NYGH 2019-S3EOY-IP Chem P2

Class Register Number Name NANYANG GIRLS’ HIGH SCHOOL End-of-Year Examination 2019 Secondary Three CHEMISTRY Paper 2 Theory Paper 1 hour 45 minutes Monday 14 October 2019 1000 - 1145 Additional materials: Writing paper READ THESE INSTRUCTIONS FIRST Do not open this booklet until you are told to do so. Write your name, register number and class in the spaces at the top of this page and on any separate answer paper used. Section A (40 marks) Answer all questions. Write your answers in the spaces provided on the question paper. Section B (30 marks) Answer all questions including questions B7, B8 and B9 Either or B9 Or. Write your answers on the separate writing paper provided. At the end of the examination, 1. Fasten all your work securely together; 2. Circle B9 Either (for Either) or B9 Or (for Or) in the grid on the right to indicate the question you have answered; 3. Hand in Section A and Section B separately. INFORMATION FOR CANDIDATES The intended number of marks is given in the brackets [ ] at the end of each question or part question. You are advised to spend no longer than 60 minutes on Section A and no longer than 45 minutes on Section B. The use of approved scientific calculators is allowed. A copy of the periodic table is found on page 14. Paper 1 / 30 Paper 2 Section A / 40 B7 / 9 B8 / 11 B9 Either / B9 Or / 10 Total / 100 Setters: SCheong/ MI This document consists of 14 printed pages. NANYANG GIRLS’ HIGH SCHOOL [Turn over]

2019 End-of-Year Examination Secondary Three 2 Nanyang Girls’ High School Setters: SCheong/ MI Chemistry/ Paper 2 Section A (40 marks) Answer all questions. Write your answers in the spaces provided. A1 A barium meal, also known as upper gastrointestinal series is a procedure in which radiographs of the oesophagus, stomach and small intestine are taken after barium sulfate is ingested by 1 patient. Reacting barium hydroxide with sulfuric acid can produce barium sulfate. (a) Suggest a reason why barium sulfate is safe to be ingested and used as part of the procedure. [1] (b) The progress of the reaction between an impure solution of barium hydroxide and sulfuric acid can be followed by measuring the electrical conductivity of the barium hydroxide solution as shown in the setup below. 1cm3 of sulfuric acid is added at a time and after each addition, the conductivity was measured. The results obtained are shown in the graph below. (i) What volume of sulfuric acid is needed to neutralised 20cm 3 of impure barium hydroxide solution? [1] 0.35 mol dm–3 sulfuric acid 20 cm3 impure barium hydroxide solution conductivity measuring device stirrer volume of sulfuric acid added/cm3 electrical conductivity 0 2 4 6 8 10 12 14 16 18 20

2019 End-of-Year Examination Secondary Three 3 Nanyang Girls’ High School Setters: SCheong/ MI Chemistry/ Paper 2 [Turn Over] (ii) Barium hydroxide solution is formed by dissolving 25.0 g of impure sample of barium hydroxide in 1 dm3 of distilled water. Assuming that the impurities are not soluble in sulfuric acid, calculate the percentage purity of barium hydroxide sample. [3] (iii) In another experiment, water was accidentally spilled into the sulfuric acid solution. Would you expect a change in the volume of aqueous sulfuric acid required to neutralise the barium hydroxide solution ? Explain your answer. [1] (iv) Explain why barium hydroxide solution conducts electricity. [1] (v) Using your answer in (b)(iv), explain the shape of the graph. [3] Total [10]

2019 End-of-Year Examination Secondary Three 4 Nanyang Girls’ High School Setters: SCheong/ MI Chemistry/ Paper 2 A2 Trichloromethane, CHC l3, also known as chloroform, was used as an anaesthetic in surgery. It is not used today as it naturally reacts with oxygen in air to form a highly toxic gas phosgene, COCl2 and hydrogen chloride gas. (a) Write the balanced equation for the reaction of trichloromethane with oxygen. [1] (b) 10g of chloroform were reacted with excess oxygen and the gases formed were bubbled through aqueous ammonia and collected. Calculate the volume of gas collected. [2] (c) In phosgene, the carbon atom is in the centre of the molecule and is attached to both chlorine atoms and to the oxygen atom. (i) Draw a Lewis structure of the phosgene molecule. [1] (ii) State the number of sigma ( σ) bonds and the number of pi ( π) bonds present in a single phosgene molecule. [1] number of sigma bonds: number of pi bonds: (iii) Suggest the shape of the phosgene molecule and explain how you derive at your answer. [2]

2019 End-of-Year Examination Secondary Three 5 Nanyang Girls’ High School Setters: SCheong/ MI Chemistry/ Paper 2 [Turn Over] (iv) Explain why phosgene molecule is polar. [1] Total [8] A3 Reaction of an amine, C6H5NH2, with bromine produces hydrogen bromide. C6H5NH2 + 3Br2 C6H2NH2Br3 + 3HBr The table below shows the effect of concentration of each reactant on the rate of reaction measured by the concentration of hydrogen bromide formed per second. experiment no. concentration of C6H5NH2 / mol dm-3 concentration of Br2 / mol dm-3 initial rate of reaction / mol dm-3 s-1 1 0.001 0.001 0.007 2 0.001 0.002 0.014 3 0.001 0.003 0.021 4 0.002 0.001 (d) 5 0.002 0.003 0.084 (a) Describe the general relationship between the concentrations of the reactants and the rate of reaction. [1] (b) Using collision theory, explain your answer in (a). [2]

2019 End-of-Year Examination Secondary Three 6 Nanyang Girls’ High School Setters: SCheong/ MI Chemistry/ Paper 2 (c) Does the increase in concentration of C6H5NH2 and Br2 have an equal effect on the rate of reaction? Explain your answer using results from the table , stating clearly which experimental data you are using. [4] (d) Determine t he initial rate in experiment 4 and explain how you derive your answer. [2] Total [9] A4 Carbon nanotubes (CNT) is an allotrope of carbon that consists of two -dimensional hexagonal lattice of carbon atom s, bent and joined so as to form a hollow cylinder. The diagram below shows the structure of CNT. CNT can exhibit 200 times the strength of steel and an electrical conductivity 5 times that of the current capacity of copper. (a) With reference to the bonding and structure of CNT, determine why it is able to conduct electricity and has high strength. [3] carbon atom

2019 End-of-Year Examination Secondary Three 7 Nanyang Girls’ High School Setters: SCheong/ MI Chemistry/ Paper 2 [Turn Over] (b) State the electronic configuration of carbon, in spdf notation. [1] Total [4] A5 100% gold is called ’24 carat’ gold. The percentage of gold present in a gold alloy depends upon the carat value. carat value alloy 22 carat 91.6% Au, 5.6% Ag, 2.8% Cu 18 carat 75.0% Au, 12.5% Ag, 12.5% Cu 14 carat 58.5% Au, 20.5%Ag, 21.0% Cu 9 carat 37.5% Au, 31.25% Ag, 31.25% Cu An analyst was trying to determine the composition of a gold alloy comprising gold, silver and copper. He warmed 15 g of finely powdered alloy with excess concentrated nitric acid. This forms a suspension where copper and silv