MJC H2 Chem 2012 Prelim P2 QP

Calculator Model / No. Name ________________________ Class: ___________ Reg Number: ______ MERIDIAN JUNIOR COLLEGE Preliminary Examination Higher 2 ____________________________________________________________________________ Chemistry 9647 Paper 2 Structured Questions 10 September 2012 2 hours Additional Materials: Data Booklet ____________________________________________________________________________ INSTRUCTIONS TO CANDIDATES Write your name, class and register number in the spaces provided at the top of this page. Write your calculator brand and model/number in the box provided above. Answer all questions in the spaces provided on the question paper. All working must be shown clearly. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. You are reminded of the need for good English and clear presentation in your answers. FOR EXAMINER’S USE Q1 / 12 Q2 / 8 Q3 / 12 Q4 / 12 Q5 / 9 Q6 / 19 Total / 72 This document consists of 21 printed pages and 1 blank page. copyright chem dept @ meridian jc 1

copyright chem dept @ meridian jc 2 mass of solid in a saturated solutionsolubility = ×100mass of water in the saturated solution 1 Planning (P) (a) The ‘solubility’ of a substance in aqueous solution is defined as the mass of anhydrous solid that will dissolve in and just saturate 100 g of water at a fixed temperature. · A solution that is satur ated at a par ticular tempe rature is one in which no more solid may be dissolved. · A saturated solution can be recognised by undissolved solid in equilibrium with aqueous solution. · For example, a saturated solution of potassium chlor ate(V) can be represented by the equilibrium: KClO 3(s)  KClO3(aq) You are pr ovided with solid potassium chlo rate(V), KClO3, and distilled water. In addition to the standard apparatus present in a laboratory you are provided with the following materials: · evaporating basin · measuring cylinders (i) Use the information given above to plan an experiment to d escribe how you would prepare a saturated solution of potassium chlorate(V) at room temperature. ‘solubility’

copyright chem dept @ meridian jc 3 (ii) Hence, describe an experiment to determine the ‘ solubility’ of the potassium chlorate(V) prepared in (a)(i). (iii) Create specimen results for your experiment and show how you would use these results to calculate the ‘solubility’ of potassium chlorate(V) at room temperature. (iv) Identify a potential safety hazard in the experiment and state how you would minimise this risk. [7]

copyright chem dept @ meridian jc 4 (b) Sodium bromide crystallises as NaBr.2H 2O at low temperatures and as NaBr at higher temperatures. Temperature / oC 10 20 30 40 50 60 70 80 90 100 ‘Solubility’ of sodium bromide /g per 100g H2O 84.2 90.5 97.2 105.8 116.0 116.9 117.4 118.3 119.8 121.2 Plot the ‘solubility’ temperature data for sodium bromide and draw one line for the ‘solubility’ of NaBr.2H2O and another line for the ‘solubility’ of NaBr. Draw two separate lines and extrapolate them to a point of intersection. The line at higher temperatures represents the ‘ solubility’ of NaBr. The line at lower temperatures represents the ‘solubility’ of NaBr.2H2O. [2]

copyright chem dept @ meridian jc 5 (i) Read from the graph the temperature where the two lines intersect. This is the transition temperature. Estimated transition temperature = ______________________ (ii) Describe the difference in the variation of ‘solubility’ with temperature · above the transition temperature, · below the transition temperature. The ‘solubility’ curve represents equilibrium conditions between solid sodium bromide and dissolved sodium bromide. The position of equilibrium can be influenced by temperature change and whether a change is exothermic or endothermic. From the shape of your graph, comment on the likely enthalpy change for solid sodium bromide dissolving under equilibrium conditions. Explain your answer. [3] [Total: 12]

copyright chem dept @ meridian jc 6 R' R C O C + R' R O R' R C O C + O R' R + R O O R O O C 2 A ketene is an organic compound of the form RR'C=C=O. Ketenes can be prepared from acyl chlorides. base RR'CHCOCl RR'C=C=O + HCl (a) Suggest the type of reaction that might occur during the preparation of ketenes from acyl chlorides. [1] Ketene is a reactive compound which readily undergoes addition reaction, for example RR 'C=C=O + H2O ® RR'CHCOOH Ketenes also undergo cycloaddition reaction with unsaturated compounds to form four- membered or larger rings. The simplest ketene is ethenone, CH 2=C=O, where R and R' are hydrogen atoms. (b) (i) Describe the mechanism for the reaction between ethenone and water.

copyright chem dept @ meridian jc 7 (ii) E thenone reacts with ethanoic acid to give compound R, C4H6O3, which reacts with phenylamine to give compound S, C8H9NO. Compound S yields p henylamine and sodium ethanoate with hot aqueous sodium hydroxide. S uggest the structures of R and S. R S (iii) Compound T, an ester, is formed when two molecules of ethenone react with one molecule of hydrogen cyanide. 2CH 2=C=O + HCN ® C5H5NO2 T Suggest a structure for the compound T using the given information on the addition and cycloaddition reactions of ketenes. (iv) State the type of hybridisation and sketch the hybrid orbital s present at C-1 in ethenone. CH 2=C=O [7] [Total: 8] 1

copyright chem dept @ meridian jc 8 H C CH3 CH3 CH3 O H CH3 CH3 C CH3 3 a-Terpineol, C10H18O, contains an alcoholic group which is not easily oxidised. (a) Identify compounds A to E in the following reaction scheme. A B C D E [3] E D A B yellow ppt C C9H16O yellow ppt excess conc. H2SO4 170°C , H2, Ni, 10 atm H2, Ni, 10 atm warm alkaline aqueous iodine acidified KMnO4 heat warm alkaline aqueous iodine acidified KMnO4 heat HCl F a-terpineol

copyright chem dept @ meridian jc 9 (b) The conversion of a-terpineol to compound D uses HCl as the reagent. (i) Suggest how you prepare gaseous HCl in the laboratory using sodium chloride as one of the reactants. (ii) Explain, with aid of balanced equations, why small amounts of gaseous HI is produced when sodium iodide is used instead of sodium chloride in (b)(i). (iii) Gaseous H I can also be prepared by another two- step method. Firstly, iodine is directly