2022 GMSS Chem Prelims P2

80 Candidate Name Class Index Number ___________________________________________________________ CHEMISTRY Paper 2 6092/02 Sec 4 Express Additional materials : Nil 1 hour 45 minutes 22 Aug 2022 READ THESE INSTRUCTIONS FIRST Write your name, index number and class on all the work you hand in. Write in dark blue or black pen. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions in the spaces provided. Section B Answer all three questions, the last question is in the form either/or. Write your answers in the spaces provided. At the end of the examination, hand in Section A and Section B together. The number of marks is given in brackets [ ] at the end of each question or part question. A copy of the Periodic Table is printed on page 24. For Examiner’s Use Section A /50 B9 /10 B10 / 10 B11 /10 Total This document consists of 24 printed pages. [Turn over Geylang Methodist School (Secondary) Preliminary Examination 2022

2 GMS(S)/Chem/P2/PRELIM/2022/4E Section A Answer all the questions in this section in the spaces provided. The total mark for this section is 50. A1 The following ionic equations represent some common reactions. A Ba2+ (aq) + SO42− (aq) → BaSO4 (s) B 2Cl− (aq) → Cl2 (g) + 2e− C Cr3+ (aq) + 3e− → Cr (s) D Cu2+ (aq) + 2OH− (aq) → Cu(OH)2 (s) E H+ (aq) + OH− (aq) → H2O (l) F 2I− (aq) + Br2 (aq) → I2 (aq) + 2Br− (aq) Use the letters A, B, C, D, E or F to answer the following questions. You may use the letters once, more than once or not at all. (a) Which equation shows a reaction that forms a white precipitate? ……………………………………………………………………………………….. [1] (b) Which equation shows only reduction? ………………………………………………………………………………………. [1] (c) Which equation shows the neutralisation of a dilute acid by an aqueous alkali? ………………………………………………………………………………………. [1] (d) Which equation shows a displacement reaction? ………………………………………………………………………………………. [1] [Total: 4]

3 GMS(S)/Chem/P2/PRELIM/2022/4E A2 A sample of black ink contains a mixture of red, blue and yellow dyes. Usually, the solvent used to separate the dyes in black ink is a mixture of ethanol and water. The coloured dyes have different R f values in solvents with different compositions of ethanol as shown in the graph below. (a) Using evidence from the graph, predict the colours of the separated spots observed when the solvent used consists of 40% ethanol in the mixture. ……………………………………………………………………………………. [1] (b) State the Rf value of blue dye on the chromatogram when the solvent is a mixture of 32 cm3 of ethanol and 168 cm3 of water. ……………………………………………………………………………………. [1]

4 GMS(S)/Chem/P2/PRELIM/2022/4E (c) Using evidence from the graph, explain why a pure solvent such as water is not suitable for the separation of the black ink using paper chromatography. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. …………………………………………………………………………………… [2] [Total: 4] A3 An unknown colourless solution, X, was spotted in the laboratory. Several tests were carried out as shown in the flow chart below: no visible reaction no visible reaction solution X add silver nitrate solution add dilute nitric acid add sodium hydroxide solution add excess ammonia solution white precipitate white precipitate in colourless solution add excess sodium hydroxide solution white precipitate dissolves white solid as residue filter add aluminium and warm colourless pungent gas, Y colourless solution, Z add dilute hydrochloric acid

5 GMS(S)/Chem/P2/PRELIM/2022/4E (a) (i) Identify gas Y. ……………………………………………………………………... [1] (ii) Describe a test to confirm the identity of Y. …………………………………………………………………………. …………………………………………………………………………. ……………………………………………………………………… [1] (b) Identify solution Z. ……………………………………………………………………………... [1] (c) Prior to the addition of silver nitrate solution, dilute nitric acid was added to unknown solution X. (i) Explain the purpose of adding dilute nitric acid. …………………………………………………………………………. …………………………………………………………………….. [1] (ii) What can be deduced from the “no visible reaction” as the observation, prior to adding the silver nitrate? ………………………………………………………………………….. ……………………………………………………………………… [1] [Total: 5]

6 GMS(S)/Chem/P2/PRELIM/2022/4E A4 The reaction between hydrazine and hydrogen peroxide is commonly used in rocket technology due to the rapid production of gases. The equation below shows the reaction between hydrazine and hydrogen peroxide. N2H4 (l) + 2H2O2 (aq) → N2 (g) + 4H2O (g) ∆H = -777 kJ (a) (i) Draw the dot and cross diagram of hydrazine, showing only the valence electrons. [2] (ii) Predict and explain in terms of bonding and structure the electrical conductivity of aqueous hydrogen peroxide. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………... ………………………………………………………………………………. [2] (b) (i) Explain, in terms of bond breaking and bond forming, why the reaction of hydrazine and hydrogen peroxide is exothermic. ………………………………………………………………………….............. …………………………………………………………………………............. …………………………………………………………………………............ …………………………………………………………………………........ [2]

7 GMS(S)/Chem/P2/PRELIM/2022/4E (ii) Table 4.1 shows the bond energies of various covalent bonds. Table 4.1 Using the information provided in Table 4.1 and the structural formula of H2O2 as shown here, calculate the bond energy of O−O, y. Structural formula of H2O2 [2] (c) In the reaction, 100 kg of hydrazine was used to react with 200 kg of hydrogen peroxide. Calculate the followings: (i) the number of mole in 100 kg of hydrazine; [1] (ii) the number of mole in 200 kg of hydrogen peroxide; [1] (iii) Identify the limiting reactant. ……………………………………………………………………………… [1] bond bond energy (kJ/mol) bond bond energy (kJ/mol) N−H 391 H - H 436 N - N 160 O - H 463 N = N 418 O - O y N ≡ N 941 O = O 496

8 GMS(S)/Chem/P2/PRELIM/2022/4E (iv) Hence, calculate the energy released when 100 kg of hydrazine is reacted with 200 kg of hydrogen peroxide. [1] [Total: 12] A5 Calcium nitrate reacts with sulfur under acidic condition to form sulfur dioxide, nitrogen monoxide and water. The ionic equation for the reaction is shown below. 4NO3 + 3S + 4H 3SO2 + 4NO + 2H2O (a) Identify the oxidising agent and reducing agent in the reaction. oxidising agent: ……………………………………………………… reducing agent: ……………………………………………………... [2] (b) Explain why the reaction is considered a redox reaction by referring to changes in oxidation states. ……………………………………………………………………..…………............... …………………………………………………………………..……………............... ………………………………………………………