RVHS H2 CHEM P2 Prelim

RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9647/02 Paper 2 Structured Questions 13 September 2011 2 hours Candidates answer on the Question Paper. Additional Materials: 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 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. Answer all questions. A Data Booklet is provided. Do not write anything on it. 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. For Examiner’s Use 1 2 3 4 5 Total ____________________________________________________________________________ This document consists of 18 printed pages.

River Valley High School 9647/02/PRELIM/11 [Turn over Preliminary Examination 2011 2 Answer all questions in the space provided. 1. Planning (P) John went on an excursion to a limestone cave in Gunung Mulu National Park, Sarawak. In there, he picked up a limestone rock and decided to investigate the percentage by mass of CaCO3 in this rock sample. When he was back in his school laboratory, he weighed the rock sample and the reading was 0.200 g. (a) 2H+ + CO3 2 CO2 + H2O Given the equation above, draw a labelled experimental setup of how collection of CO2 gas can be achieved. [3] (b) Given that the percentage by mass of CaCO 3 in the limestone rock sample is at least 60% and assuming that other substances in the rock sample are inert to acid, calculate the volume of 0.100 mol dm3 of HCl that should be used to react with the rock sample. Ar: Ca, 40.1; C, 12.0; O, 16.0; Assuming that the experiment is carried out under room temperature and pressure, 1 mole of gas occupies 24000 cm3 under these conditions. [2]

River Valley High School 9647/02/PRELIM/11 [Turn over Preliminary Examination 2011 3 (c) Using the information given in (a) and (b), calculate the volume of the apparatus needed for the collection of CO2 gas in this experiment. [2] (d) With the help of your diagram in (a), describe the procedure to find the percentage mass of CaCO 3 in the rock sample. Your plan should give a step-by-step description of the method, including the calculations to determine the percentage by mass of CaCO3. [3] ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… (e) Suggest a possible error in the above experiment and propose how it can be minimised. [2] ………………………………………………………………………………………… ………………………………………………………………………………………… [Total: 12]

River Valley High School 9647/02/PRELIM/11 [Turn over Preliminary Examination 2011 4 2. N-Phenylethanamide, a drug once used to reduce fever, has the following structure: N H O N-Phenylethanamide N-Phenylethanamide may be synthesised by reacting phenylamine with an acid chloride prepared by the reaction of ethanoic acid with thionyl chloride. The procedure of the synthesis is as described below. Some data about the compounds involved in the synthesis are given in the table below. Compound Formula Density / g cm –3 Mr Glacial ethanoic acid CH 3COOH 1.05 60 Thionyl chloride SOCl2 0.94 119.1 Phenylamine C 6H5NH2 1.02 93 N-Phenylethanamide Given above 1.22 135 Preparation of impure N-phenylethanamide 1 Place 6 cm 3 of glacial ethanoic acid in a clean and dry 250 cm 3 round bottom flask. Place a dropping funnel in the neck of the flask. 2 Place 20 cm 3 of thionyl chloride in the dropping funnel and add the thionyl chloride gradually over the course of 10 minutes. Ensure that the reaction mixture is stirred well. 3 When all the thionyl chloride has been added, gently heat the reaction mixture for 20 minutes. 4 Cool the mixture to room temperature and replace the dropping funnel with a new one. Place 20 cm 3 of phenylamine in the new dropping funnel and add the amine gradually over the course of 10 minutes. Ensure that the reaction mixture is stirred well. 5 When all the phenylamine has been added, allow the mixture to stir for about 20 minutes.

River Valley High School 9647/02/PRELIM/11 [Turn over Preliminary Examination 2011 5 (a) The synthesis of N-phenylethanamide is a two-stage process, the first being the formation of an acid chloride and the second being the reaction between the acid chloride and phenylamine. Using structural formulae, write an equation for each of these stages. [2] Stage 1: Stage 2: (b) Glacial ethanoic acid (step 1) refers to a liquid sample of water-free ethanoic acid. Suggest why it is used over an aqueous solution of ethanoic acid. [1] ………………………………………………………………………………………… ………………………………………………………………………………………… The reaction mixture after step 5 contains N-phenylethanamide and excess phenylamine. Pure N-phenylethanamide can be obtained from the mixture through the sequence of steps described below. Data about the compounds involved in the purification process are given in the table below. Compound Density / g cm –3 Solubility in water Phenylamine 1.02 moderate N-phenylethanamide 1.22 insoluble Diethyl ether 0.71 partial Water 1.00  Purification of impure N-phenylethanamide 6 Pour the reaction mixture into a separating funnel and add about a third its volume of diethyl ether. 7 Add 15 cm3 of 5% HC l and 15 cm3 of saturated sodium chloride solution into the separating funnel. Shake the mixture and allow the two layers to separate. Discard the aqueous layer. 8 Repeat Step 7 for 2 to 3 times, discarding the aqueous layer each time. 9 Pour 15 cm 3 of 10% sodium hydrogen carbonate into the separating funnel and shake the mixture cautiously. Allow the two layers to separate then discard the aqueous layer. 10 Transfer the organic layer into a round bottom flask. Evaporate the diethyl ether off using a Rotary Film Evaporator to obtain pure N-phenylethanamide.

River Valley High School 9647/02/PRELIM/11 [Turn over Preliminary Examination 2011 6 (c) After diethyl ether was added to the impure N-phenylethanamide (step 6), the mixture is shaken with 5 % HC l and saturated sodium chloride solution and the two layers are allowed to separate (step 7). (i) Suggest why ethanol is not a good organic solvent for this separation technique. ……………………………………………………………………................... ................................................................................................................. (ii) Suggest why saturated sodium chloride solution was added (step 7). ……………………………………………………………………................... ................................................................................................................. (iii) In the diagram of the separating funnel below, draw the two layers that will be observed after step 7. Indicate the relative position of the two layers and state the organic species present in each layer. [4] (d) The organic layer is washed with 10% sodium hydrogen carbonate (step 9) before the ether solvent was evaporated off. (i) Write an equation to show how the impurity is removed in this step. …………………………………………………………………...……............. (ii) Besides shaking the separating funnel cautiously, s