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 Sect