DHS Prelim P2 Qn

This question paper consists of 21 printed pages and 1 blank page. © DHS 2017 [Turn over Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination 2017 Year 6 H2 CHEMISTRY 9729/02 Paper 2 (Structured) 11 Sep 2017 2 hours Additional Materials: Data Booklet INSTRUCTIONS TO CANDIDATES 1 Write your name, index number and class on this cover page. 2 Write in dark blue or black pen. 3 You may use an HB pencil for any diagrams or graphs. 4 Do not use staples, paper clips, glue or correction fluid. 5 Answer all questions in the spaces provided on the Question Paper. The number of marks is given in brackets [ ] at the end of each question or part question. You are advised to show all workings in calculations. You are reminded of the need for good English and clear presentation in your answers. For Examiner’s Use Question No. Section A Marks 1 13 2 13 3 20 4 14 5 15 Total 75

2 © DHS 2017 9729/02 [Turn over Answer all questions in the spaces provided. 1 The chalcogens, or the oxygen family, are the elements in group 16 of the Periodic Table. These elements are common in both organic and inorganic compounds. (a) The graph below shows the trend in the first ionisation energies of oxygen, sulfur and selenium. (i) Explain the trend in the first ionisation energies of oxygen, sulfur and selenium. [2] (ii) On the same grid above, sketch the trend in the first ionisation energies of nitrogen, phosphorus and arsenic. [1] 1st Ionisation Energy / kJ mol-1 Oxygen Sulfur Selenium

3 © DHS 2017 9729/02 [Turn over (b) A common chalcogen -containing reagent used in both organic and inorganic synthesis is hydrogen peroxide, H 2O2. Hydrogen peroxide readily decomposes at room temperature. However, this process is slow. Iodide ions, I–, catalyse this decomposition, as shown below: Step I: H2O2 + I – → H2O + IO– (slow) Step II: H2O2 + IO– → H2O + O2 + I – The overall equation for the decomposition of hydrogen peroxide is shown below: 2H2O2 → 2H2O + O2 The enthalpy and entropy changes for the reaction above are shown in the table below: Enthalpy change / kJ mol–1 –98 Entropy change / J K–1 mol–1 +71 (i) Using the data above, complete the diagram below to show the energy profile diagram for the decomposition of hydrogen peroxide in the presence of iodide ions. [2] Energy Progress of Reaction

4 © DHS 2017 9729/02 [Turn over (ii) An unknown amount of hydrogen peroxide was allowed to decompose in a 5 dm 3 closed vessel at 120 ºC. When all the hydrogen peroxide was decomposed, a pressure of 177 kPa was measured in the vessel. Determine the amount of hydrogen peroxide that decomposed in the vessel. (Assume that H 2O and O 2 are ideal gases under the above re action conditions) [2] (c) Chalcogens are also very commonly found in organic compounds. Table 1 below shows some common oxygen or sulfur containing organic functional groups. Oxygen- containing functional groups Alcohols R–OH Carboxylic acids O OH R Acyl chlorides O Cl R Sulfur- containing functional groups Thiols R–SH Sulfonic acids S O OHR O Sulfonyl chlorides S O ClR O Table 1 (i) Explain why carboxylic acids are generally more acidic than alcohols. [1]

5 © DHS 2017 9729/02 [Turn over (ii) Hence, suggest a reason why carboxylic acids are generally less acidic than their corresponding sulfonic acids. [1] (iii) A reaction scheme for the synthesis of dimethyl sulfide (CH 3SCH3) from methylsulfonyl chloride (CH3SO2Cl) is shown below: S O ClCH3 O S O OHCH3 O SHCH3 Step I KI Step II SCH3 CH3 1. Na 2. Reagent X Step III Given that sulfur -containing functional groups undergo similar reactions as their corresponding oxygen-containing functional groups (Table 1), suggest: I. The reagent(s) and condition(s) required for Step I. [1] II. The role of KI in Step II. [1] III. The identity of Reagent X in Step III. [1] IV. The structure of the product(s) formed when methylsulfonic acid (CH3SO3H) is reacted with ethylamine (CH 3CH2NH2) at room temperature. [1] [Total: 13]

6 © DHS 2017 9729/02 [Turn over 2 The electrolysis of dilute sulfuric acid was carried out using two different currents at room temperature and pressure. Current / A Duration / min Experiment 1 0.75 90 Experiment 2 0.45 90 Oxygen gas is collected at one of the electrodes. (a) (i) Calculate the final volume of oxygen produced in experiment 2. [2] (ii) The volume of oxygen collected for experiment 1 is shown below. On the graph above, draw a line to show each of the following: I. the volume of H 2 gas that would be given off in experiment 1 (Label this line 1) II. the volume of oxygen that would be produced in experiment 2 (Label this line 2) [2]

7 © DHS 2017 9729/02 [Turn over (b) In another experiment, electrolysis of aqueous potassium butanedioate, (OOCCH2CH2COO)K2, was carried out. It was found that two gases, Y and Z, were liberated at the anode in a 2:1 ratio by volume. Gas Y formed is absorbed by soda lime while gas Z is able to decolourise bromine water. (i) Suggest the identities of gases Y and Z. Gas Y is …………………. Gas Z is ……………………… [1] (ii) Construct the half-equation for the reaction that occurs at the anode and the cathode respectively. Anode ……………………………………………………………………… Cathode ………………………………………………………………………. [2] (iii) Predict the main organic product that would be obtained at the anode when a solution of potassium pentanedioate is electrolysed. [1]

8 © DHS 2017 9729/02 [Turn over (c) Nicotinamide adenine dinucleotide (NAD+) is involved in redox chemistry throughout the respiratory system. Aerobic respiration is the process of producing cellular energy involving oxygen. The electrode potential for the reduction of NAD + in a biological system, E(pH 7), at 1 mol dm–3, 25 oC and pH 7, is as shown. Its oxidised and reduced forms are represented as NAD+ and NADH respectively. NAD+ + H+ + 2e– NADH E(pH 7) = –0.320 V The reduction electrode potential of oxygen at different pH is given below. (i) With reference to the Data Booklet and the graph given above, calculate the value of Ecell for aerobic respiration. Write a balanced equation for this reaction. [3] 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 2 4 6 8 10 12 14 16 pH E/V

9 © DHS 2017 9729/02 [Turn over (ii) State how the Ecell will differ if the aerobic reaction is performed at a pH of 7.4. [1] (iii) Using your answer in (c)(i), calculate G(pH 7) for the aerobic respiration process. [1] [Total: 13]

10 © DHS 2017 9729/02 [Turn over 3 A coal-fired power station is fitted with a Flue Gas Desulfurisation (FGD) plant, which removes some of the sulfur dioxide from flue (waste) gases. I