2012 JJC H1 Prelim P2

1 Jurong Junior College 8872/02/Prelim 2012 [Turn over q JURONG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME CLASS EXAM INDEX NUMBER CHEMISTRY 8872/02 Paper 2 Structured Questions 27 August 2012 2 hours Candidates answer Section A on the Question Paper. Additional Materials: Answer Paper Data Booklet 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. Section A Answer all questions. Section B Answer two questions on separate answer paper. A Data Booklet is provided. Do not write anything on the Data Booklet. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A B6 B7 B8 Total This document consists of 14 printed pages.

2 Jurong Junior College 8872/02/Prelim 2012 [Turn over Section A Answer all questions in this section in the spaces provided. 1. (a) (i) On the following diagrams, plot points to show the variation in the named property of some Period 3 elements. Your points should indicate for each element, the relative position of first ionisation energy/ ionic radius with respect to other elements. The point for sulfur has already been plotted in each case. (ii) Briefly explain the following trends: the difference in first ionisation energy between phosphorus and sulfur. …...……………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… the trend in ionic radius from silicon to chlorine. …...……………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… [5] (b) (i) Describe what you would observe when a few drops of water is added to phosphorus(III) chloride, PCl3. Write an equation for this reaction. …………………………………………………………………………………… …………………………………………………………………………………… Ionic radius Si P S Cl first ionisation energy Si P S Cl

3 Jurong Junior College 8872/02/Prelim 2012 [Turn over 1. (b) (ii) When microwave radiation is passed through phosphorus( III) chloride, PCl3, at low pressure, a new chloride of phosphorus, A, is formed. A contains 69.6% by mass of chlorine and 30.4% by mass of phosphorus, and its Mr is 200. Calculate the empirical and molecular formulae of A. (iii) Assuming phosphorus and chlorine show their typical valencies, draw the displayed formula of A, showing all bonds and lone pairs. [5] [Total: 10]

4 Jurong Junior College 8872/02/Prelim 2012 [Turn over 2. (a) Ethanolamine is an organic base that is industrially important . The following table lists some of the properties of ethanolamine and propylamine. compound formula Mr boiling point/C solubility in water propylamine CH3CH2CH2NH2 59 48 fairly soluble ethanolamine HOCH2CH2NH2 61 170 very soluble (i) Suggest why the boiling point of ethanolamine is much higher than that of propylamine. …...……………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (ii) Draw a labelled diagram, showing lone pairs of electrons and dipoles, to illustrate why ethanolamine is very soluble in water. [2] (b) Write an equation to show how ethanolamine acts as a weak Bronsted base in water. …...……………………………………………………………………………………… [1] [Total: 3]

5 Jurong Junior College 8872/02/Prelim 2012 [Turn over 3. (a) Ketene, C2H2O, is a member of a class of unsaturated organic compounds that is widely used in pharmaceutical research for the synthesis of organic compounds. The structure of ketene is given below. The bonding in ketene may be described as a mixture of  and  bonding. The  bond between the carbon atom and the oxygen atom is shown in the following diagram. Complete the diagram to show orbital overlap that illustrates the  bonding between the carbon and oxygen atoms in a ketene molecule. [1] (b) Ketene burns completely in oxygen to form carbon dioxide and water. (i) Construct a balanced equation for the above reaction. …...………………………………………………………………………………. (ii) Define the term bond energy. …...……………………………………………………………………………… …………………………………………………………………………………… (iii) Use relevant bond energy values from the Data Booklet to calculate the enthalpy change of combustion of ketene. [4] [Total: 5] CH2 C O ketene C H C H O 

6 Jurong Junior College 8872/02/Prelim 2012 [Turn over 4. Blood plasma is a biological fluid that plays an important role in maintaining pH in the body. In the blood plasma, the equilibrium between carbonic acid, H 2CO3(aq), and hydrogencarbonate ion, HCO3−(aq), buffers pH changes. H2CO3(aq) = H+(aq) + HCO3−(aq) The Ka value for this equilibrium is 7.90  10−7 mol dm−3. At body temperature, the pH of the arterial blood plasma is 7.40. The concentration of H 2CO3(aq) in blood plasma is controlled by respiration through the lungs. H2CO3(aq) is in equilibrium with dissolved CO2(aq). H2CO3(aq) = CO2(aq) + H2O(l) In the lungs, excess dissolved CO2(aq) is exhaled as CO2(g). CO2(aq) = CO2(g) During heavy exercise, lactic acid , CH3CH(OH)COOH, is released into the blood and is buffered by the blood plasma. This eventually leads to an increase in the concentration of CO2(aq) and stimulates increased breathing. (a) (i) Explain what is meant by the term buffer solution. …...………………………………………………………………………………. ……………………………………………………………………………………. (ii) Write an expression for the acid dissociation constant, Ka, of H 2CO3(aq) and use it to calculate the mole ratio of HCO3– and H2CO3 in arterial blood plasma at body temperature. (iii) Hence, explain whether blood plasma has a greater capacity for absorbing H+ or OH– ions. …...………………………………………………………………………………. ……………………………………………………………………………………. (iv) Write an equation to show how blood plasma can buffer the pH change when lactic acid is released into the blood. …...……………………………………………………………………………….

7 Jurong Junior College 8872/02/Prelim 2012 [Turn over 4. (a) (v) By applying Le Chatelier’s principle, e xplain why the rate of breathing increases during the process of removing lactic acid. …...………………………………………………………………………………. …...………………………………………………………………………………. …...………………………………………………………………………………. …...………………………………………………………………………………. …...………………………………………………………………………………. …...………………………………………………………………………………. [8] (b) During exercise, lactic acid is produced in our muscles from pyruvic acid, CH3COCO2H. This reaction occurs in the presence of the enzyme lactic acid dehydrogenase. (i) Name the reaction that occurs when pyruvic acid is converted to lactic acid. …...………………………………………………………………………………. (ii) Suggest suitable reagents and conditions that can be used to convert pyruvic acid into lactic acid in a college laboratory. …...………………………………………………………………………………. (iii) How would you detect a small quantity of pyruvic acid in a sample of lactic acid? State the reagent(s) you would use and what would be seen in your test. …...………………………………………………………………………………. …...………………………………………………………………………………. …...………………………………………………………………………………. [4] [Total: 12]

8 Jurong Junior College 8872/02/Prelim 2012 [Turn over 5. Chloroacetophenone (compound F) was formerly the