IJC 2008 H2 Chemistry Prelim II Paper3

INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION 2 in preparation for General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on separate paper. Additional Materials: Writing Papers Graph Paper Data booklet 9746/03 09 September 2008 2 hours READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer 4 out of 5 questions. You are advised to show all working in calculations. You are reminded of the need for good English and clear presentation in your answers. You are reminded of the need for good handwriting. Your final answers should be in 3 significant figures. At the end of the examination, fasten all your work securely together. The number of marks is given in the brackets [ ] at the end of each question or part question. This document consists of 10 printed pages and 0 blank page. Innova Junior College [Turn over

2 Answer 4 out of 5 questions 1 The colours of various vanadium ions are given in the table below. Oxi van V IV III II dation Number of adiuim ions Colour Yellow Blue Gre Violet en (a) Use Eθ values from the Data Booklet, predict what colour changes will be observed when copper is added separately and in excess to ammonium vanadate(V), NH 4VO3(aq), acidified with dilute sulfuric( VI) acid. Write balanced equation(s) for the reaction(s) you predict will occur. [3] (b) Anhydrous copper sulfate, CuSO 4(s), is a white powder that readily dissolves in water. (i) Describe and explain using balanced equations, what is seen when CuSO 4(s) is stirred with water. (ii) Describe and explain the final colour change seen when an excess of NH 3(aq) is added to CuSO4(aq). [4] (c) Hot ethanolic KOH C 6H5CH2Cl C 7H8O + C6H5CH2OCH2CH3 F G H (i) Suggest an identity for compound G. (ii) The hydroxide ion and ethanol can take part in an acid-base reaction. Write an equation to represent this. (iii) Compound F undergo nucleophilic substitution reactions with different nucleophiles to form compound G and H respectively. Identify the two nucleophiles in the reactions. (iv) Suggest a simple chemical test by which compound F and bromobenzene can be distinguished from each other. [5] (d) Step I KCN heat with H 2SO4(aq) (CH3)2CHOH (CH 3)2CHBr K L In ethanol followed by ethanol, Conc H 2SO4 and heat (i) State the reagents and conditions needed for step I. (ii) Identify the compounds K and L in the above reactions. [3] © INNOVA 2008 9746/03 [Turn over

3 (e) A simple rechargeable battery may be constructed by dipping two lead electrodes into aqueous lead(II) nitrate and passing a current for a few minutes. During the process, lead( IV) oxide is deposited on one of the electrodes. When the power source is disconnected and a bulb is connected across the two electrodes, the bulb lights for a time as the cell discharges. (i) Use the electrode reactions in the Data Booklet to predict the two half- equations during the discharge. Hence, construct the overall equation for the reaction that occurs. Calculate the E θ cell for this reaction. (ii) In a lead-acid car battery, similar reactions take place but the electrolyte of dilute sulfuric acid causes the lead(II) ions to be precipitated as PbSO 4(s), which coats the electrode. The Eθ cell of this cell is +2.0 V. Explain the difference between this E θ cell and the one calculated in (i) by reference to the concentrations the relevant aqueous ions. [5] [Total:20] © INNOVA 2008 9746/03 [Turn over

4 2 Iodine is poorly soluble in water. However, it dissolves in solutions containing iodide ions as the soluble I3 – is formed. The iodide ions and iodine molecules are in equilibrium with I 3 - (aq) ions as follows: I2 (aq) + I– (aq) I3 – (aq) 0.080 mol of iodine and 0.058 mol of potassium iodide were dissolved in 500 cm 3 of water until equilibrium is reached. (a) Write the K c expression for the equilibrium above, stating its units. [1] (b) If 0.0425 mol of iodine is present at equilibrium, find the equilibrium constant of the equilibrium obtained. [3] (c) The aqueous solution in (b) is then shaken with 800 cm 3 of toluene (methylbenzene), and some of the iodine molecules present at equilibrium dissolves in the toluene layer. A special type of equilibrium constant know n as partition coefficient describes the way a solute is distributed between two immiscible solvents A and B. It is the proportion of the concentration of solute in the two immiscible solvents. Partition coefficient = [ ] [] solute in solvent A solute in solvent B organic aqueous After some time, it is found that the concentration of iodine in the toluene layer is 0.0525 mol dm-3. (i) Find the amount of iodine in the aqueous layer. (ii) Hence, calculate the partition coefficient for iodine distributed between a layer of toluene and a layer of water at this temperature. (iii) Comment on your answer in part (ii) based on the interactions between molecules of iodine with each other, and also with the solvent. [6] (d) Methanol can be synthesized from carbon monoxide and hydrogen as follows: Step 1: CH 4 (g) + H2O (g) O(g) + 3H 2 (g) C 0HΔ > Step 2: CO (g) + 2H2 (g) H 3OH (l) C 0HΔ < (i) Suggest, with reasons, what conditions of temperature and pressure should be used to obtain a high equilibrium yield of the methanol based on Step 2. (ii) Suggest an economic advantage of operating these two steps in reaction vessels close to each other in an industrial plant. [5] © INNOVA 2008 9746/03 [Turn over

5 (e) An inorganic iodine compound, phosphorous tri-iodide, PI 3, is unstable to be stored. Hence, it is often generated in situ from red phosphorous and iodine for its use in organic synthesis of products. (i) Draw the structural formula of the organic product formed when methanol reacts with red phosphorous and iodine in situ. (ii) In order to obtain the clean organic product in the reaction in (i), the products are often washed with sodium carbonate instead of sodium hydroxide. • Suggest one reason for the use of sodium carbonate in this step. • Explain why sodium hydroxide is not the preferred washing reagent. (iii) PI 3 and BI3 can react in a mole ratio of 1:1 to form an addition product. • Draw the structural formula of the addition product. • State the shape of the product about phosphorus atom. • Suggest the type of bond formed. [5] [Total:20] © INNOVA 2008 9746/03