7/29/2019 Extract Pages From 9701 s05 Ms 4

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Page 4 Mark Scheme Syllabus Paper

A LEVEL JUNE 2005 9701 4

University of Cambridge International Examinations 2005

5 (a) Ka = [RCO2-][H+]/[RCO2H] [1]

Part (a): [1]

(b) (i) The more chlorine atoms in the molecule, the stronger the acid, [1]

due to the electron-withdrawing (inductive) effect of Cl... [1]either...stabilising the anion, orspreading (-) charge more,or...weakening the O-H bond in the acid, or...increasing ionisation,orfacilitates H+ donation

orcausing the equilibrium RCO2H RCO2- + H+ to lie further to

the right.Mark is conditional on reference to the effect of presence ofchlorine. [1]

(ii) [H+] = (0.1 x 1.4 x 10-3) = 0.0118 (mol dm-3) allow 0.012 [1]

pH = -log10(0.0118) = 1.93 Allow 1.9 or 1.92 e.c.f. [1]

(iii) pKa = -log10(5.5 x 10-2) = 1.26 Allow 1.3 [1]

Part (b): [6]

(c) (i) Cl2(aq) AlCl3 or UV negates [1]

(ii) Electrophilic substitution oraddition-elimination [1]

Nucleophilic substitution orelectrophilic substitution on OH groupIf neither mark is awarded, could give salvage mark forsubstitution x2 [1]

(iii) Either: add Br2(aq) phenol decolourises it, or gives a white ppt.or: add FeCl3(aq) phenol give a purple colouror: add NaOH(aq) phenol dissolvesor: add UI solution phenol goes yellow/orange (A stays green)or: add diazoniumto solution in OH-

phenol gives orange/red colour(in each case, A give no reaction)

or: add Cr2O72-/H+/warm A changes colour from orange to green

or: add MnO4-

/H

+

/warm A changes from purple to colourlessor: add PCl5/POCl3/PCl3/SOCl2 A gives fumesor: add CH3CO2H + conc. H2SO4 A gives fruity smell

(in each case, no change with phenol)

Test + reagents [1] Both observations [1]

Part (c): [5]

Total: [12]

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7/29/2019 Extract Pages From 9701 s05 Ms 4

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Page 5 Mark Scheme Syllabus Paper

A LEVEL JUNE 2005 9701 4

University of Cambridge International Examinations 2005

6 (a) (i) Electrophilic substitution ornitration [1]

(ii) HNO3 + H2SO4 [1]

(both) conc., and at 50C T 60C [1]

(iii) NO2+ [1]

H NO2 H NO2

oretc.

Any on NO2 or H negates [1]

H+ [1]

Part (a): [6]

(b) (i) Reduction [1]

(ii) Sn/Fe/Zn/SnCl2 + HCl/H+/H2SO4 (but not conc. H2SO4)

orH2 + Ni/Pt (not LiAlH4) [1]

Part (b): [2]

(c) PCl5/PCll3/SOCll2/POCl3 (+ heat) aq negates [1]

Part (c): [1]

(d) (i) An amide, not peptide [1]

(ii) Heat with H3O+orheat with OH-(aq)

Orwarm (not heat/reflux) with aqueous amidase/peptidase/protease notenzyme/trypsin/chymotrysin/pepsin/papain etc. [1]

Part (d): [2]

Total: [11]

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