HCI Prelim C2 P2 QP

This document consists of 19 printed pages. HWA CHONG INSTITUTION C2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 16S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper Additional Materials: Data Booklet 9729/02 11 September 2017 2 hours READ THESE INSTRUCTIONS FIRST Write your name, CT group, centre number and index number clearly in the spaces above. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided in the Question Paper. 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.          For Examiner’s Use 1 / 12 2 / 14 3 / 16 4 / 12 5 / 13 6 /8 Deductions Total / 75Calculator Model:

2   Hwa Chong Institution 2017 9729 / 02 / C2 Prelim 2017 1 (a) Atmospheric hydrogen and iodine, each 0.10 mol, are placed in a 2 dm 3 evacuated flask at 400 °C. After 30 minutes, the following equilibrium was established and the amount of H I was found to be 0.12 mol. H2 (g) + I2 (g) 2H I (g) (i) Write the expression for Kc and calculate its value at 400 °C. [2] (ii) At 40 minutes, the temperature of the system was raised to 600 °C and equilibrium was re-established at 60 minutes. Given that the K c at 600 °C was 0.36, show that the equilibrium concentrations of H 2, I2 and HI in the equilibrium mixture at 60 min are 0.0385 mol dm¯ 3, 0.0385 mol dm¯ 3 and 0.0231 mol dm¯3 respectively. [2]

3   Hwa Chong Institution 2017 9729 / 02 / C2 Prelim 2017 (iii) On the grid below, sketch the concentration versus time graphs for I2 and HI respectively under the conditions as described in (a)(i) and (a)(ii) from 0 to 70 minutes. Label the graphs and indicate significant values on the axes. [4] (iv) To find the amount of H I present at equilibrium at 30 minutes, the flask can be rapidly cooled and the H I is dissolved in water. The solution obtained can be titrated against NaOH(aq). Explain why the flask has to be rapidly cooled. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. [1]

4   Hwa Chong Institution 2017 9729 / 02 / C2 Prelim 2017 (b) When I2 combines with I¯, it forms the I3¯ ion which is responsible for the characteristic brown colour of aqueous I2. Draw a dot-and-cross diagram to show the bonding in I3¯. [1] (c) Explain, in terms of structure and bonding, why I 2 has a higher boiling point than HI. …………………………………………………………………………………………………….………. ………………………………………………………………………………………………….…………. …………………………………………………………………………………………….………………. ……………………………………………………………………………………….……………………. ………………………………………………………………………………………….…………………. [2] [Total: 12]

5   Hwa Chong Institution 2017 9729 / 02 / C2 Prelim 2017 2 (a) Metal ions, especially transition metal ions, possess the ability to form complexes with both organic and inorganic ligands. 1,10-phenanthroline (also known as ‘phen’) and ferrozine are organic ligands that can form complexes with Fe2+ ions.         (i) Explain the term ‘ligand’.     ………………………………………………………………………………………………………. ……………………………………………………………………………………………………….    [1]       (ii) In the following experiment, varying volumes of solutions of 0.1 mol dm –3 Fe2+ and 0.1 mol dm–3 phen are mixed to produce a complex of orange-red colour. xFe2+ + yphen → [Fex(phen)y]2+ The concentration of the orange-red complex formed is proportional to the absorbance of the solution which is measured using a colorimeter. The following graph is plotted using the results of the experiment. By drawing suitable lines on the graph, deduce the formula of the complex formed between Fe2+ and phen.      Formula of the complex ………………………………….      [2] 02468 1 0 Absorbance 10 8 6 4 2 0 2+ 3 FeV/ c m 3 phenV/ c m

6   Hwa Chong Institution 2017 9729 / 02 / C2 Prelim 2017    (iii)  Explain why the solution of the complex formed between Fe2+ and phen exhibits an orange- red colour.     ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ……………………………………………………………………………………………………….    [3]           (iv)  Ferrozine reacts with Fe 2+ in solutions to give a purple complex. Suggest why the colour of this complex is different from that formed with phen, by considering your answer to (iii).      ………………………………………………………………………………………………………. ……………………………………………………………………………………………………….      [1]          (b) Alkyl groups can be substituted into a benzene ring in the presence of a suitable catalyst. This is known as a Friedel-Crafts alkylation.       (i) Suggest a suitable reagent and condition to convert benzene to ethylbenzene. Reagent: …………………………………. Condition: ………………………………….    [1]       (ii) Name and outline the mechanism to convert benzene to ethylbenzene using the reagent and condition you proposed in (b)(i). Show all charges and use curly arrows to show the movement of electron pairs.    [3]

7   Hwa Chong Institution 2017 9729 / 02 / C2 Prelim 2017 (c)   Fermentation produces phenolic compounds that give wheat beer its distinctive spicy, clove-like flavor. This flavor comes from phenolic molecules such as vanillin and 4-VG.              (i)  Schiff bases are an important class of ligands that form complexes which can be used as antimicrobial agents. They are derived when a condensation reaction takes place between an amine and a carbonyl group. Vanillin can be used to synthesise the Schiff base ligand below. Give the structure of the molecule that reacted with vanillin to form this Schiff base ligand.       [1]       (ii) Suggest a simple chemical test to distinguish between vanillin and 4-VG. State the reagent and condition used and the expected observation for each compound.    ………………………………………………………………………………………………………. ……………………………………………………………………………………………………….    [2]       [Total: 14]

8   Hwa Chong Institution 2017 9729 / 02 / C2 Prelim 2017 3  Epoxides are a class of organic compounds with a three-membered ring structure containing two carbon atoms and one oxygen atom. The three-membered ring in epoxides makes them highly reactive and susceptible to “ring-opening reactions” whereby one of the C–O bonds breaks. Hence, epoxides are important precursors for many industrial and commercial applications. One such epoxide is styrene oxide.     (a) (i) State the hybridisation of the carbon atoms in the three-membered ring in styrene oxide, and the typical bond angle around a carbon atom with the same hybridisation. hybridisation: ………………………. typical bond angle: …………………    [2]      (ii)  The actual bond angle in the three-membered ring in styrene oxide is 60°. By comparing this bond angle with your answer in (a)(i), suggest why epoxides are susceptible to “ring- opening reactions”.    ………………………………………………………………………………………………………. ……………………………………………………………………………………………………….    [1]    (b)  An example of an epoxide ring-opening reaction is the hydrolysis of styrene oxide in the presence of a strong acid catalyst to form styrene glycol. To determine the reaction mechanism, isotopic labelling was used. The hydrolysis was carried out using “heavy-oxygen water”, H 218O. It is f