2019 RVHS Prelim P3 QP

River Valley High School 9729/03/PRELIM/19 [Turn over 2019 Preliminary Examination RIVER VALLEY HIGH SCHOOL JC2 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS 18J CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9729/03 Paper 3 Free Response 24 September 2019 2 hours Candidates answer on separate paper. Additional Materials: Answer Booklet 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. Section A Answer all questions. Section B Answer one question. Begin each question on a fresh page. 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. This document consists of 15 printed pages and 1 blank page. Section A

2 River Valley High School 9729/03/PRELIM/19 2019 Preliminary Examination Answer all the questions from this section. 1 (a) (i) Hydrogen halide, HX, is soluble in both polar and nonpolar solvents. Describe the interactions formed when HX dissolves in polar solvents such as water. [1] (ii) The boiling point s of the first four hydrogen halides down Group 17 are listed in the following table. Table 1.1 Hydrogen Halide Boiling Point / °C HF 20 HCl −85 HBr −67 HI −35 Describe and explain the trend. [2] (iii) Four gas jars containing a hydrogen halide from Table 1.1 were prepared. When a red-hot steel needle is introduced to the gas jars respectively, two of them showed intense colour changes while the other two showed no visible change. With reference to the Data Booklet, describe and explain the observations. [3] (b) (i) In an experiment, an excess of 5.00 g AgCl(s) was added to 1 dm3 solution of 0.00100 mol dm–3 NaCl and allowed to reach equilibrium at 298 K. The mixture was then filtered and the residue was dried thoroughly. 100 cm3 of the filtrate required the addition of 4.00  10–12 mol of NaBr for the first trace of AgBr to appear. Given that solubility of Ag Br in water is 0.140 mg L–1, calculate the concentration of Ag+ ions in the 100 cm3 filtrate. [2] (ii) Calculate the solubility of AgCl in mol dm–3. [2] (iii) Calculate the mass of residue collected from the filtration. [1]

3 River Valley High School 9729/03/PRELIM/19 [Turn over 2019 Preliminary Examination (c) (i) There are two possible intermediates for Reaction I. Draw the structure of the more stable intermediate and explain its stability. [2] (ii) Describe the mechanism of R eaction II to form Compound A. In your answer, use curly arrows to indicate the movement of electrons. [2] (iii) With reference to the hybridi sation of carbon atoms, explain why compound B is not a product from Reaction II. [2] [Total: 17]

4 River Valley High School 9729/03/PRELIM/19 2019 Preliminary Examination 2 (a) Phthalic anhydride is the acid anhydride of phthalic acid. It is an important industrial chemical for the synthesis of phthalic esters, which are used as plasticisers to soften plastics Phthalic anhydride (i) Given that phthalic anhydride reacts with an alcohol to form a monoester as the only product, write an equation for the reaction of phthalic anhydride with propan-1-ol. [1] (ii) The esterification of the monoester is more difficult to carry out and requires the removal of an inorganic by-product. Suggest the identity of the by-product. [1] (b) Hydrolysis of phthalic anhydride produce s phthalic acid, which is an aromatic dicarboxylic acid that can ionise in stages. Some information on phthalic acid and another aromatic acid are given below. Phthalic acid Table 2.1 pK1 pK2 Phthalic acid 2.89 5.51 Benzoic acid 4.20 - (i) Suggest a reason why the pK2 of phthalic acid is higher than its pK1. [1] (ii) Calculate the pH of a solution that is obtained after 50 cm 3 of 0.1 mol dm3 of NaOH is added to 10 cm3 of 0.2 mol dm3 phthalic acid. [2] (iii) Sketch the pH-volume added curve you would expect to obtain when 50 cm3 of 0.1 mol dm 3 of NaOH is added to 10 cm 3 of 0.2 mol dm 3 phthalic acid. Include relevant details from (ii) on your graph. [3] (iv) Predict the structure of the ionic compound that will be formed when sodium benzoate is added to phthalic acid. [1]

5 River Valley High School 9729/03/PRELIM/19 [Turn over 2019 Preliminary Examination (c) Kevlar is a heat resistant and strong synthetic polymer that is used in bullet-proof vests. Kevlar is synthesised in solution from the monomers of 1,4-phenylene-diamine and terephthaloyl chloride. 1,4-phenylene-diamine terephthaloyl chloride (i) State the type of reaction that occurs between 1,4-phenylene-diamine and terephthaloyl chloride that will result in the formation of a polymer. [1] (ii) A repeating unit is a part of a polymer whose repetition would produce the complete polymer chain (except the end groups) by linking the repeating units together successively along the chain. For example, the repeating unit of polyvinyl chloride is shown below. Draw the structure of the repeating unit of Kevlar. [1] (d) Polyprotic organic acids are usual precursors in synthesis. Suggest how the polyprotic organic acid below can be synthesised. Indicate reagents and conditions you would use in each step, including the structure of the intermediate(s), if any. [2]

6 River Valley High School 9729/03/PRELIM/19 2019 Preliminary Examination (e) Phthalic acid undergoes the reaction scheme below. Suggest the reagents and conditions for Reaction s A and B as well as the structure for Compound C. [3] (f) Compound D is a useful intermediate for making primary amines from bromoalkanes, by the following method. (i) State the types of reaction in Steps I, II and III. [3] (ii) Suggest reagents and conditions for Step III. [1] (iii) Draw a simple diagram to show how a water molecule can be attached to the anion in E. Label your diagram to show the dominant type of interaction involved. [1] (iv) When D undergoes combustion, a student, Eugene, predicted that one of the likely products is either NO or N 2 gas. He carried out a simple experiment to determine the combustion equation for D. First, he burnt 0.5 g of D in air. After combustion, he passed the gaseous mixture through potassium hydroxide and measured the volume of gas remaining at 30 ºC and 1 at m. Eugene determined that the gaseous volume was 42.26 cm3. Using the information above, determine the identity of the gas and write an equation for the combustion reaction of D. [3] [Total: 24]

7 River Valley High School 9729/03/PRELIM/19 [Turn over 2019 Preliminary Examination 3 Iron is the second most abundant metal in the earth’s crust and is abundantly used in building materials such as steel. The two most common oxidation states of iron in its compounds are +2 and +3. (a) When 5 cm3 of 0.2 mol dm3 iron(III) chloride solution was added to 10 cm3 of 0.6 mol dm3 sodium cyanide solution, the solution turned red. When the resultant solution undergoes a redox reaction, the solution turned yellow and the complex Y formed has a Mr of 211.8. Deduce, with the help of calculations and the Data Booklet, the formula e of the complexes formed when the solution turned red and yellow respectively. Write equations when appropriate. [2] (b) Explain the following observations regarding iron and its compounds. Support your answers wit