RVHS Prelim P3 QP

RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION (II) CANDIDATE NAME CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9647/03 Paper 3 Free Response 18 September 2015 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 12 printed pages.

2 River Valley High School 9647/03/PRELIM/15 2015 Preliminary Examination II 1 (a) (i) Sketch the trend of the ionic radii of the ions for the third period of the Periodic Table, from Na to Cl. In your sketch, explain the general trend of ionic radii across the period. [4] (ii) Chlorides of aluminium and phosphorus both react readily with water to form acidic solutions. Write equations to illustrate these reactions. [2] (b) Chloric(I) acid, HC lO, is a common disinfecting agent used in swimming pools for its strong oxidising ability. Chloric(I) acid is a weak acid and ionises according to the equation: HClO(aq) ⇌ H+(aq) + ClO(aq) Ka = 3.50  108 mol dm3 (i) To a swimming pool treated with HClO, Ca(OH)2(s) was added to maintain a relatively constant pH of 7.6. Write an equation to show to illustrate the reaction between calcium hydroxide and chloric(I) acid [1] (ii) Given that 56 g of Ca(OH) 2 is added, and the swimming pool has a capacity of 2500 m3, calculate the following:  [ClO] [HClO]  initial [HClO] of the freshly treated swimming pool. [2] (c) (i) The level of chloride content in tap water can be quantified by obtaining the mass of lead required to precipitate lead(II) chloride. At 298K, the solubility of lead( II) chloride is 2.45  102 mol dm3. Calculate the solubility product of lead(II) chloride. [1] (ii) Given that the acceptable limit of chloride ions in tap water is 250 ppm, calculate the minimum mass of lead required for precipitation to occur in a 50 cm3 sample of tap water. You may ignore the low concentration of lead( II) ions originally found in tap water. (1 ppm = 1 mg per litre) [2]

3 River Valley High School 9647/03/PRELIM/15 [Turn over 2015 Preliminary Examination II (d) A compound M has a molecular formula of C 8H10O2, and gives purple colour with aqueous iron(III) chloride. When hot acidic potassium dichromate(VI) is added to M, the orange solution turn s green and compound N is formed . 1 mol of N reacts with 1 mol of phosphorus chloride to give compound P, which on further warming with sodium, produces a neutral compound Q that has a formula of C8H6O2. Suggest the structures of M, N, P and Q, and explain your reasoning. [8] [Total: 20]

4 River Valley High School 9647/03/PRELIM/15 2015 Preliminary Examination II 2. Nitrogen is a colo urless and odourless gas that makes up of about 78% of the Earth’s atmosphere. Many useful industrial products such as ammonia, nitric acid and organic nitrates incorporate nitrogen. However, conversion of free nitrogen to these useful products has proved to be an industrial challenge. (a) The production of many nitrogen compounds usually starts from the conversion of nitrogen to ammonia via the Haber process. N itrogen and hydrogen were placed in a 2.20 dm3 vessel containing iron powder. Temperature and pressure w ere maintained at 450 C and 2 0 atm respectively. Calculate the total number of moles of g as. You may assume that all gases behave ideally at the given condition. [1] (b) A 1 mol sample of NH 3(g) was extracted and placed in a 10 dm3 container. Pressure measurements were taken and compared against a sample of 1 mol of an ideal gas in an identical 10 dm3 container and the following data was obtained at two separate temperature: NH3 (450C) NH3 (25C) Ideal gas (450C) Ideal gas (25C) Pressure/atm 5.91 1.58 5.95 2.45 Suggest why pressure exerted by both ga ses are similar at 450 C but significantly different at 25 C. [2]

5 River Valley High School 9647/03/PRELIM/15 [Turn over 2015 Preliminary Examination II (c) Ammonium nitrate is a very soluble salt and is primarily used as a chemical fertiliser. Ammonia can be converted to ammonium nitrate in the following processes: Process 1: G aseous ammonia is oxidi sed in air at high temperature to form nitrogen(IV) oxide and steam. Process 2: This gaseous nitrogen( IV) oxide is then dissolved in water to produce nitric acid as well as nitrogen(II) oxide as the only by-product. Process 3: Nitric acid is then mixed with aqueous ammonia to form ammonium nitrate. The following data may be required for the subsequent questions: Compound ∆Hf /kJ mol1 NH3(g) 45 NH3(aq) 80.8 HNO3(aq) 207 H2O(l) 285 (i) Write balanced equation s including state symbols for process 1 and 2. [2] (ii) Given that process 2 mentioned in (c) is exothermic, suggest how temperature for this reaction should be controlled to maximize the yield of nitric acid. [2] (iii) Given that the enthalpy change of reaction between aqueous ammonia and nitric acid is 52.2 kJmol1, calculate a value for the enthalpy change of formation of aqueous ammonium nitrate by means of an energy cycle. [2] (d) Nitric acid is also used to manufacture nitrobenzene. Concentrated sulfuric acid is added as a catalyst. Describe the mechanism of this reaction. [3] (e) Nitrobenzene that is produced can be converted to phenylamine, which is considered as a weak base. State and comment on the relative base strength of phenylamine compared to ammonia. [2]

6 River Valley High School 9647/03/PRELIM/15 2015 Preliminary Examination II (f) The structure of protein can be classified into the primary, secondary, tertiary and quaternary structure. (i) Explain what is meant by a secondary structure of a protein [1] (ii) With an aid of a diagram, describe the bonding in a -pleated sheet. [3] (iii) Proteins are polymers made up of monomers of amino acids. One such amino acid is glutamic acid: The pKa values associated with this molecule is 2.10, 4.07 and 9.47. Propose the structure of glutamic acid at pH 7 and pH 3. [2] [Total: 20] CH C O OH NH2 CH2 CH2 C O OH

7 River Valley High School 9647/03/PRELIM/15 [Turn over 2015 Preliminary Examination II 3. (a) Cyanohydrins can be made by reacting ketones with an acidified solution of sodium cyanide. (CH3)2C=O + H+ + CN  (CH3)2C(OH)CN Kinetic studies were performed on the reaction by varying the concentration of reagents, and the following results were obtained. Expt No. [(CH3)2C=O] / mol dm3 [H+] / mol dm3 [CN] / mol dm3 Time / min 1 0.020 0.050 0.060 1.00 2 0.020 0.050 0.050 1.20 3 0.020 0.060 0.050 1.20 4 0.025 0.050 0.050 0.96 (i) Define the term order of reaction. [1] (ii) Determine the order of the reaction with respect to propanone, hydrogen ion and cyanide ion. Show your working in each case. [3] (iii) Hence, write down the rate equation for the reaction. [1] (iv) Describe the mechanism if the reaction is found to proceed via two steps. [2] (v) With the aid of a Maxwell -Boltzmann distribution curve, explain