2015 HCI H1 Chemistry Prelims P2 Questions

1 HWA CHONG INSTITUTION Preliminary Examination Higher 1 CANDIDATE NAME CT GROUP 14S CHEMISTRY Paper 2 Candidates answer Section A on the Question Paper. Additional Materials: Data Booklet Writing paper 8872/02 2 Sept 2015 2 hours READ THESE INSTRUCTIONS FIRST Write your name and CT group on all the work you hand in. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue, correction fluid or tapes. Section A Answer all questions. Section B Answer two questions on separate answer paper. 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. FOR EXAMINERS’ USE ONLY Paper 1 Paper 2 TOTAL Multiple Choice Section A (Structured) Section B (Free Response) Q1 /18 Q4 / 20 Q2 /10 Q5 / 20 Q3 /12 Q6 / 20 / 30 Subtotal / 40 Subtotal / 40 This question booklet consists of 14 printed pages. 110

2 Section A Answer all the questions in this section in the spaces provided. 1 There is concern over the way the oceans are becoming more acidic as more carbon dioxide dissolves in them (a) (i) Draw a “dot-and –cross” diagram for carbon dioxide [1] (ii) Use your diagram to state and explain the shape and bond angle of a carbon dioxide molecule. ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ………………………………………………………………………………… [3] (iii) Carbon dioxide forms hydrogen bonds with water. Draw a diagram to illustrate this. [2] (iv) Carbon dioxide is not very soluble in water. Suggest an explanation for this in terms of hydrogen bonding. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………… [2]

3 (b) When carbon dioxide dissolves in water of the ocean, the following reactions occur. CO2(g)  CO2(aq) equation 1 CO2(aq) + H2O(l)  HCO3 r (aq) + H+(aq) equation 2 HCO3 r (aq)  H+(aq) + CO3 2r (aq) equation 3 (i) The reaction in equation 3 can reach a state of dynamic equilibrium. Explain what is meant by the term dynamic equilibrium. …………………………………………………………………………………… …………………………………………………………………………………… ……………………………………………………………………………………… [2] (ii) Suggest why the balance of CO 2(g) in the atmosphere and CO2(aq) in the oceans cannot be regarded as a dynamic equilibrium. …………………………………………………………………………………….. ………………………………………………………………………………………. [1] (iii) Explain why an increase in the concentration of dissolved carbon dioxide leads to an increase in the acidity of the water. …………………………………………………………………………………… ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (iv) The pH of the oceans is buffered by the reaction in equation 2. Explain the meaning of buffered. …………………………………………………………………………………… ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1]

4 (v) Give the important condition necessary for this equilibrium to result in buffering, in terms of concentration of species present. …………………………………………………………………………………….. …………………………………………………………………………………….. [1] (vi) Reference books states that the pH of the oceans has changed from 8.179 in pre-industrial times to 8.069 today. Calculate the percentage increase in [H +] % increase in [H +] = ………………………………………….[1] (c) The shells of some sea creatures are made of calcium carbonate. Use the equations below to explain a possible effect of increased acidity on the shells of these sea creatures. CaCO 3(s)  Ca2+(aq) + CO3 2r (aq) equation 4 CO3 2r (aq) + H+(aq)  HCO3 r (aq) equation 5 ……………………………………………………………………………………… ……………………………………………………………………………………… …………………………………………………………………………………….. [2] (d) The concentration of a saturated solution of carbon dioxide in water is 3.3 x 10-3 mol per 100 g at room temperature and pressure. 1.0 kg of this saturated solution is boiled, releasing all the CO2. Calculate the volume that this CO 2 would occupy at room temperature and pressure. One mole of gas at room temperature and pressure occupies 24 dm3. Volume of CO 2 : …………………………..………………... [1] Total [18]

5 2 (a) E300 is an oxidant used in white wines. The maximum allowed concentration of E300 in drinks is 150 mg dm r3. A student performed the following redox titration procedure to find out if a 250.0 cm3 sample of a drink containing E300 was within this limit. The sample was acidified followed by the addition of 25.0 cm 3 of 0.00500 mol dm-3 KIO3(aq). Excess KI(aq) was then added to form I2 in solution. IO3 r (aq) + 5I r (aq) + 6H+ (aq)  3I2(aq) + 3H2O(l) (i) Calculate the amount, in moles, of iodine, I2, formed in this reaction. [1] (ii) Some of the I 2 formed reacted with the E300 in the 250.0 cm3 sample of the drink. C6H8O6 + I2  C6H6O6 + 2H+ + 2I r E300 The amount of unreacted I 2 was found by titrating with sodium thiosulfate, Na2S2O3(aq), using starch indicator. At the end point, 20.4 cm3 of 0.00500 mol dm-3 Na2S2O3(aq), had been added. The following reaction occurred: I2(aq) + 2S2O3 2r (aq)  2I r (aq) + S4O6 2r (aq) Calculate the amount, in moles, of iodine, I2, remaining after the E300 had reacted. [1] (iii) Determine the concentration of the E300 in the 250.0 cm3 sample of the drink

6 and hence whether the drink is within the limit allowed. Mr ( E300) = 176 Concentration = ……………………… units = …………………. Is the drink within the allowed limit for E300? …………………… [3] (b) E300 has a C=C bond with two different groups on each carbon. It does not, however, show geometrical isomerism whereas 1,2-dichloroethene does. Explain why 1,2-dichloroethene shows geometrical isomerism and suggest a reason why E300 does not. …………………………………………………………………………………. …………………………………………………………………………………. ………………………………………………………………………………….. ……………………………………………………………………………………. ……………………………………………………………………………………. [3] (c) The primary alcohol group in E300 reacts with C17H35COOH to form another

7 antioxidant. (i) Draw the structural formula of the compound formed in this reaction. [1] (ii) What else must be added to a mixture of E300 and C 17H35COOH, to make the new antioxidant? ……………………………………………………………………………….. [1] Total [10] 3 1-methylcyclohexene is a naturally occurring hydrocarbon that can be used as a starting material to make other chemicals. (a) Draw a labeled diagram to show the orbitals that form the C=C bond in an alkene. [1] (b) When 1-methylcyclohexene is added to bromine in an inert organic solvent, there is

8 a fast reaction that decolourises the bromine. Suggest the structure of the organic compound formed. [1] (c) 1-methylcyclohexene also decolourises aqueous bromine. When water is present, a different organic compound with molecular formula C 7H13OBr can be formed. Suggest the structure of this organic compound. [1] (d) State the reagents and conditions needed to convert 1-methylcyclohexene into each of the three organic compounds shown below