RVHS H2 CHEM P3 Prelim

River Valley High School 9647/03/PRELIM/11 [Turn overPreliminary Examination 2011 RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9647/03 Paper 3 Free Response 12 September 2011 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Graph Paper Cover Page Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class, Centre number and index number on all the work you hand in. Write in dark blue or black pen on both sides of 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. Begin each question on a fresh sheet of paper. A Data Booklet is provided. Do not write anything on it. 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, with the cover page on top. _______________________________________________________________________________ This document consists of 11 printed pages.

2 River Valley High School 9647/03/PRELIM/11 [Turn overPreliminary Examination 2011 Answer any four questions. 1 Nitrogen is one of the most abundant elements on earth. It is present in many molecules that find applications in chemistry and biology, such as ammonia, haemoglobin and amino acids. (a) During the combustion of ammonia, it reacts to form nitrogen gas and water vapour as seen in the equation below: 4NH3(g) + 3O2(g)  2N2(g) + 6H2O(g) (i) Using relevant data from the Data Booklet , calculate the enthalpy change of the reaction. (ii) Given that the theoretical value of enthalpy change of reaction is 1267 kJ mol-1, explain why the calculated value is different. (iii) State, with reason, the sign of the entropy change of the reaction. Hence, explain if the above reaction is spontaneous. (iv) Rank the four gases of NH 3, O 2, N 2 and H 2O in order of increasing deviation from ideal behaviour. Explain your answer. [8] (b) Haemoglobin is red pigment in blood responsible for carrying oxygen from the lungs to the cell of the body. The molecule consists of a Fe 2+ ion, a porphyrin ring system and a complex protein known as globin. The structure of haemoglobin is given below. (i) Describe the quaternary structure of haemoglobin. (ii) It was found that one molecule of haemoglobin combines with four molecules of oxygen. If 2.00 g of haemoglobin combines with 3.06 cm 3 of oxygen at 37.0 °C and 98.7 kPa, what is the molar mass of haemoglobin? State any assumptions you made in your calculations. (iii) The actual molar mass of haemoglobin is 6.90 x 10 4 g mol-1. Based on your working in (ii), suggest, with reasons, why there is a discrepancy in the two values. [6]

3 River Valley High School 9647/03/PRELIM/11 [Turn overPreliminary Examination 2011 (c) Amino acids are critical to life, and they serve as the building blocks of proteins. Out of the vast variety of amino acids, eight are termed as essential because they cannot be created by the human body, and therefore must be supplied in the diet. They are shown as follows: Amino acid R group Isoleucine (ile) CH(CH3)(CH2CH3) Leucine (leu) CH2CH(CH3)2 Lysine (lys) (CH2)4NH2 Methionine (met) CH2CH2SCH3 Phenylalanine (phe) CH2(C6H5) Threonine (thr) CH(OH)(CH3) Tryptophan (trp) CH2(C8H6N) Valine (val) CH(CH3)2 (i) Valine is able to exhibit stereoisomerism. State the type of stereoisomerism which occurs in valine and draw two structures which illustrate this isomerism. (ii) State and draw two types of side chain interactions that can occur between these eight essential amino acids. (iii) Draw the displayed formula of a tripeptide formed from one molecule of lysine, one molecule of threonine and one molecule of valine. [6] [Total: 20]

4 River Valley High School 9647/03/PRELIM/11 [Turn overPreliminary Examination 2011 2 Compound A, C 16H30O4, is believed to be an anti-cancer drug found in one medicinal plant extract in the jungles of Southeast Asia. On testing, it was found that: - Compound A is insoluble in both water and dilute aqueous HCl - Upon heating with dilute HC l, compound A gives two compounds: compound B, C 6H14O and compound C, C4H6O4. - Compound B can rotate the plane of polarised light and reaction of compound B with hot acidified potassium permanganate (VII) produces compound D, C 6H12O, which gives a yellow precipitate with iodine in aqueous sodium hydroxide. - Heating compound B over A l2O3 produces compound E, C 6H12, and vigorous oxidation of compound E produces butanoic acid as one of the products. - Compound C can be synthesised by reacting 1,2-diiodoethane with hot ethanolic NaCN followed by warming with dilute sulfuric acid. (a) Deduce the structures of compounds A, B, C, D and E. Explain the chemistry of the reactions described. [10] (b) Codeine is a drug used to treat mild to moderate pain and to relieve cough. The structure of codeine is as shown below. O O HO H N (i) Codeine has a tertiary amine functional group. Codeine can be sold in its ionic form of (R 3NH)+ Cl–, which is known as codeine hydrochloride. Calculate the pH of a solution when 0.10 mol of codeine hydrochloride is dissolved in 500 cm 3 of water. Kb of codeine = 1.62 × 10-6 mol dm-3 (ii) Calculate the pH of the resultant solution when 500 cm 3 of 0.20 mol dm -3 of NaOH is added to the codeine hydrochloride solution in (i). (iii) Using the answers in (i) and (ii), sketch a titration curve when 0.20 mol dm -3 of NaOH is added to 500 cm 3 of codeine hydrochloride solution in (i), showing clearly the pH at the point of maximum buffer capacity. [8]

5 River Valley High School 9647/03/PRELIM/11 [Turn overPreliminary Examination 2011 (c) One of the properties of an ideal drug is that the drug can be synthesised quickly with high yield. Using a Boltzmann distribution curve, explain how the use of catalyst can speed up the rate of reaction of synthesising a drug molecule. [2] [Total: 20]

6 River Valley High School 9647/03/PRELIM/11 [Turn overPreliminary Examination 2011 3 Ibuprofen belongs to a class of drugs called non-steroidal anti-inflammatory drugs (NSAIDs) used to reduce inflammation, pain and fever. Pain, fever, and inflammation are promoted by the release in the body of chemicals called prostaglandins. Ibuprofen blocks the enzyme that makes prostaglandins (cyclooxygenase), resulting in lower levels of prostaglandins. O OH ibuprofen The following diagram shows the first step in the synthesis route to form ibuprofen from compound A. (a) A series of experiments were carried out to find the effect of initial concentration of hydrogen ions, cyanide ions and A on the initial rate of formation of B. Experiment Initial concentration / mol dm3 Initial rate of formation of B / mol dm3 s1 [A] [H +] [CN] 1 0.020 0.060 0.060 1.00 2 0.020 0.050 0.050 0.833 3 0.020 0.050 0.060 1.00 4 0.025 0.050 0.050 1.042 (i) Write a balanced equation for the reaction that produces compound B.

7 River Valley High School 9647/03/PRELIM/11 [Turn overPreliminary Examination 2011 (ii) Use the data in the table to deduce the order of the reaction with respect to each of the three reactants, showing how you arrive at your answers. (iii) Write a rate equation for this reaction. (iv) Describe a mechanism that is consistent the rate equation deduced in (b)(ii), and indicate which step in the mechanism is the rate determining step. Explain your reasoning. [8] (b) Propose a 3-steps synthesis of ibuprofen starting from the compound 1-