MI H2 Chem 2013 Prelim P3 QP

Class Adm No Candidate Name: This document consists of 11 printed pages and 1 blank page. [Turn over 2013 Preliminary Examination II Pre-university 3 H2 CHEMISTRY 9647/03 Paper 3 Free Response Friday, 20 Sep 2013 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet Graph Paper READ THESE INSTRUCTIONS FIRST Write your name, class and index number 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 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. Begin each question on a fresh sheet of paper. 837

2 Answer any four questions. 1. (a) State and explain in terms of electronic structure, two characteristic chemical properties of transition metals or their compounds. [4] (b) Transition element complexes such as those of iron are common reagents in colourful demonstrations of redox reactions. In one particular demonstration, the following observations were made. When aqueous iron( III) sulfate was added to aqueous sodium iodide, the reaction mixture turned brown. The brown colour is discharged upon addition of aqueous sodium hexacyanoferrate( II), Na4Fe(CN)6. On the other hand, when aqueous sodium hexacyanoferrate( III), Na3Fe(CN)6, was added to a fresh sample of the aqueous sodium iodide, the colour of the reaction mixture remained unchanged. (i) Explain the above observations using relevant data from the Data Booklet. (ii) Comment on the relative stability of the different oxidation states of iron in the presence of different ligands. [5] (c) Haemoglobin (Hb) is composed of 4 polypeptide chains: two alpha chains and two beta chains of polypeptides. Each chain contains one haem group, each of which contains one iron ion. The iron is the site of oxygen binding; each iron can bind one O 2 molecule thus each haemoglobin molecule is capable of binding a total of four O2 molecules. The iron–oxygen interaction is very weak; the two can easily be separated without damaging the haem unit or the oxygen molecule. The binding of an oxygen molecule to the iron in a haem unit is therefore completely reversible. (i) Explain how O 2 molecule binds to the Fe of the haem group. 838

[Turn over 3 1. (c) (ii) Each Hb molecule has a complex quaternary structure . Briefly describe what this means. (iii) A haemoglobin molecule in which the iron has separated from the oxygen molecule is called deoxyhaemoglobin. Blood containing red-bloo