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CIE Jun 2015 v2 Paper 2 Q3
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![Ethane reacts with chlorine to form chloroethane. C2H6(g) + Cl 2(g)C2H5Cl (g) + HCl (g) (a) (i) Use bond energies from the Data Booklet to calculate the enthalpy change for this reaction. Include a sign in your answer. enthalpy change =kJ mol1 [3] (ii) State the conditions needed for this reaction to occur.[1] (iii) Use a series of equations to describe the mechanism of this reaction including the names of each stage and an indication of how butane can be produced as a minor by-product.[5] (b) Chloroethane can be converted back into ethane by a two-stage process via an intermediate compound, X. C2H5Cl reaction 1 reaction 2 C2H6 (i) Give the name of X.[1] (ii) Suggest the reagent and conditions needed for reaction 1.[2] (iii) Suggest the reagent and conditions needed for reaction 2.[1] [Total: 13]UCLES 2015 9701/22/M/J/15<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v2_QP_-_Paper_2_CIE_Chemistry_A-level_3.jpg)
![Page 3 Question Cambridge International AS/A LevelMay/June 2015 9701 22 Mark Scheme Syllabus Paper Mark Scheme Mark Total [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [18] [2] [2] [3] [3] [1] [2] [2] [1] [1] [1] [18] [1] [1] [1] [1] [3] [1] (a) (i) 2PbS + 3O2 2PbO + 2SO2 reagents and formulae balancing (ii) S (is oxidised) 2 to (+)4 O (is reduced) 0 to 2 (b) (i) T = 400600 C (chosen as a compromise because) High T increases rate ora High T decreases yield / moves eqm left / makes less SO3 as forward reaction exothermic ora (ii) High pressure increases rate as collision frequency increases ora High pressure moves eqm right / favours forward reaction as more moles on left ora Uneconomic to use high pressures / high yield at low pressure (c) (i) Reaction (too) exothermic / acid spray produced (ii) SO3 + H2SO4 H2S2O7 H2S2O7 + H2O 2H2SO4 (d) Preservative owtte antimicrobial / antioxidant / reducing agent (e) (i) 12.350.01 / 1000 = 1.23510 4 (ii) 1.23510 41000 / 50 = 2.4710 3 (iii) 2.4710 364.1 = 0.158327 g = 158 (3 sf only) (a) (i) Bond breaking = Cl-Cl = 242 C-H = 410 = 652 kJ Bond forming = C-Cl = 340 Enthalpy change = 652771 = 119 H-Cl = 431 = 771 kJ (ii) UV / High T / sunlightCambridge International Examinations 2015<br />
Page 4 Question (iii) Cambridge International AS/A LevelMay/June 2015 9701 22 Mark Scheme Syllabus Paper Mark Scheme Mark Total [1] [1] [1] [1] [1] [1] [1] [1] [1] [5] [1] [2] [1] [13] [1] [1] [1] [1] [4] [1+1] [2] [1] [1] [1] [1] [1] [3] [2] [11] Initiation Cl2 2Cl(cid:127) Propagation C2H6 + Cl(cid:127) (cid:127)C2H5 + HCl (cid:127)C2H5 + Cl2 C2H5Cl + Cl(cid:127) Termination (cid:127)C2H5 + (cid:127)C2H5 C4H10 All three names correctly assigned (b) (i) ethene (ii) KOH / NaOH ethanolic AND heat / reflux (iii) H2 AND Pt or Ni (catalyst) (a) (i) A = CH3CH2CH2CH2CHO B = CH3CH2CH(CH3)CHO C = (CH3)2CHCH2CHO D = (CH3)3CCHO (ii) CH3 CH3 CH3 CH2 H CH H H CH2 CH3 (b) (i) Fehlings / Benedicts OR Tollens OR dichromate OR manganate Warm / heat Fehlings / Benedicts =(Brick)-red ppt Tollens = silver / mirror OR grey/black precipitate Dichromate = orange to green with the aldehyde / A-D Manganate = purple to colourless (ii) (2,4-)DNP(H) / Bradys reagent Orange / yellow / red-orange / yellow-orange pptCambridge International Examinations 2015<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v2_MS_-_Paper_2_CIE_Chemistry_A-level_3-0.jpg)
