OCR A Jun 2013 Paper 2 Q8 (with explained solutions) |

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OCR A Jun 2013 Paper 2 Q8

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8 Poly(propenenitrile) is used to make acrylic fibres for clothing. Poly(propenenitrile) is a polymer manufactured from propenenitrile. 20 CN propenenitrile (a) Draw a section showing two repeat units of poly(propenenitrile). (b) Explain why this manufacture of poly(propenenitrile) has a 100% atom economy.[1] [1]OCR 2013<br />
(c) Propenenitrile is manufactured from propene as shown in the equation. 21 C3H6(g) + NH3(g) + 1O2(g) CH2CHCN(g) + 3H2O(g) H = 540 kJ mol1 The conditions used are 450 C and 2.5 atmospheres in the presence of a catalyst. Describe and explain, using le Chateliers principle, the effect on the position of equilibrium of the following changes:a temperature above 450 C a pressure above 2.5 atmospheres the absence of a catalyst. In your answer you should link the effects you describe with your explanations.[5] Question 8 continues on page 22OCR 2013 Turn over<br />
(d) A factory is able to make 11.13 kg of propenenitrile from 220 mol of propene. Calculate the percentage yield of the reaction to form propenenitrile from propene. 22 (e) The chemical industry uses temperature and catalysts to control the rate of reactions. percentage yield =% [2] Using Boltzmann distribution diagrams, explain the effect on the rate of a reaction of:increasing the temperature adding a catalyst.OCR 2013<br />
23[7] [Total: 16] END OF QUESTION PAPEROCR 2013<br />

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F322/01 Question 8 (a) Answer CN CN (cid:57) Mark Scheme Marks (b) All the reactants are made into the desired product OR it is an addition reaction (cid:57) June 2013 Guidance ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) ALLOW two or more repeat units but has to be a whole number of repeat units ALLOW vertical bond to CN to any part of the CN End bonds MUST be shown as either dotted or normal line IGNORE brackets IGNORE n ALLOW there are no waste (products) OR there are no by- products OR only one product is made ALLOW an addition polymer is made DO NOT ALLOW all the products are useful IGNORE additional reaction 24<br />
F322/01 Mark Scheme June 2013 Question 8 (c) QWCLinking effect with explanation Answer (as temperature rises) position of equilibrium changes to minimise effect of temperature rise by absorbing energy OR (as pressure rises) position of equilibrium changes to minimise the pressure increase by reducing the pressure and making fewer gas molecules (cid:57) as temperature rises the position of equilibrium shifts to the left AND increase in pressure shifts the equilibrium to the left (cid:57) relates change with temperature to the (forward) reaction being exothermic OR reaction releases energy or heat OR reverse reaction is endothermic OR reverse reaction takes in heat or energy (cid:57) change with pressure because there are fewer moles of reactants OR more moles of products (cid:57) removing the catalyst does not change the position of equilibrium (cid:57) Marks Guidance ALLOW suitable alternatives for to the left eg moves to the reactant side OR towards C3H6(g) or NH3(g) or O2 OR moves in reverse direction IGNORE responses in terms of rate This mark is dependent on correct change in position of equilibrium Moves towards the endothermic direction is not sufficient ALLOW fewer molecules of reactant This mark is dependent on correct change in position of equilibrium ALLOW equilibrium does not move OR catalyst has no effect on the equilibrium 25<br />
F322/01 Question 8 (d) Mark Scheme June 2013 Answer FIRST, CHECK THE ANSWER ON ANSWER LINE IF answer = 95.5, award 2 marks. actual amount propenenitrile is 210 (mol) (cid:57) % yield = 95.454545 (cid:57) Marks Guidance IF there is an alternative answer, check to see if there is any ECF credit possible using working below ALLOW theoretical mass of propenenitrile = 11660 g OR 11.66 kg ALLOW 11700 OR 11.7kg ALLOW 95 up to calculator value of 95.454545 correctly rounded up ALLOW 95 up to calculator value of 95.128205 correctly rounded up if 11.7kg is used ALLOW ecf from wrong actual mass or actual amount DO NOT ALLOW ecf if percentage yield is above 100% 26<br />
F322/01 Mark Scheme June 2013 Question (e) Boltzmann distribution Answer Correct drawing of one Boltzmann distribution (could be temperature or catalyst) (cid:57) axes labelled (number of) molecules and energy (cid:57) Increasing the temperature Correct drawing of Boltzmann distribution at two different temperatures with higher and lower temperature clearly identified (cid:57) more molecules with energy above Ea (number of) molecules energy Ea higher temperature Marks Guidance Look at the first Boltzmann distribution on the paper: If it is the temperature one then both curves will have to be correct Boltzmann distributionmust start at origin and must not end up at 0 on y-axis ie must not touch x-axis ALLOW a slight inflexion in the Boltzmann curve ALLOW particles instead of molecules DO NOT ALLOW atoms instead of particles or molecules DO NOT ALLOW number of particles at activation energy DO NOT ALLOW enthalpy ONLY penalise the incorrect use of atoms (instead of molecules or particles) the first time it is seen Maximum of curve for higher temperature to right AND lower than maximum of lower temperature curve AND above lower temp line at higher energy as shown in diagram below Higher temperature line should intersect the lower temperature only once 27<br />
F322/01 Question Mark Scheme June 2013 Marks Answer Ea cat Ea energy (number of) molecules Adding a catalyst idea that activation energy is lowered with a catalyst (cid:57) Collision theory reaction is faster with catalyst AND when temperature is increased (cid:57) Greater proportion of molecules with energy above activation energy (with increased temperature or when catalyst is used ) (cid:57) more effective collisions OR more successful collisions (with increased temperature or when catalyst is used) (cid:57) extra molecules with energy above Ea Total 16 28 Guidance ALLOW Ec OR Ecat for activation energy of catalysed reaction ALLOW activation lowered shown on Boltzmann distribution diagram ALLOW more molecules with energy above activation energy OR more molecules that overcome the activation energy OR more molecules have enough energy to react ALLOW this marking point once either in terms of using a catalyst or increasing the temperature ALLOW this marking point once either in terms of using a catalyst or increasing the temperature ALLOW more collisions involving particles with energy above the activation energy More collisions per second is not sufficient<br />

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