RVHS H2 Chem 2013 Prelim P3 QP

River Valley High School 9647/03/PRELIM/13 [Turn overPreliminary Examination 2013 RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9647/03 Paper 3 Free Response 16 September 2013 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. 1100

2 River Valley High School 9647/03/PRELIM/13 [Turn overPreliminary Examination 2013 Answer any four questions. 1 (a) Orthocaine, C 8H9O3N, is a local anaesthetic t hat causes temporary loss of pain. Orthocaine:  rapidly decolourises aqueous bromine to give A, C8H6O3NBr3.  gives a violet colouration on addition of neutral FeCl 3 (aq).  dissolves in NaOH(aq) to give B, NaC8H8O3N.  reacts with HCl (aq) to give a positively-charged ion C, C8H10O3N.  reacts in the presenc e of hot acidified KMnO 4(aq) to release a colourless gas that gives a white precipitate with limewater. Suggest the structures of orthocaine and A – C , explaining your reasoning. [9] (b) N2O, commonly known as laughing gas, is used in surgery and dentistry for its anaesthetic effect. Other than N 2O, other oxides of nitrogen include NO2 and NO. NO2 can be formed from NO as shown below: 2NO(g) + O2(g)  2NO2(g) Three experiments were carried out to find the relationships between the initial concentrati ons of NO and of O 2 and the initial rate of formation of NO2. Experiment Initial [NO] / mol dm3 Initial [O2] / mol dm3 Initial rate of formation of NO2 / mol dm3 s1 1 0.001 0.002 1.40  105 2 0.002 0.003 8.40  105 3 0.003 0.003 1.89  104 (i) Determine with reasoning, the order of reaction with respect to each of the reactants and the rate constant, k, stating its units. (ii) Calculate the initial rate of depletion of O 2 when [NO] = 0.002 mol dm3 and [O2] = 0.002 mol dm3. [5] 1101

3 River Valley High School 9647/03/PRELIM/13 [Turn overPreliminary Examination 2013 (c) NO2 can react with water to form nitric acid, HNO 3. Given that all the silver salts as shown below are spar ingly soluble in water, explain the following statement, using Le Chatelie r’s principle. Include equation(s) when possible. [3] (d) AgCl is a sparingly soluble salt and has a solubility value of 1.30 × 10 5 mol dm 3. To a 2.0 dm 3 of saturated solution of AgCl , 0.025 g of AgNO 3(s) was added. Calculate the mass of precipitate formed. [3] [Total: 20] AgCl & AgBr does not dissolve when nitric acid is added whereas CH3COOAg dissolves readily when nitric acid is added. 1102

4 River Valley High School 9647/03/PRELIM/13 [Turn overPreliminary Examination 2013 2 (a) Instant cold packs are a common dire ct replacement for crushed ice used as first aid on sports injuries. An instant cold pack consists of two bags; one containing water, placed inside another bag containing ammonium nitrate crystals, NH 4NO3(s). When the package is squeezed, the inner bag of water is broken and allowed to dissolve the ammonium nitrate. (i) Define the term enthalpy change of solution. (ii) Given that the enthalpy change of hydration of ammonium ions and nitrate ions are 132 kJ mol 1 and 207 kJ mol 1 respectively and the lattice ener gy of ammonium nitrate is 365 kJ mol1, construct an energy cycle and find the ΔHsoln of the reaction. (iii) In terms of structure and bonding, explain why ammonium nitrate gets cold spontaneously when dissolved in water. (iv) The entropies of NH 4NO3(s), ammonium and nitrate ions are given as such: Species S / J mol1 K1 Ammonium nitrate 151 Ammonium ions 186 Nitrate ions 256 Calculate the range of temperatur es that the instant cold pack will work. [7] (b) Solid ammonium nitrate is commonl y used to prepare nitrous oxide, N2O with water as a by-product via decomposition when heated. (i) Using the data provid ed below as well as your answer to a(ii), find the enthalpy change of reacti on for the production of nitrous oxide from ammonium nitrate. ∆Hf / kJ mol1 H2O (l) 285.8 HNO3 (aq) 174.1 N2O (g) +81.6 NH3 (aq) 80.8 NH3 (aq) + HNO3 (aq) → NH4NO3 (aq) ∆Hr = 57.0 kJ mol1 (ii) Draw the dot-and-cross diagram for nitrous oxide. [4] 1103

5 River Valley High School 9647/03/PRELIM/13 [Turn overPreliminary Examination 2013 (c) Nitrous oxide is used commercially as a mixture with oxygen gas and marketed as Entonox, which is a medical anesthesia gas used in normal childbirth. Endorphins are re leased upon inhalation of Entonox, producing a feeling of wellbeing. The structure of an endorphin, which is a peptide, is shown below. Under certain conditions, denaturation of a peptide can occur. (i) What is meant by the term denaturation? (ii) Suggest how pH changes can denature endorphins. (iii) How many different amino acid residues are present in an endorphin peptide structure? [4] (d) Another use of nitrous oxide is in the commercial preparation of sodium azide, NaN 3. Sodium azide is in turn used in air-bags put into automobiles. Upon severe impact, a detonator cap is ignited and causes sodium azide to decompose explosively according to the equation below and filling the air-bag: 2NaN 3(s) → Na(s) + 3N2(g) (i) Draw and name the shape of the azide ion, N3 . (ii) If 2.0 moles of NaN3 is detonated, what volume of gas is produced under standard conditions? (ii) A person driving a car with an ai r-bag system installed met with an accident at the top of the mountain wh ere the atmospheric pressure is 0.8 atm and the temperature is -10 °C. Will the air-bag containing 2.0 moles of NaN 3 inflate to the same volume as compared to the bag inflated under standard conditions? State any assumptions used in your evaluation. [5] [Total: 20] 1104

6 River Valley High School 9647/03/PRELIM/13 [Turn overPreliminary Examination 2013 3 Poly(tetrafluoroethene) is a polymer us ed as a coating in non-stick kitchen utensils and for replacement bone join ts. One of the stages in the manufacture of the polymer is Equilibrium 1: 2CHClF2(g)  C2F4(g) + 2HCl(g) The progress of this reaction was monitored by sampling method as described below. After a fixed concentration of CHClF2(g) is left to react in a sealed reactor at fixed temperature and pressure, 5.00 cm 3 of the resultant mixture is drawn at regular time interval. Each gas sample is quickly bubbled in 25.0 cm 3 of water and the solution formed is titrated with 0.100 mol dm3 NaOH solution. Three similar experiments were conducted in different conditions: Experiment [CHClF2(g)] / mol dm3 Temperature / K 1 1.00 373 2 1.00 423 3 0.500 423 The results of the three experiments are shown graphically. 15 20 25 30 35 40 45 Volume of NaOH(aq)/ cm3 Use these data where applicable in (a) and (b). Experiment 1 Experiment 3 Experiment 2 1105

7 River Valley High School 9647/03