Edexcel Jun 2014 Paper 2 Q21 (with explained solutions) |

Skip to content

Edexcel Jun 2014 Paper 2 Q21

Answers available below

21 This is a question about halogenoalkanes. (a) Halogenoalkanes can react with hydroxide ions in different ways depending on the conditions used. Using 1-chloro-1-fluoroethane, CH3CHClF, as an example of a halogenoalkane, the following reaction could occur in aqueous solution. CH3CHClF + OH (cid:111) CH3CHOHF + Cl (i) Suggest why it is unlikely that the fluorine atom in CH3CHClF would be substituted by the hydroxide ion. (1)*(ii) A student attempted to draw the reaction mechanism for the reaction in (a)(i), but made a total of three errors. Identify these errors and state how they should be corrected. (3) First errorSecond errorThird error14 *P42971A01424*<br />
(iii) In hot alcoholic solution, a different reaction may occur between halogenoalkanes and hydroxide ions. Write the equation for the reaction between 1-chloro-1-fluoroethane, CH3CHClF, and hydroxide ions in alcoholic solution. (b) Chloroethane can be produced in various ways as shown below. Identify, by name or formula, the reagent needed for each of these reactions. C2H6 (i)C2H5OH (ii)C2H5Cl (iii)C2H4 (c) (i) Chloroethane will react with alcoholic ammonia initially to produce ethylamine. Complete the equation for this reaction.+ NH3 (cid:111)+(ii) Name the type and mechanism of the reaction occurring in (c)(i). (2) (3) (1) (2)(iii) What feature of the ammonia molecule enables the reaction in (c)(i) to take place? (1)*P42971A01524* 15 Turn over<br />
(iv) If aqueous ammonia was used in (c)(i), instead of alcoholic ammonia, suggest the identity of the organic product that would be formed. (1)(d) Dichlorodifluoromethane, CCl2F2, is also known as Freon 12 and its manufacture was banned in 1994 under the terms of the Montreal Protocol. (i) Complete the equation for the initiation stage and suggest equations for two of the propagation stages and a termination stage for the mechanism of the reaction that this molecule might undergo with ozone. Initiation CCl2F2 (cid:111) Propagation 1 Propagation 2 Termination *(ii) Explain why the effect of Freon 12 molecules on the ozone layer was such a serious issue that scientists recommended its use to be discontinued. (4) (2)(iii) Freon 12, CCl2F2, could also be described as a greenhouse gas. Explain what the term greenhouse gas means. (2)16 *P42971A01624*<br />
(iv) Freon 12, and other similar molecules, are not normally viewed as contributors to the greenhouse effect. Suggest why this is so. (1)(Total for Question 21 = 23 marks) TOTAL FOR SECTION B = 39 MARKS *P42971A01724* 17 Turn over<br />

Show answer

Acceptable Answers Question Number 21 (a)(i) C-F bond is strong(er than C-Cl bond/C-OH bond) OR C-F bond is hard(er) to break (than C-Cl bond/C-OH bond) OR C-F bond enthalpy is high(er than C-Cl bond/C-OH bond) Ignore references to electronegativity Acceptable Answers Question Number 21 (a)(ii) The C-Cl dipole is the wrong way round (1) Allow reference to either only the carbon or only the chlorine having the wrong partial charge, e.g. the carbon should be + notThe arrow goes from the carbon to the (oxygen of the) hydroxide ion but should be the other way around OR The pair of electrons goes from the carbon to the (oxygen of the) hydroxide ion but should be the other way around (1) Use of the term carbocation means that only one of the first two marks may be awarded. The carbon bond to the hydroxy group should be to the oxygen and not to the hydrogen (1) Allow the above points to be drawn out correctly instead of stated in words Standalone marks IGNOREon fluorine atom Reference to lack of transition state Reference to absence of lone pair of electrons on the hydroxide ion Reject Mark H-F bond is strong Reject Mark C+ Cl OH group Hydroxide 6CH0201 1406<br />
Acceptable Answers Question Number 21 (a)(iii) CH3CHClF + OHCH2CHF + Cl + H2O Reject Mark CH3CF Organic product (1) Rest of equation correct (1) The organic molecules can be drawn displayed Allow any suitable metal hydroxide, e.g. CH3CHClF + NaOHCH2CHF + NaCl + H2O Allow C2H3F for the organic product Ignore state symbols even if incorrect. Question Number 21 (b) Acceptable Answers Reject Mark (i) (ii) Cl2/chlorine (gas) (1) PCl5/phosphorus (V) chloride (1) Allow Any other suitable reagents, such as HCl (and ZnCl2) OR NaCl + concentrated H2SO4 OR SOCl2 OR PCl3 OR (concentrated) hydrochloric acid for (ii) (iii) HCl/hydrogen chloride (1) Ignore Reaction conditions Cl2(aq)/Cl HCl(aq) 6CH0201 1406<br />
Question Number 21 (c)(i) Question Number 21 (c)(ii) Question Number 21 (c)(iii) Question Number 21 (c) (iv) Reject Mark C2H7N Acceptable Answers (+)Cl(-) CH3CH2Cl + NH3CH3CH2NH2 + HCl OR CH3CH2Cl + NH3CH3CH2NH3 OR CH3CH2Cl + NH3CH3CH2NH3 OR C2H5Cl + NH3C2H5NH2 + HCl OR CH3CH2Cl + 2NH3CH3CH2NH2 + NH4 OR C2H5Cl + 2NH3C2H5NH2 + NH4 (+) + Cl(-) (+)Cl(-) (+)Cl(-) Acceptable Answers Reject Mark Nucleophilic (1) Substitution (1) ALLOW Just SN2 for (1) Elimination Addition SN1 Acceptable Answers A lone pair (of electrons on the nitrogen atom)/ pair of non-bonding electrons Acceptable Answers Ethanol / C2H5OH / CH3CH2OH Reject Mark Pairs Just spare pair Reject Mark Alcohol 6CH0201 1406<br />
Question Number 21 (d)(i) Question Number 21 (d)(ii) Reject Mark Any charges Acceptable Answers Initiation CCl2F2CClF2+ Cl(1) -------------------------- ()+ O3CClF2O() + O2 (1) Propagation 1 This must include a free radical from the initiation step reacting with ozone Cl()+ O3ClO() + O2 OR CClF2 Propagation 2 ClO() + O()Cl() + O2 OR ClO() + O3Cl() + 2O2 (1) Allow propagation steps starting from CClF2 or either of the equations from propagation 1/CClF2O() ----------------------------------------+ ClCCl2F2 Termination Cl+ ClCl2 OR CClF2 OR ClO+ ClOCl2 + O2 (1) Allow other combinations of free radicals using those shown above. Ignore curly arrows Acceptable Answers The depleted ozone layer allows in (more) UV (radiation) (1) Which results in (skin) cancer/cataracts/mutation/ DNA damage/ Any reference to a chain reaction/ One Cl() destroys many ozone molecules/ Cl() is regenerated/ Cl() catalyst/ death of marine organisms such as phytoplankton (1) Standalone marks Any reference to greenhouse effect or global warming or infrared radiation scores (0) Reject Mark Cancer from Cl() 6CH0201 1406<br />
Question Number 21 (d)(iii) Question Number 21 (d)(iv) Acceptable Answers (A greenhouse gas) traps/absorbs/reflects AND Infrared (radiation)/heat/ longer wavelength radiation OR Stops infrared (radiation) /heat escaping (1) (Reflected/(Re)radiated/(Re)emitted) from the Earth(s surface) Allow Back to the earth (1) Mention of ozone layer depletion/acid rain max 1 Reject UV scores 0 overall. From the sun Acceptable Answers Reject Mark Mark Low concentration/amount/abundance in the atmosphere Short residency time Just they are no longer being used/they are not increasing. TOTAL FOR Q21 = 23 MARKS TOTAL FOR SECTION B = 39 MARKS 6CH0201 1406<br />

Question 17 18 19 20 21 22

About us | Need Help? | Feedback

Proudly powered by WordPress | Theme: Sydney by aThemes.