RVHS H2 Chem 2012 Prelim P3 QP

CANDIDATE NAME CLASS CENTRE NUMBER RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION 6 S INDEX NUMBER H2 CHEMISTRY 9647/03 Paper 3 Free Response 18 September 2012 2 hours Candidates answer on separate paper. Additional Materials:Answer Paper Cover Page Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class, centre number and index number on all the work you hand in. Write in dark blue or black pen on both sides of 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 any four questions. Begin each question on a fresh sheet of paper. A Data Booklet is provided. Do not write anything on it. You are reminded of the need for good English and clear presentation in your answers. 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, with the cover page on top. _______________________________________________________________________________ This document consists of 11 printed pages and 1 blank page. River Valley High School 9647/03/PRELIM/12 [Turn over Preliminary Examination 2012

2 River Valley High School 9647/03/PRELIM/12 [Turn over Preliminary Examination 2012 Answer any four questions. 1 (a) One common characteristic of transition elements is the ability to form complexes. Transition elements react with carbon monoxide to form a class of complexes known as metal carbonyls. One aspect of metal carbonyls that is unusual for metallic compounds is that they are often volatile. N ickel carbonyl was first synthesised in 1890 by Ludwig Mond by passing carbon monoxide over nickel metal. Nickel carbonyl has a boiling point of 43 °C and is extremely poisonous. (i) Draw the ‘dot-and-cross’ diagram of carbon monoxide. (ii) Explain in terms of structure and bonding why nickel carbonyl has a low boiling point. (iii) A 2.00 g sample of nickel carbonyl was vaporised and found to occupy a volume of 314 cm 3 at 50 °C and 1 atmosphere pressure. Determine the Mr of nickel carbonyl. (iv) Nickel carbonyl has the general formula Ni(CO) x. Using the answer in (iii) , determine the coordination number of nickel in nickel carbonyl and suggest the shape of the complex. [7] (b) Transition metal compounds are often coloured. (i) Explain why transition metal compounds are often coloured. (ii) When a solution of dilute sulfuric acid was electrolysed using copper electrodes, a blue solution was obtained. On heating this solution to dryness, an anhydrous white solid was eventually obtained. When concentrated hydrochloric acid was electrolysed using copper electrodes in a separate experiment , a yellow solution was obtained. On adding water, the colour of the solution turned from yellow to green and eventually blue. Explain these observations. State clearly the formula of any coloured species. [9]

3 River Valley High School 9647/03/PRELIM/12 [Turn over Preliminary Examination 2012 (c) Menthol, menthone and limonene are members of a class of compounds called isoprenoids which are derived from isoprene, CH2=C(CH3)CH=CH2. Limonene and menthone are intermediates in the bios ynthesis of menthol. The many reactions in the biosynthesis of menthol are catalysed by different enzymes. In the laboratory, transition metal catalysts can be used to catalyse many of these reactions instead of enzymes. OO OOHH limonene menthone menthol Describe how you would distinguish these three compounds by means of simple chemical tests. [4] [Total: 20]

4 River Valley High School 9647/03/PRELIM/12 [Turn over Preliminary Examination 2012 2 (a) Hydrocarbons like alkanes are commonly used for fuels. Increasingly, biofuels are gaining increased public and scientific attention, driven by concerns over oil prices and greenhouse gas emission. Biofuels, like methanol and butan-1- ol, which can be produced by the fermentation of biomass, are increasingly being used for fuels over hydrocarbons. (i) Using common oxidation numbers for H and O, calculate the oxidation number of carbon in methanol, CH3OH. (ii) Using only the elements C, H and O, suggest the structural formulae of two compounds, each containing a single carbon atom with an oxidation number of zero and +2 respectively. In an experiment to determine the standard enthalpy change of combustion of butan-1- ol, DHc,, a quantity of the fuel was burned underneath a 200 g copper can containing 515 g of water. It was found that the temperature of water rose from 23 °C to 58 °C after 2.30 g of butan-1-ol has been burned completely. (iii) Write an equation for the complete combustion of butan-1-ol. (iv) Using the experimental results and relevant data from the Data Booklet, calculate the apparent D Hc, of butan -1-ol. You can ignore the heat capacity of the copper can. (v) The true value of D Hc, of butan-1-ol is -2670 kJ mol-1. Compare this value to the one you have calculated in (iv) and suggest a reason for the discrepancy. [7] (b) The following table compares the pKa values of two dicarboxylic acids. HO2C-(CH2)n-CO2H HO2C-(CH2)n-CO2 - -O2C-(CH2)n-CO2 - pK1 pK2 acid formula p K1 p K2 propanedioic acid HO2CCH2CO2H 2.85 5.70 butanedioic acid HO2CCH2CH2CO2H 4.20 5.60 (i) Suggest a reason why the pK 1 value of propanedioic acid is so much less than the pK1 of butanedioic acid. (ii) Suggest a reason why the pK 2 value of propanedioic acid is higher than its pK1 value. (iii) Calculate the pH of 0.25 mol dm -3 of butanedioic acid (ignoring the effect of pK2 on the pH).

5 River Valley High School 9647/03/PRELIM/12 [Turn over Preliminary Examination 2012 (iv) Sketch the pH -volume added curve you would expect to obtain when 60 cm3 of 0.25 mol dm-3 NaOH is added to 20 cm 3 of 0.25 mol dm-3 butanedioic acid. On your curve, include all relevant information and highlight any buffer regions. [7] (c) When chlorine gas is passed over heated aluminium in a hard glass tube, a vapour is produced which condenses to a yellow -white solid. At low temperatures, the vapour has the empirical formula A lCl3 and an Mr of 267. (i) Suggest the molecular formula of the vapour, and draw a ‘dot-and-cross’ diagram to describe the bonding. The yellow-white solid reacts with water in two different ways. When a few dro ps of water are added to the solid, steamy white fumes are evolved and a white solid remains, which is insoluble in water. When a large volume of water is added to the solid, a clear, weakly acidic solution is produced. (ii) Write equations, including state symbols, for these two reactions and explain the observations. [6] [Total: 20]

6 River Valley High School 9647/03/PRELIM/12 [Turn over Preliminary Examination 2012 3 Alcohols and ketones are two classes of organic compounds with great importance in both industrial processes and in biological systems. (a) The iodination of propanone under acidic conditions is shown by the following equation: CH3COCH3(aq) + I2(aq) ® CH3COCH2I(aq) + H+(aq) + I –(aq) The rate of the reaction was studied via a colorimetric method, in which the colour intensity of iodine was measured at regular intervals. Three sets of separate experiments were performed in which the initial concentration of iodine, propanone and acid was varied in turn, with the other two being kept constant. The results are shown in Graphs 1 and 2 below: [CH3COCH3] = 0.10 mol dm–3 [CH3COCH3] = 0.17 mol dm–3 [CH3COCH3] = 0.25 mol dm–3 [I2]/ mol dm–3 time/ min Graph 1 [H+] = 0.20 mol dm–3 [H+] = 0.40 mol dm–3 [H+] = 0.60 mol dm–3 [I2]/ mol dm–3 time/ min Graph 2

7 River Valley High School 9647/03/PRELIM/12 [Turn over Preliminary Examination 2012 (i) Suggest another method, other than a colorimetric method, that