IJC 2016 H2 CHEM P3 Teachers copy Prelims

INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION in preparation for General Certificate of Education Advanced Level Higher 2 CHEMISTRY Paper 3 Free Response Candidates answer on separate paper. Additional Materials: Writing Papers Data Booklet Cover Page 9647/03 26 August 2016 2 hours READ THESE INSTRUCTIONS FIRST Write your name and class 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 any four questions. Begin each question on a fresh sheet of paper. You are advised to show all working in calculations. You are reminded of the need for good English and clear presentation in your answers. You are reminded of the need for good handwriting. Your final answers should be in 3 significant figures. At the end of the examination, fasten all your work securely together. The number of marks is given in the brackets [ ] at the end of each question or part question. This document consists of 18 printed pages. Innova Junior College [Turn over TEACHER’S COPY

2 PRELIMINARY EXAM  INNOVA 9647/03/2016 [Turn over Answer any four questions. 1 Data concerning the elements of group II of the Periodic Table, at 298K, are given in the table. Further data may be found in the Data Booklet. M refers to elements of group II. 1st and 2nd IE of M / kJ mol-1 ΔHatom of M / kJ mol-1 ΔHhydration of M2+ / kJ mol-1 Eө/ V Ca 1740 178 –1650 –2.87 Sr 1608 164 –1480 –2.89 (a) The electrode reduction potential Eө of Group II elements gives an indication of the ease with which the following reaction occurs: M(s) M2+(aq) + 2e –– reaction 1 The enthalpy change of reaction 1 can be related to the following factors:  first and second ionisation energy of the element  enthalpy change of atomisation and  enthalpy change of hydration of its gaseous ion. (i) Construct an energy cycle relating the factors above, and use the values given above to calculate the enthalpy change of reaction 1 for calcium. [3] Cycle: all correct compounds with state symbols [2] (deduct 1m for omission of state symbols, Enthalpy change of reaction 1 = 178 + 1740 + (-1650) = +268 kJ mol-1 [1] (ii) By quoting appropriate data from Data Booklet, explain the difference in enthalpy change of hydration of calcium and strontium ions. [2] Ca2+ (0.099nm) has smaller ionic radius than Sr2+(0.113nm) -[1] Since they have the same charge, the charge density of Ca2+ is larger, Thus Ca2+ forms stronger ion-dipole interactions with water molecules [1] ΔHhydration of Ca2+ is more exothermic than that of Sr2+. ∆Hhydration(Ca 2+ ) Ca(s) Ca 2+ (aq) + 2e Ca(g) Enthalpy change of atomisation Ca + (g) + e - Ca 2+ (g) + 2e - 1 st ionisation energy 2 nd ionisation energy Reaction 1

3 PRELIMINARY EXAM  INNOVA 9647/03/2016 [Turn over (c) Calcium oxide is the key ingredient for the process of making cement. When calcium is burned in oxygen, calcium oxide is produced. When 1.50g calcium is burned in air, a mixture of ionic solids calcium oxide and red brown solid is formed. The red brown solid has the following composition by mass: Ca, 81.1%; N,18.9%. Adding water to the red brown solid produces calcium hydroxide an d 19.2 cm 3 of ammonia gas at room temperature and pressure. (i) Calculate the formula of the red brown solid. [1] Ca N Mass in 100g 81.1 18.9 Amt in 100g 2.0224 1.35 Simplest ratio 1.50 1 ratio 3 2 Empirical formula of solid: Ca3N2 (ii) Write an equation for the reaction between red brown solid with water. [1] Ca3N2 + 6H2O  2NH3 + 3Ca(OH)2 (iii) Write equations for the reactions of calcium with air and use them to calculate the mass of CaO formed when 1.5g of calcium is burnt in air. [3] Ca + ½O2  CaO 3Ca + N2  Ca3N2 2 equations correct : [1] No. of moles of ammonia produced = 19.2/24000 = 0.0008 No. of moles of Ca3N2 produced = 0.0008/2 = 0.0004 No. of moles of calcium used to react with nitrogen= 0.0004 x 3 = 0.0012 mass of CaO formed = (1.5/40.1 – 0.0012)(40.1+16) = 2.03g (d) Calcium oxide is normally made by heating calcium carbonate to a temperature above 825oC. A gas which turns lime water chalky is produced in the process. (i) Write an equation for the decomposition of CaCO3. [1] CaCO3(s)  CaO(s) + CO2(g) (ii) Explain why barium carbonate decomposes at a higher temperature than calcium carbonate. [2]  Ba2+ has larger cation size than Ca2+, thus has lower charge density. [1]  The polarising power of Ba 2+ is lower, thus less able to polarize electron cloud of carbonate anion, weakening covalent bonds (C—O) in the anion to a smaller extent [1]  More energy is needed to break down the anion and hence decomposition temperature for BaCO3 is higher.

4 PRELIMINARY EXAM  INNOVA 9647/03/2016 [Turn over (e) Methylcyclohexene reacts with hydrogen bromide to form alkyl bromides. + HBr C7H13Br methylcyclohexene (i) The above reaction could produce two isomers with molecular formula C 7H13Br. However, when the reaction is carried out, mainly one product is formed. Give the structural formula of the major product, explaining your answer. [2] H Br [1] Presence of an additional (more) electron donating alkyl group directly bonded to the positively charged carbon in H disperse the positive charge to a greater extent thus H is more stable , leading to the formation of the major product. [1] (ii) Describe the mechanism of the reaction between hydrogen bromide and methylcyclohexene, C6H9CH3. [3] Electrophilic addition [1] 2 marks for mechanism (penalise 1 mark for 1-2 errors, penalise 2 marks for 3 errors or more)  slow step and balanced equation  arrows and lone pair  polarity  correct intermediate Unsymmetrical dihalides reacts with alkene in a similar way as hydrogen halides. (iii) Predict the structure of the product when IBr reacts with methylcyclohexene, and explain your answer by considering the polarity within the molecule IBr. [2] Understanding that iodine is less EN than bromine: Iodine is less electronegative (or electron-deficient or electrophile) than bromine

5 PRELIMINARY EXAM  INNOVA 9647/03/2016 [Turn over [√] Thus, iodine will be added across the C=C first. [√] (or Brwill attack the carbocation formed) Thus, product is product [1] [Total: 20]

6 PRELIMINARY EXAM  INNOVA 9647/03/2016 [Turn over 2 Alcohols and carboxylic acids have many scientific, medical and industrial uses worldwide. (a) Methanol is made from the following gaseous reaction. CO(g)