YJC H2 CHEM P3

This question paper consists of 9 printed pages. YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE Parent’s Signature: CANDIDATE’S NAME: ______________________________ CTG: _________ YISHUN JUNIOR COLLEGE PRELIMINARY EXAMINATIONS 2009 CHEMISTRY 9746/03 HIGHER 2 MONDAY 24 AUGUST 2009 0800hrs − 1000hrs (2 hours) Additional materials: Writing papers and Data Booklet READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, name and CTG on all the work that 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 paper clips, highlighters, glue or correction fluid. Answer any four questions. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together.

2 Answer any four questions 1 (a) Sea squirts (Ascidia) have an extensive biochemistry based on vanadium, and some of them have blood containing vanadium compounds. The vanadium present exists in three oxidation states. Explain, by reference to the Data Booklet , why vanadium can form multiple oxidation states in its compounds whereas calcium does not form oxidation states greater than +2 in its compounds. [3] (b) Electrode potential values are given below for the reduction of oxygen to water and for the half-reactions which involve V 3+, VO 2+ and VO 2 +. These three ions are commonly found in aqueous solutions of vanadium compounds. These electrode potential values are obtained under standard conditions, except that pH = 7. Electrode potentials E / V VO2+(aq) + 2H+(aq) + e V3+(aq) + H2O(I) −0.50 VO2 +(aq) + 2H+(aq) + e VO2+(aq) +H2O(I) +0.16 O2(g) + 4H+(aq) + 4e 2H2O +0.98 (i) Draw a fully labelled diagram of the apparatus which could be used to measure the standard electrode potential of the VO2+/ V3+ electrode system. (ii) Predict, using the electrode potentials given above, the oxidation state of vanadium that would be stable in aqueous solution of pH = 7 in the presence of air. Explain how the data allow this prediction to be made. (iii) In reactions that occur in living cells, transition metal ions are often present in the form of biochemical complexes. Suggest why the electrode potential data given above do not allow reliable prediction to be made of the oxidation state of vanadium that would be stable in the presence of oxygen in such reactions. [7] (c) Explain why aqueous vanadium ( V) ion exists in the form of VO 3 − but not [V(H2O)6]5+. [2] (d) EDTA forms hexaco-ordinate complexes with many metal ions. The following table lists some of these complexes together with their stability constants. complex K stab [Ca(edta)]2− 5 x 1010 [Cd(edta)]2− 4 x 1016 [Zn(edta)]2- 3 x 1016 Structure of EDTA: C C H H N CH2 CH2C H H N CH 2 CH2 C C O O- O- OO C O O- O- Na+ Na+ Na+ Na+ 9746 / YJC / 2009 / Preliminary Examination / Paper 3

3 (i) Copy out the formula of EDTA and under line on your diagram the six atoms that form bond with the metal ions. (ii) Cadmium ions are poisonous as they can cause bone porosity by replacing the calcium ions in bones. One treatment for cadmium poisoning involves administering a solution of EDTA. Calcium and zinc are essential for health. Using the data given, explain how EDTA alleviates cadmium poisoning. Comment on a likely problem that might arise during the treatment, and suggest how the problem can be overcome. [4] (e) A useful commercial source of magnesium is seawater, where [Mg 2+(aq)] is 0.0540 moldm−3. The magnesium is precipitated from solution by adding calcium hydroxide. Mg2+(aq) + Ca(OH)2 (s)  Ca2+(aq) + Mg(OH)2(s) (i) Write an expression for the Ksp of Mg(OH)2, including its units. (ii) The numerical value for Ksp is 2.00 x 10−11. Calculate [Mg2+(aq)] in a saturated solution of Mg(OH)2. (iii) Hence calculate the maximum percentage of the original magnesium in the seawater that this method can extract. [4] [Total: 20] 2 (a) One of the compounds that contributes to the smell of roses, carnations, hyacinths and many more other flowers is Compound Y. It is widely used in perfumery, and it is the basis of all rose-smelling perfumes. Compound Y can be synthesised from phenylethanoic acid by the sequence of reactions shown below. C O OH CH2 C O OC2H5 CH2 Compound Y Reduction Na + C2H5OH Stage 1 (i) High resolution mass spectrometry shows that the accurate relative molecular mass of Compound Y is 122.08. Three possible molecular formulae for Compound Y, with relative molecular masses close to this value, are C7H6O2, C8H10O and C9H14. Accurate relative isotopic masses for the most abundant isotopes of carbon, hydrogen and oxygen are: 9746 / YJC / 2009 / Preliminary Examination / Paper 3

4 H = 1.008, C = 12.000, O = 15.995 Show how these isotopic masses can be used to determine which of the three possibilities is the molecular formula of Compound Y. (ii) State the reagents and conditions needed to carry out Stage 1 of the reaction sequence. (iii) It is thought that the sensation of smell is triggered by molecules which fit into smell receptors in the nose. There are probably several types of smell receptors, each type having a particular shape and containing particular chemical groups. The structures of three compounds, which have floral smells similar to Compound Y, are shown below. Suggest the common features possessed by the molecules of these three compounds that could be responsible for their similar smell. (iv) Using information in (a)(iii), together with your answer in (a)(i) suggest a structural formula for Compound Y. [6] (b) Suggest how each of the following multi-step transformation can be achieved. Indicate reagents and conditions you would use for each step, but do not give experimental details. (i) (ii) [6] CH3 COCl Br CH3CHO CO CH C O CHCH3CH3 O O 9746 / YJC / 2009 / Preliminary Examination / Paper 3

5 N H2 C (c) α-Te