CJC H2 Chem 2012 Prelim P2 QP

CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME CLASS 2T CHEMISTRY 9647/02 Paper 2 Structured Questions Tuesday 21 August 2012 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class in the boxes provided above. Write in dark blue or black pen on both sides of the paper. [PILOT FRIXION ERASABLE PENS ARE NOT ALLOWED] 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 all questions. Write your answers in the space provided. A Data Booklet is provided. 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 of the question. For Examiner’s Use Paper 1 / 40 Q 1 / 12 Paper 2 Q 2 /13 Q 3 /21 Q 4 /12 Q 5 /14 / 72 Q 1 /20 Q 2 /20 Paper 3 Q 3 /20 Q 4 /20 Q 5 /20 / 80 Total / 192 This document consists of 17 printed pages and 0 blank page. [Turn over

2 9647/02/CJC JC2 Preliminary Exam 2012 Eggshells are rich in calcium carbonate and make good plant fertilisers to replenish calcium, an essential nutrient in plant growth. The eggshells are normally crushed and sprinkled around the plants. The shells will slowly decompose and enrich the soil. The decomposition of CaCO 3(s) may be represented as: CaCO3(s) ® CaO(s) + CO2(g) In the laboratory, all Group II carbonates, MCO3, can be decomposed by heating to give the corresponding oxide, MO, and carbon dioxide, CO2. You are to design an experiment to investigate how the rate of decomposition of Group II carbonates varies down the group. In addition to the standard apparatus available in a school laboratory for gas collection, you are provided with the following materials, · samples of carbonates of magnesium, calcium, strontium and barium, · a stopwatch (a) Briefly describe how you would measure the rate of decomposition of the different carbonates in order to enable comparison. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………………………………………………………………………………………………. [1] (b) Draw a diagram of the apparatus and experimental set up that you would use to carry out the experiment. Show clearly the following: · the apparatus used to heat the carbonate, and · how the carbon dioxide will be collected. Label each piece of apparatus used, indicating its size or capacity. [2]

3 9647/02/CJC JC2 Preliminary Exam 2012 [Turn over (c) The temperature of the Bunsen flame varies depending on the ratio of the fuel to oxygen burnt. Besides keeping to the same fuel to oxygen ratio, s uggest how you would control another factor in the heating to ensure a fair comparison of the rate of decomposition of different carbonates. ……………………………………………………………………………………………………. …………………………………………………………………………………………………. [1] (d) Other than the use of safety goggles, state one hazard that must be considered when planning the experiment and suggest how you would keep this risk to a minimum. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………………………………………………………………………………………………. [2] (e) With reference to the apparatus in (b), show how you would calculate the mass of each carbonate used in the experiment. [M r: MgCO3 = 84.3; CaCO3 = 100.1; SrCO3 = 147.6; BaCO3 = 197.0] [2]

4 9647/02/CJC JC2 Preliminary Exam 2012 (f) Draw a table with appropriate headings (and units) to show the data you would record and the values you would calculate in order to plot a suitable graph to show the variation in the rates of decomposition of the carbonates. Sketch, and explain, the shape of the graph you would expect from your results. Label clearly the axes. Explanation: ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………………………………………………………………………………………………. [4] [Total: 12]

5 9647/02/CJC JC2 Preliminary Exam 2012 [Turn over 2 (a) Carbon dioxide is used in beverage carbonation. Cylinders of pressurised carbon dioxide are used to produce carbonated drinks. One such cylinder has an internal volume of 3.0 dm3 and contains 4.6 kg of carbon dioxide. (i) Calculate the pressure (in Pascals) the carbon dioxide gas would exert inside the cylinder at 28 °C. (ii) To find the pressure of a fixed amount of c arbon dioxide gas under certain conditions, the van der Waals’ equation given below should be used. T R n b) n (VV n ap 2 2 = -÷ø öçè æ + Without further calculation, explain how the pressure obtained using the van der Waals’ equation would differ from that in (a)(i). ………………….…………………………………………………………………………….. ………………….…………………………………………………………………………….. [3] (b) Real gases like carbon dioxide can be liquefied at low temperatures just by applying pressure. Gases can be liquefied by pressure alone if the temperature is below their critical temperature, T c. At temperatures above T c, the gas cannot be liquefied, regardless of the pressure applied. The critical temperature of carbon dioxide is 31.1 °C. (i) Explain why real gases like carbon dioxide can be liquefied just by applying pressure. ………………….……………………………………………………………………………. ………………….……………………………………………………………………………. (ii) By considering structure and bonding, suggest a value for the critical temperature of methane and give a reason for your choice. ………………….……………………………………………………………………………. ………………….……………………………………………………………………………. ………………….……………………………………………………………………………. [2]

6 9647/02/CJC JC2 Preliminary Exam 2012 (c) Beyond the critical temperature and pressure, carbon dioxide exists as a supercritical fluid, a state that resembles a gas but has density closer to that in the liquid phase. Carbon dioxide is now well established as a solvent for use in extraction. (i) Suggest a reason why supercritical carbon dioxide is preferred as a solvent to extract caffeine from solid coffee over organic solvents like benzene. ………………….……………………………………………………………………………. ………………….……………………………………………………………………………. ..………………….…………………………………………………………………………... (ii) Suggest why small amounts of ethanol need to be added to supercritical carbon dioxide to increase the solubility of polyphenols for extraction. An example of a polyphenol is shown below. H3CO HO OH ……………..………………………………………………………………………………..… ………………….……………………………………………………………………………… ……………..………………………………………………………………………………….. [2] (d) Ethanedioate ions, C 2O42–, can be oxidised by hot acidified aqueous potassium manganate(VII) to form carbon dioxide. (i) Draw the structure of ethanedioate ions, C 2O42-, and give the bond angle around the central carbon atom.

7 9647/02/CJC JC2 Preliminary Exam 2012 [Turn over (ii) Construct a balanced equation for the reaction between ethanedioate ions and hot acidified potassium manganate(VII). (iii) 1.63 g of a salt, KHC 2O4∙H2C2O4, was dissolved in distilled water and made up to 250 cm3 solution. Calculate the volume of 0.020 mol dm –3 KMnO4 required to react with 20.0 cm3 of the KHC2O4∙H2C2O4 solution. [Mr of KHC2O4∙H2C2O4 = 218.1] [4] (e) (i) The reaction between acidified potassium manganate( VII) and ethanedioate ions is usually carried out at a higher temperature of 60 °C . Suggest why the rate of this reaction is slow at room temp