanoic acid was titrated with 0.200 mol dm−3 aqueous sodium hydroxide. (i) Calculate the pH of the acid solution before any sodium hydroxide has been added. 9746 / YJC / 2009 / Preliminary Examination / Paper 2

7 (ii) Calculate the volume of