AJC Ans H1 chem prelim08

13 ANDERSON JUNIOR COLLEGE 2008 H1 Chemistry Paper 2 Section A 1 (a) Li(g) → Li +(g) + e (b) (i) 519; 494; 418 (ii) Down the group, first IE decreases because increase in shielding effect outweighs increase in nuclear charge Attraction between nucleus and valence electron decreases. (c) (i) Na +H93is3ionic 3compound3whereas3HF3is3simple3covalent 3molecule3 because3difference3in3electronegativity3between3atoms3is3high3in3NaH3 and3low3in3HF3 (ii) Na + H - NaH H F HF 2 (a) (i) Substitution;33with3catalyst3Fe3or3FeBr 333 (ii) Heat with acidified KMnO 4; methybenzene decolourises purple KMnO 4; benzene no change; C 6H5CH 33+333[O]3 /barb2right3C 6H5CO 2H3+3H 2O (b) (i) C6H63+33O 23/barb2right33C+33CO3+33H 2O3 (ii) ∆Hc(C 6H6) = -3276 kJ3mol 913 ∆Hf3 =36(–393)3+33(9286)393(393276)3=3+3603kJ3mol 913 3 (iii) methylbenzene is at a lower energy level than benzene; methylbenzene more stable than benzene (c) unburnt hydrocarbons; carbon monoxide H C7H8(l) C6H6(l) +60 3 0 +553 elements C & H2

23 3 (a) (i) [3H +3 ]3=3=30.023mol3dm –33 333 pH3=3–log 10 [3H +3]3=3–log 10 (0.02)3=31.70 (ii) The3acid3is3so3dilute3that3H +3from3dissociation3of3H 2O3cannot3be3ignored.33 [3H +3]3=31.03x310 –83+31.03x310 –73=31.13x310 –73mol3dm –333⇒3pH3=36.96 (b) A acids are H2SO 43and3H 2NO 3 +333 333stronger3acid3is3H 2SO 433 High K c ⇒ eqm lies to the right; tendency for H2SO 43to3lose3H +3is3higher B acids are CH 3CONH 23and3NH 4 +333 3stronger3acid3is3NH 4 +3 Low K c ⇒ eqm lies to the left; tendency for NH 4 + to3lose3H +3is3higher (c) (i) NaCl pH 7 ; Al 2Cl 633pH3339343;33SiCl 433pH32 (ii) NaC l3merely3dissolves3to3give3Na +3(aq)3and3C l–3(aq);3 3 Al 2Cl 63undergoes3partial3hydrolysis3 Al 2Cl 633+33aq3 →323 Al 3+ (aq)33+336Cl 9(aq)3 [Al(H 2O) 6]3+ 333 ⇔33[Al(H 2O) 5(OH)] 2+ 33+33H +3;3 3 SiC l43undergoes3strong3hydrolysis.3 SiCl 433+332H 2O33 /barb2right33SiO 233+334HCl 4 (a) (i) 83CO3+3173H23→3C 8H18 3+383H2O (ii) ∆H3=3[8(1074)3+317(436)]3–3[7(350)3+318(410)3+316(460)]3 3 =3911863kJ3mol3 91 (b) (i) O][H ][CO][HK 2 2 c = 3 Unit3of3K c3is3mol3dm 933 3 (ii) Kc3increases3when3temperature3increases3implies3that3forward3reaction3is3 favoured3at3high3temperature.33 Hence3gasification3of3coal3is3an3endothermic3process. (iii) C3(s)3+3H 2O3(g)3 3H 23(g)3+3CO3(g)3 Low3pressure3favours3the3forward3reaction3which3is3accompanied3by3an3 increase3of3gaseous3molecules.3 Hence3low3pressure3increases3the3yeild3of3synthesis3gas3(H 23&3CO)3 (c) The3steam3will3react3with3CO3and3thus3reduces3its3concentration3in3the3 synthesis3gas.3At3the3same3time,3H 23concentration3in3the3synthesis3gas3is3 increased3by3the3reaction. (d) Production3of3CO 23 leads3to3global3warming.3 (e)3 Abundant3supply3of3coal3relative3to3crude3oil3reserves3/3Coal3is3cheaper3 compared3to3volatile3and3unpredictable3crude3oil3prices.3 3

33 Section B 5 (a) Na 2O3is3giant3ionic3with3strong3ionic3bonds3between3Na+3and3O 293ions.3 Dissolves3readily3in3water3to3give3a3stong3alkali3 Na 2O3+3H2O3→32NaOH3 3 SiO 23is3is3giant3molecular3with3strong3covalent3bonds3between3Si3and3O3atoms.3 It3is3insoluble3in3water.3 3 P 4O10 3is3simple3covalent3with3weak3intermolecular3forces3of3attractions.3It3 dissolves3readily3in3water3to3given3a3strong3acid.3 P 4O10 33+336H2O33 →334H 3PO 43 (b) (i) GeO 23high3melting3point3 ⇒3giant3ionic33 SeO 2 low melting point ⇒ simple covalent (ii) GeO 23amphoteric3oxide3 With3NaOH:33 GeO 233+332OH 933+332H2O3→33Ge(OH) 6 2933 With3HCl3:3 GeO 23+34HCl33 →33GeCl 433+332H2O33 3 SeO 23 is3acidic3oxide3 With3NaOH:33 SeO 233+332OH 933 →33SeO 3 2933+33H2O33 With3HCl3:33 No3reaction3 (c) (i) Amt3of3Cl3in30.103g3SOCl 233=3(0.103 ÷3119.1)3x323=30.001683mol3 Amt3of3Cl3in30.103g3SO 2Cl 23=3(0.103 ÷3135.1)3x323=30.001483mol3 3 mole3of3Cl 933formed3=3mole3of33AgCl3=30.2403 ÷3143.53=30.001673mol3 Oxochloride3is3SOCl 233 (ii) Other3than3HCl,33 SOCl 23gives3H 2SO 3333/33SO 2Cl 23gives3H 2SO 43 (d) (from3alcohols)33 3 e.g.3CH 3CH 2OH3 3 (from carboxylic acids) e.g. CH 3COOH (e) elimination3of3HCl;3NaOH3in3alcohol 3 3

43 6 (a) (i) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 5 10 15 20 25 30 time / min conc of H2O2 / mol dm-3 (ii) measure323successive3half3lives3 →3t ½3 constant3(13.53to314.53min)3 →3reaction31 st 3order3w.r.t.3H 2O23 rate3=3k[H 2O2] (iii) draw3tangent3at3t3=303 initial3rate3=30.03553to30.03853mol3dm 933min 913 3 k3=3initial3rate3 ÷3[H 2O2]33=30.04803to30.05103min 91 (iv) 3 Name3any3one3:3MnO 23/3Fe 3+ 3/3Pt3etc3 (b) (i) (ii) value3of3k3increases3 since3rate3increases3without3increase3in3concentration3of3reactant (c) (i) • concentration3increase3causes3molecules3to3be3closer3together3 • Increased3collision3rate (ii) • temperature3increase3causes3kinetic3energy3to3increase3 • more3molecules3will3possess3energy3equal3to3or3exceeding3 activation3energy

53 6 (d) (i) H2O2333333 →33O 23+332 H+33+332e3 MnO 4 -33+338 H+33+335e33 →33 Mn 2+ 33+334H 2O33 5H 2O233+332 MnO 4 - + 6H + → 5O 2 + 2Mn 2+ + 8H2O mole3of3H 2O23used3=350/10003x30.01003=353x310 943mol3 mole3of3 MnO 4 -3needed3=32/53x353x310 9433=323x310 943mol3 volume3of3 MnO 4 -3=3323x310 943/30.023=30.013dm 33=33103 cm 33 (ii) In3this3titration,313mol3H 2O233 ≡313mole3O 233 mole3O 23produced3=3353x310 943mol3 volume3of3O 23at3room3condtions3=353x310 9433x3243dm 333=33123 cm 3 (e) CH3 C O CO2 CH3 7 (a) (i)3 29bromobutane3 (ii)3 CH3CH2CH2CH2Br 33333333 CH3CHCH2Br CH3 33333 CH3CCH3 CH3 Br 3 (b) (i)3 oxidiation33333333333333333 (ii)3 CH3CH2 C CH3 O 3 (iii)3 Yellow3precipitate3formed.3 CHI 3333and333CH 3CH 2COO 9Na +3 3 (c) (i) Boiling3point:333Compound3 E3<3Compound3 F3<3Compound3 A3 333333333333333333333333333 lowest33333333333333333333333333333333333333333333333333333highest3 3 E3is3non9polar3with3weak3van3der3Waals’s3forces3between3molecules.3 F3and3 A3are3polar3with3stronger3dipole9dipole3attraction3b/w3molecules.3 A3has3more3electrons3than3 F. Van3der3Waals’3forces3stronger3in3 A3than3in3 F. 3 3 (ii) CFCs3lead3to3the3depletion3of3the3ozone3layer.3

63 7 (d) (i) 3 33 3 333333333333333333333333333+3CH 3CH 2OH3 3333333333333333333333333333333 3 3 3 3 3 3 +33H 2O3 3 (ii) 3 3 233333333333333333333333333333333333+3Na 2CO 33 3333333333333233 3 3 3 +3CO 233 3 3 3 3 3 +3H 2O3 3 (iii) 3 3 3 33333333333333333333333333+34[H]3 3 +3H 2O33 3 (e) 2,29dichlorobutanoic3acid3has323highly3electronegative3Cl3atoms 3to3exert3electron9 withdrawing 3effect3on3the3–COO 93ion3/3COOH3group.3 3 The3negative3charge3becomes3more3delocalized3and3the3ion3becomes3more3stable.3/3 The3dissociation32,29dichlorobutanoic3acid3is3more3favoured.33 3 Hence32,29dichlorobutanoic3acid3is3a3stronger3 acid. 3 3 (f) (i)3 Add32,49dinitrophenylhydrazine3to3both3compounds.3 3 Compound3S3will3give3a3yellow/orange3precipitate3but3Tamoxifen3will3not.3 (ii)3 3 Percentage3mass3of3C3=3 100%16.014.031(1.0)26(12.0) 26(12.0) ×+++ 3 3 3 3 =3 100%373 312 × 3 3 3 3 333333333333333333=383.63%3 3 3 Paper 1 (MCQ) Answers 1 B 7 D 13 A 19 D 25 C 2 D 8 B 14 B 20 C 26 B 3 C 9 D 15 C 21 B 27 B 4 B 10 C 16 D 22 D 28 D 5 A 11 A 17 C 23 C 29 C 6 A 12 C 18 A 24 A 30 A COOH C O O CH 2CH3 COOH COO9Na+ COOH CH2OH