Edexcel Jun 2011 Paper 2 Q19 (with explained solutions) |

Skip to content

Edexcel Jun 2011 Paper 2 Q19

Answers available below

PMT SECTION C Answer ALL the questions. Write your answers in the spaces provided. 19 This question is about nitrogen monoxide, NO, which can be described both as a friend and a foe. Chemists have discovered that nitrogen monoxide plays an important role in the body by dilating blood vessels. If someone is suffering from blood circulatory or heart problems, a chemical may be given which will quickly break down to give nitrogen monoxide. Years ago, nitroglycerine was used for this purpose. Interestingly, the same chemical Nobel had used to make dynamite was used to treat him in old age. In the laboratory, nitrogen monoxide can be prepared by adding concentrated nitric acid to powdered silver. Nitrogen monoxide is a colourless gas which is partially soluble in water. It is difficult to detect its smell, because it reacts with oxygen in the air to form pungent-smelling nitrogen dioxide. Nitrogen monoxide is formed when a mixture of air and oxygen is heated to a high temperature. This reaction occurs in the engines of cars and aeroplanes. Nitrogen monoxide has a disastrous effect on the ozone layer because it is a free radical. Nitrogen monoxide is also a greenhouse gas. (a) (i) What is meant by the term free radical? (1)(ii) Suggest a dot and cross diagram for nitrogen monoxide, showing outer shell electrons only, remembering that it is a free radical. (2) 16 *P38479A01620*<br />
PMT (b) (i) Part of the unbalanced equation for the preparation of nitrogen monoxide from nitric acid is shown below. Ag(s) + HNO3(aq)(cid:3)(cid:111)(cid:3)NO(g) + AgNO3(aq) Identify the elements which are oxidized and reduced and give their oxidation numbers. Element oxidizedOxidation number initialfinalElement reducedOxidation number initialfinal(ii) Complete and balance the equation for the reaction between silver and nitric acid. Ag(s) + HNO3(aq)(cid:3)(cid:111)(cid:3)NO(g) + AgNO3(aq) +(c) The reaction between nitrogen and oxygen to form nitrogen monoxide reaches equilibrium. N2(g) + O2(g) (cid:85)(cid:3)(cid:21)(cid:49)(cid:50)(cid:11)(cid:74)(cid:12)(cid:3)(cid:3)(cid:3)(cid:3)(cid:3)(cid:3)(cid:3)(cid:3)(cid:3)(cid:507)H (cid:57) = +180.4 kJ mol1 (i) Explain why the yield of nitrogen monoxide is increased when the temperature is increased. (3) (2) (1)*(ii) State and explain the effect, if any, on the yield of nitrogen monoxide when the pressure is increased. (2)*P38479A01720* 17 Turn over<br />
PMT (iii) State and explain how the rate of the reaction is affected by an increase in pressure. (2)*(d) (i) Explain why a jet aeroplane in flight causes much more damage to the ozone layer than cars carrying the same number of passengers at sea level. You should assume that the nitrogen monoxide outputs for both methods of conveying the passengers are the same. (2)18 *P38479A01820*<br />
PMT (ii) The reactions of chlorine free radicals with ozone may be represented by the following equations. (cid:38)(cid:79)(cid:135)(cid:3)(cid:14)(cid:3)(cid:50)3(cid:3)(cid:111)(cid:3)(cid:38)(cid:79)(cid:50)(cid:135)(cid:3)(cid:14)(cid:3)(cid:50)2 (cid:38)(cid:79)(cid:50)(cid:135)(cid:3)(cid:14)(cid:3)(cid:50)3(cid:3)(cid:111)(cid:3)(cid:38)(cid:79)(cid:135)(cid:3)(cid:14)(cid:3)(cid:21)(cid:50)2 Write corresponding equations for the reactions of the free radical nitrogen monoxide with ozone. Combine your two equations to show the overall reaction. Use these equations to explain why a small quantity of nitrogen monoxide can have a continuing effect on the ozone layer. (5) Equations Explanation(Total for Question 19 = 20 marks) TOTAL FOR SECTION C = 20 MARKS TOTAL FOR PAPER = 80 MARKS *P38479A01920* 19<br />

Show answer

Acceptable Answers An atom/ molecule (or ion)/species/entity with an unpaired electron Ignore any references to homolytic bond fission but penalise a reference to heterolytic bond fission Mark Mark Acceptable Answers Reject N single bond O Reject unpaired electron on oxygen Reject x x x NxODouble bond (1) Other electrons correct Dependent on double bond (1) Allow: all dots or all crosses or any combination Acceptable Answers Wherever it appears in the answer: Ag/silver (oxidized) 0 to +1/1+ (1) Wherever it appears in the answer: N/Nitrogen = +5/5+ (1) (Element reduced) N/nitrogento +2/2+ (1) N.B. Some candidates give +2/2+ and +5/5+ which is correct for both nitrogen products Only penalise no positive charges once Section C Question Number 19 (a)(i) Mark Reject Lone/single/free electron with unpaired electrons A free radical is an unpaired electron Question Number 19 (a)(ii) Question Number 19 (b)(i)<br />
Mark Mark Mark Reaction/equilibrium moves to the right/to oppose change without any other statement Reject Reference to atoms or ions instead of molecules Reject Acceptable Answers 3Ag(s) + 4HNO3(aq) (cid:74) NO(g) + 3AgNO3(aq) + 2H2O(l) 3Ag reacting to form NO and 3AgNO3 (1) 4HNO3 and 2H2O (1) mark independently of (b)(i) No TE from (b)(i) Acceptable Answers Reject Question Number *19 (b)(ii) Question Number 19 (c)(i) The reaction is endothermic (so goes to remove heat/lower the temperature) Allow H is positive (so goes to remove heat/lower the temperature) Question Number 19 (c)(ii) The yield is not changed Acceptable Answers OR No change OR no effect on the equilibrium (1) as there is no change in the number of (moles of) (gaseous) molecules OR as there is no change in the number of (gaseous) moles/particles (1) Allow: cylinder surface acts as catalyst (1) And all sites are filled so pressure has no affect (1) Second mark dependent on first in both cases Ignore any comment on rate whether correct or not<br />
Mark Mark Acceptable Answers Reject more particles per unit area Reference to atoms or ions instead of molecules Rate increases because (increase in pressure) means more particles per unit volume/less space for molecules/molecules closer together/greater or increased concentration (1) Comment: A correct statement of why the rate increases is needed with rate increases (somewhere in the answer) for the first mark which increases the frequency / increases the number of collisions/more chance of (successful) collisions (between molecules) (1) Ignore any references to (activation/kinetic) energy Mark independently Acceptable Answers Reject Jet aeroplanes fly (much) close(r)/near(er) to the ozone (layer)/ stratosphere (so more NO to deplete ozone layer) (1) ALLOW: Jet aeroplanes fly in the ozone (layer)/ stratosphere Some NO from cars reacts (e.g. with O2 to give NO2) OR NO from planes does not react before it can react with the ozone (1) Mark independently Anything else e.g. aeroplanes fly in the ionosphere NO absorbed by plants NO from cars dissociates/ decomposes/break down NO from planes does not dissociate/decompose/break down NO from cars takes a long time to reach the ozone layer NO dissolves Question Number 19 (c)(iii) Question Number *19 (d)(i)<br />
Mark Acceptable Answers Reject O3 (cid:74) O + O2 NO2 + O (cid:74) NO + O2 Comment: Please underline Key Points with highlighter, or annotate with tick at Key Point, or annotate with Key Point number from mark scheme wherever mark awarded. This ensures that it is easy to count up marks for this part. KP1 NO() + O3 (cid:74) ()NO2 + O2 (1) Comment: Dots are not required for KP1 KP2 NO2 + O3 (cid:74) NO + 2O2 (1) Comment: Dots can be on either side of both free radicals ALLOW for KP2: N.B. Both equations required here The overall equation is: KP3 2O3 (cid:74) 3O2 ALLOW: equilibrium arrow This mark is independent of KP1 and KP2 KP4 NO/the free radical (Allow Cl) is regenerated/a catalyst or wtte (1) KP5 and one molecule can break down large numbers of ozone molecules OR NO (Allow Cl) continues to react (with ozone)/reaction is continuous OR Mention of chain reaction (1) Ignore any reference to global warming as an additional problem KP4 and 5 marks are independent (1) Overall equation with nothing cancelled If Cl- is referred to as the radical then neither KP4 nor KP5 can be gained If the candidate makes clear that any of these processes lead to global warming loses KP4 or 5 but not both. TOTAL FOR SECTION C = 20 MARKS Question Number 19 (d)(ii)<br />

Question 17 18 19

About us | Need Help? | Feedback

Proudly powered by WordPress | Theme: Sydney by aThemes.