2019 TMJC H2 Chem Prelim P3 QP

Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry __________________________________________________________________________________ H2 CHEMISTRY 9729/03 Paper 3 Free Response 23 September 2019 2 hours Candidates answer on Answer Booklet. Additional Materials: Answer Booklet Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and civics group on all your work you hand in. Write in dark blue or black pen on both pages in the answer booklet. You may use an HB pencil for any diagrams, graphs or rough working. Do not use paper clips, glue or correction fluid. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. __________________________________________________________________________________ This document consists of 14 printed pages. TAMPINES MERIDIAN JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION

2 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry Section A Answer all the questions from this section. 1 Hydrocarbons, CxHy, are used extensively as sources of fuel in our modern day civilisation. (a) 10 cm3 of a gaseous hydrocarbon C5Hy was allowed to burn in an excess of oxygen at 300 ºC and 1 atm. In the reaction, there was an expansion of volume by 20 cm3. (i) Write a balanced equation, with state symbols, for the reaction at 300 ºC and 1 atm. [2] (ii) Determine the value of y. [2] Methane, CH4, is sometimes used in the production of hydrogen via a process known as steam reforming. CH4(g) + H2O(g) CO(g) + 3H2(g) (b) The steam reforming process is an endothermic reaction. (i) Using data from the Data Booklet , calculate a value for the enthalpy change of the forward reaction. [2] (ii) The actual value of the enthalpy change of reaction is found to be +206 kJ mol–1. Suggest a reason why your calculated answer in (i) differs from this value. [1] (c) At 600 K, t he value of the equilibrium constant, Kp, for the steam reforming reaction is 7.20 x 10–4. (i) Write the Kp expression for this reaction, giving its units. [2] (ii) Gaseous CH4, H2O and CO are introduced into a closed container at 600 K and their initial partial pressures are 1.20 atm, 2.10 atm and 1.80 atm respectively. Determine the partial pressure of H2 when equilibrium is reached. (You may assume that the extent of the forward reaction is small.) [3] (iii) Using information from (b), suggest how the temperature of the reaction can be changed so as to increase the yield of H2. Explain your answer. [2]

3 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry (d) Additional hydrogen can be recovered using the carbon monoxide produced in another reaction known as the water-gas shift reaction. CO(g) + H2O(g) CO2(g) + H2(g) (i) Name the type of hybridisation in the carbon atom in CO. Draw the hybrid orbitals around the carbon atom. [2] (ii) Given that the above reaction was conducted at 300 oC and 1 atm, calculate the volume of H2 that can be recovered from 5 kg of CO. [3] (iii) The volume of CO2 collected in the water-shift reaction should be the same as that of H2. However, the actual volume of CO2 collected was smaller. Suggest a reason why this is so. [1] [Total: 20]

4 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry 2 Propanoic acid, CH 3CH2COOH was initially known as propionic acid based on the Greek words, protos, meaning ‘first’ and pion, meaning ‘fat’. The pKa values of CH3CH2COOH and CH3CH(Cl)COOH are listed below. (a) (i) Explain why acid 2 has a lower pKa than acid 1. [2] (ii) Suggest a pKa value for acid 3. [1] (b) A 25.0 cm 3 solution of 0.10 mol dm –3 CH3CH2COOH was titrated against 0.20 mol dm–3 sodium hydroxide, NaOH. (i) Calculate the pH of the 0.10 mol dm–3 CH3CH2COOH. [1] (ii) Calculate the volume of NaOH required for complete neutralisation. [1] (iii) Write a suitable equation to explain why the pH at equivalence point is greater than 7. [1] (iv) Sketch the expected titration curve for this titration given that a total volume of 25.0 cm 3 of NaOH was added. On the titration curve, indicate the initial pH value and the equivalence volume. [2] (v) A buffer involving CH 3CH2COOH and its salt was formed during the progress of the titration. Circle the buffer region on the sketched curve in (iv) and indicate the corresponding pH value and volume at the maximum buffering capacity. [2] acid structural formula pKa 1 CH3CH2COOH 4.9 2 CH3CH(Cl)COOH 2.8 3 CH2(Cl)CH2COOH

5 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry There are many organic compounds such as amino acids and drug molecules that are derivatives of propanoic acid. (c) The starting material to synthesise 2-aminopropanoic acid, also known as alanine can be either pyruvic acid or ethanal. (i) The proposed synthesis for the deprotonated form of alanine from pyruvic acid is shown below. Suggest the reagents and conditions for steps 1, 2 and 3. [3] (ii) State the two types of reaction that had occurred in step 3 of the above proposed synthesis. [2] (iii) Write an equation to show how the zwitterion form of alanine can act as a buffer when a small amount of base is added. [1] (iv) The first step to synthesise alanine from ethanal is shown below. Explain whether ammonia can be considered as a Lewis base in the context of this synthesis. [1]

6 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry (d) Non-steroidal anti-inflammatory drugs are used for the relief of pain. One example is loxoprofen that is considered as a propanoic acid derivati ve based on its chemical structure. (i) Suggest a three-step synthesis of loxoprofen starting from compound E. compound E loxoprofen [4] (ii) Piketoprofen is produced by the reaction between an acyl chloride and a suitable organic compound. Suggest the structures of the acyl chloride and the organic compound. piketoprofen [1] (iii) The use of acyl chloride requires anhydrous conditions. Explain why acyl chloride undergoes hydrolysis more readily than chloroalkane. [2] [Total: 24]

7 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry 3 Cobalt is a transition element that plays an important role in hybrid electric vehicles and is also an essential part of vitamin B12. The common oxidation states of cobalt are +2 and +3. (a) Define transition element. [1] (b) Write the electronic configuration of cobalt(II) ion. [1] (c) State one physical characteristic property of transition elements that is different from the main group metals. Briefly explain why transition elements exhibit this property. [2] (d) The following sequence of reactions involving cobalt illustrates many of the characteristic properties of transition elements. (i) State the types of reaction occurring in steps I and II. [2] (ii) Suggest the formula of the cobalt-containing species G. [1] (iii) Cobalt is said to be a d-block element. The five degenerate orbitals in the 3d subshell are split into two energy levels in the presence of ligands in an octahedral environment as shown. Explain why the splitti