PJC H2 Chem 2013 Prelim P3 QP

© PJC 2013 9647/03/Prelim/13 [Turn over PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION HIGHER 2 CHEMISTRY 9647/03 Paper 3 Free-Response 23 September 2013 2 hours Candidates answer on separate paper. Additional Materials: Writing Papers Data Booklet Cover Page READ THESE INSTRUCTIONS FIRST Write your Centre number, index number and name on all 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 workings. 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. This document consists of 13 printed pages. Name: Index No.: CT Group: 12 999

2 © PJC 2013 9647/03/Prelim/13 [Turn over Answer any four questions. 1 (a) With the aid of a diagram, describe how a polypeptide chain is held in the shape of an alpha helix. [3] (b) Haemoglobin is the oxygen-carrying protein in red blood cells. (i) With reference to the haemoglobin molecule, describe and explain what is meant by the term quaternary structure of proteins. In your answer, you should state the type of bonding or interaction involved. (ii) A typical polypeptide chain of haemoglobin consists of 141 amino acids. The R groups of 3 of the amino acids are given below. amino acid formula of side chain (R in RCH(NH 2)CO2H) glutamic acid CH2CH2CH2CO2H valine CH(CH3)2 lysine CH2CH2CH2 CH2NH2 Use all three amino acids above to construct the displayed formula of a possible section of the polypeptide. (iii) Uncoiling of the protei n structure is favoured w hen temperature is higher than physiological conditions. With the aid of the equation, ∆G = ∆H – T∆S suggest why this process is favoured at higher temperatures. [ 8 ] (c) One molecule of haemoglobin can bi nd up to four molecules of oxygen, according to the following equation. Hb(aq) + 4O 2(aq) Hb(O 2)4(aq) Kc = 3 x 1020 mol-4 dm12 (i) Write an expression for K c for this reaction. (ii) Calculate the percentage of Hb(O 2)4 in an Hb-Hb(O 2)4 mixture when [O2] = 7.6 x 106 mol dm3. [3] 1000

3 © PJC 2013 9647/03/Prelim/13 [Turn over (d) (i) Carbon monoxide, CO, mainly causes adverse effects in humans by combining with haemoglobin to form carboxyhaemoglobin in the blood. This prevents haemoglobin from rel easing oxygen in tissues, effectively reducing the oxygen-carrying capacity of the blood. The equations below show the reac tions of haemoglobin wi