NYJC Prelim CHEM P2 ans

H2 Chemistry 9647/02 NYJC J2/16 PX [Turn over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME Teachers’ Mark Scheme CLASS 1 5 INDEX NO. TUTOR CHEMISTRY 9647/02 Paper 2 Structured 14 September 2016 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class 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 all questions in the spaces provided. A Data Booklet is provided. 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 1 P /12 2 / 15 /60 3 / 6 4 / 13 5 / 6 6 / 20 This document consists of 17 printed pages and 1 blank page.

2 H2 Chemistry 9647/02 NYJC J2/16 PX For Examiner's Use Answer all questions in the spaces provided. 1 Planning (P) Baker’s yeast is a useful enzyme which can be used to catalyse the decomposition of hydrogen peroxide. H2O2  H2O + ½ O2 You are provided with Set-up apparatus:  1 x retort stand with clamp  1 x 100 cm3 conical flask  1 x L-shape glass tube connector fitted with a rubber bung  1 x rubber tubing connection  1 x gas syringe (possible capacities of 10, 20 or 100 cm3) Reagents and apparatus  100 cm3 of yeast suspension  100 cm3 of 3% (by weight) hydrogen peroxide  Distilled water  Stopwatch  All other common laboratory equipment When 8.0 cm 3 of the yeast suspension, 4.0 cm 3 of H2O2 and 18.0 cm 3 of distilled water is mixed, 10 cm3 of oxygen gas was produced in 90 s. Use the above information and the reagents provided to design an experiment to  prove first order reaction with respect to yeast by a graphical method  prove first order reaction with respect to hydrogen peroxide by a graphical method In your experiment, you should perform 4 other experimental runs to mea sure the volume of oxygen gas produced at regular intervals. The volume of yeast suspension used should be varied in all the runs while keeping volume of H2O2 constant at 4.0 cm3. In your experiment, illustrate / describe the following:  A labelled set-up for your experiment using the set-up apparatus provided  Table of volumes that you will be using in your experiment  Calculations to determine the maximum volume of oxygen gas produced in each experimental run. In your calculations, assume that the density of H2O2 is 1.00 g cm 3 and conditions are at r.t.p.  Procedure for measuring the volume of oxygen gas produced at regular intervals and use the results to find the initial rate for each run graphically  Graphical analysis involving initial rates to deduce order with respect to yeast  Graphical analysis involving half-lives to deduce order with respect to H 2O2 based on one selected run

3 H2 Chemistry 9647/02 NYJC J2/16 PX [Turn over For Examiner's Use Experimental setup: 1 mark – 3 apparatus drawn and labelled correctly 1 mark – all apparatus drawn, labelled and connected correctly Table of volumes Run Vol of yeast /cm3 Vol of H2O2 /cm3 Vol of water /cm3 Total volume /cm3 1 4.0 4.00 22.0 30.0 2 6.0 4.00 20.0 30.0 3 8.0 4.00 18.0 30.0 4 10.0 4.00 16.0 30.0 5 12.0 4.00 14.0 30.0 1 mark – volume of yeast is between 2 – 20 cm3, volume of H2O2 is constant 1 mark – volume of water added accordingly to keep total volume constant Calculations to determine the maximum volume of oxygen gas produced in each experimental run Mass of 4.00 cm3 of H2O2 = 1.00 x 4.00 = 4.00 g Moles of H2O2 = (4.00 x 0.03) / 34.0 = 0.00353 mol [1] Moles of O2 gas = ½ (0.00353) = 0.00176 mol Volume of O2 gas = 0.00176 x 24000 = 42.4 cm3 [1] Hence minimum size of syringe to be used is the 100 cm 3 size if the reaction is allowed to go to completion

4 H2 Chemistry 9647/02 NYJC J2/16 PX For Examiner's Use Procedure for measuring the volume of oxygen gas produced at fixed intervals 1. Record the initial reading on the syringe 2. Using a burette, measure 2.0 cm3 of the yeast suspension and add into the conical flask 3. Using a measuring cylinder, measure 2 4.0 cm 3 of the distilled water and add into the conical flask. 4. Using a burette, measure 4.00 cm3 of the H2O2 into a small beaker. 5. Pour the H2O2 into the conical flask, stopper the conical flask with the conical flask and start the stop watch immediately. Swirl the conical flask a few times 6. Record the reading on the syringe every 10 seconds (or other regular time intervals, until 5 readings are collected i.e. 10 cm3 is produced. 7. Repeat steps 1 – 9 for the next 4 experimental runs, changing the volumes according to the table given. For run 5 (or any other run), make sure to use the 100 cm 3 syringe and allow the reaction to go to completion. 1 mark – 3/7 steps correctly written with appropriate apparatus used 1 mark – all steps correctly written with appropriate apparatus used Graphical analysis using the initial rates to deduce order with respect to yeast For the five set of readings, p lot the volume of O 2 produced against time. The tangent at time = 0 is the initial rate (see graph below) 1 mark Using the initial rates obtained, plot a graph of initial rates against volume of yeast used. If order is 1, a straight line through the origin should be obtained. 1 mark rate Volume of yeast Vol of O2 Time Tangent = initial rate

5 H2 Chemistry 9647/02 NYJC J2/16 PX [Turn over For Examiner's Use BLANK PAGE Graphical analysis using a half -life method to deduce order wit h respect to H 2O2 using the selected run Using the graph for run 5, find 2 consecutive half -lives. If order is one, the half -lives should be constant i.e. t1 = t2. [1] 1 mark – correct graph. X accepted instead of 42 but the graph must plateau. [Total: 12] Vol of O2 Time ½ (42) ¾ (42) 42 t1 t2

6 H2 Chemistry 9647/02 NYJC J2/16 PX For Examiner's Use 2 A solder is an alloy of metals which is used to join other metal pieces together. A specialist solder that can be used to join together pieces of aluminium is made from a mixture by mass of 65% zinc, 20% aluminium and 15% copper. An experim ental procedure can confirm the composition of a powdered sample of this solder, by adding reagents and then extracting from the mixture each of the following in sequence; (i) copper metal, (ii) aluminium as aluminium hydroxide, (iii) zinc as zinc hydroxide. You are provided with ● a sample of this solder, with approximate mass 4 g, ● 1.00 mol dm–3 sulfuric acid, ● 1.00 mol dm–3 ammonia. No other reagents should be used. Standard laboratory equipment is available. (a) Complete the flowchart below to show th e order in which the reagents would be added to the solder to allow you to extract and separate the components as copper metal, aluminium hydroxide and zinc hydroxide in Step 1, Step 2 and Step 3 respectively. [3] 6 points – 3 mks. Step 1 Step 2 Step 3 reagent(s) added H2SO4 reagent(s) added NH3 reagent(s) added H2SO4 substance(s) present in solution ZnSO4 Al2(SO4)3 substance(s) present in solution Zn(NH3)42+ (NH4)2SO4 – blank ok substance(s) present in solution (NH4)2SO4 – blank ok substance(s) removed by filtration (if any) Cu substance(s) removed by filtration (if any) Al(OH)3 substance(s) removed by filtration (if any) Zn(OH)2

7 H2 Chemistry 9647/02 NYJC J2/16 PX [Turn over For Examiner's