SAJC Prelim P3 Qns

1   [Turn over NAME Class ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Chemistry (9729) Paper 3 Free Response 15 September 2017 2 hours Additional Materials: Data Booklet, Writing Paper READ THESE INSTRUCTIONS: Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Marks [60] Section B Answer one question. Marks [20] The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 14 printed pages (including this page).

2   [Turn over Section A Answer all the questions in this section. 1 (a) Iodine is a lustrous purple-black solid at standard conditions that sublimes readily to form a violet gas. (i) Give the equation that represents the second ionisation energy of iodine. [1] (ii) The graph below shows the second ioni sation energies of eight elements with consecutive atomic number. Which of the above elements, A to H, is iodine? Explain your answer.   [2] (iii) Explain the trend in second ioni sation energies from elements A to G, including the irregularity for element B. [4] (iv) Suggest, with reason, which of the above elements, A to H, can form an amphoteric oxide. Hence, write an equation to show the reaction of this amphoteric oxide with hydrochloric acid. (You are not requi red to provide the identity of the element in the equation.) [2] A B C D E F G H Second Ionisation energy/ kJ mol-1 Proton number

3   [Turn over 1 (b) Hydrogen peroxide reacts with acidified iodide ions to liberate iodine, according to the following equation: H2O2(aq) + 2H+(aq) + 2I(aq)  2H2O(l) + I2(aq) The rate of reaction can be measured by the increase in the concentration of iodine formed over time. The reaction was determined to be zero order with respect to [H+]. The following results were obtained by va rying the concentrations of hydrogen peroxide and iodide ions. Expt Initial [H 2O2(aq)] / mol dm-3 Initial [I(aq)] / mol dm-3 Initial rate / mol dm3 min1 1 0.020 0.040 1.2 x 10 -4 2 0.020 0.050 1.5 x 10 -4 3 0.050 0.040 3.0 x 10 -4 4 0.020 0.500 1.5 x 10 -3 5 0.050 1.000 7.5 x 10 -3 (i) What is understood by the terms order of reaction and half-life. [2] (ii) Determine the order of the reaction with respect to [H 2O2] and [ I] and hence suggest the units of the rate constant of this reaction. [3] (iii) The half-life of hydrogen peroxide in experiment 4 was 9. 24 min. Predict the half-life of hydrogen peroxide in experiment 5. [1] To investigate the rate of the above reaction, a t eacher suggested titrating the iodine formed with sodium thiosulfate solution at specified time intervals. (iv) Write an equation for the reaction between iodine and thiosulfate. [1]

4   [Turn over 1 (b) (v) Suggest how the reaction can be quenched at specified time intervals. [1] (vi) With reference to the Data Booklet, explain why hydrochloric acid is not a suitable acid used for the reaction between hydrogen peroxide and iodide. [2] [Total:19] 2 Metals have been used widely since ancient times. (a) An electrochemical cell is constructed using solutions of NaHSO4, H2SO3, and MnSO4 with suitable electrodes. The relevant half reactions are: HSO4–(aq) + 3H+(aq) + 2e– H2SO3(aq) + H2O Eo = +0.17 V Mn2+(aq) + 2e– Mn(s) Eo = –1.18 V (i) Draw a fully labelled diagram of the above electrochemical cell to measure the cell potential under standard conditions, indicating clearly the direction of the electron flow in the external circuit. [3] (ii) Write a balanced equation fo r the reaction that woul d take place if the electrodes of the cell were connected together by an external circuit. [1] (iii) Calculate the standard cell potential for this cell [1] (iv) Calculate the standard Gibbs free energy change, ∆Go, for the cell above. [1] (v) Suggest, with reasons, what happens to the Eocell when the following are done to the electrochemical cell above. 1) The pH of the HSO4–/H2SO3 half−cell is increased. 2) A solution of sodium hydroxide to the Mn2+/Mn half−cell.   [4]

5   [Turn over 2 (b) In an electrolytic cell, a current of 0.250 A is pa ssed through a concentrated solution of a chloride of iron, producing iron metal and gas, Y. (i) Write the equation for the half-reaction take occurs at the anode. [1] (ii) When the cell operates for 2 hours, 0. 521 g of iron is deposited at one of the electrodes. Determine the formula of the chloride of iron in the original solution. [2] (iii) Write a balanced equation for the overall reaction that occurs in the cell. [1] (iv) Calculate the current t hat would produce the gas Y from the solution at a rate of 2.50 g per hour. [2] (c) Metals are also used as catalysts in organic synthesis. The derivative of acetaminophene is investigated for the treatment of headaches. (i) A student suggested a flawed synt hesis of the derivative of acetaminophene starting from phenol. Identify and explain the error in each step. [3]

6   [Turn over 2 (c) (ii) Compound Z is an isomer of the derivative of acetaminophene. Suggest a simple chemical test to dist inguish between the derivative of acetaminophene and compound Z. [2] [Total:21] 3 (a) Blood obtains its colour from its respiratory proteins which occur as octahedral metal complexes. It is different in different organisms. Protein Source Metal per subunit De- oxygenated colour Oxygenated colour Haemoglobin Mammals, birds, fish, reptiles, insects 1 Fe red-purple red Haemocyanin mollusks, crustaceans, spiders 2 Cu colourless blue (i) Explain why oxygenated haemoglobin and haemocyanin are coloured. [3] (ii) Using the Cartesian axes, like t hose shown in Figure 3.1, draw fully labelled diagrams of the following. [2]

7   [Turn over  One of the d-orbitals at the lower energy le vel in an octahedral complex. Label the diagram “lower”.  One of the d-orbtials at the upper energy level in an octahdral complex. Label this diagram “upper”. Figure 3.1 (iii) Explain why the splitting of the d subshell occurs in an octahedral complex using your answer in (a)(ii). [2] y z x

8   [Turn over 3 (b) Oxygenated haemoglobin and haemocyanin were analysed and the absorption spectrum was observed. Colour Wavelength (nm) Colour Wavelength (nm) Violet 380 – 400 Yellow 560 – 580 Blue 400 – 490 Orange 580 – 620 Green 490 – 560 Red 620 – 800 (i) Which graph represents the absorpt ion spectrum of oxygenated haemocyanin? Explain your answer. [2] (ii) Which oxygenated blood (haemoglobin or haemocyanin) has a larger energy gap between the d subshells after splitting? Explain your answer. [2] (iii) The deoxygenated haemocyanin has a Cu+ central ion. State the electronic configuration of Cu+. Hence, suggest why the deoxygenated haemocyanin is colourless? [2]

9   [Turn over 3 (c) Carbon monoxide, chlorine and phosgene are the best known toxic gases. Many of these gases are assigned an NFPA 704 health rating of 4 (may be lethal) or 3 (may cause serious or permanent injury). Toxic Gas Chemical formula Colour Odour NFPA 704 Health Rating carbon monoxide CO colourless No 3 chlorine Cl2 green Yes 4 phosgene CCl2O colourless No 4