AJC_H2 CHEM_P3 ANS

ANDERSON JUNIOR COLLEGE 2009 PRELIMINARY EXAMINATION HIGHER 2 CHEMISTRY PAPER 3 SOLUTIONS AJC 2009 Prelim H2 Chem Paper 3 Solutions 1 1 (a) (i) CH3COCH3 (l) + 4O2 (g)  3CO2 (g) + 3H2O (l) (ii) Heat absorbed by water = 0.70 x 0.050 x 1790 = 62.65 kJ Let m be the maximum mass of water brought to boiling. Heat absorbed by water = mc∆T = m(4.20)(100-15) = 357m J 357m = 62 650 m = 175 g (iii) Heat loss to surroundings. (iv) Since the forward reaction is accompanied by a decrease in number of moles of gaseous particles (n = -1) and there is less disorder (or disorder decreases) which results in a negative entropy change. (v) ΔG = ΔH - TΔS Since ΔS = negative and ΔH = negative, a high temperature will give rise to an increase in  TΔS  such that  TΔS  >  ΔH  , ΔG becomes positive and therefore reaction is not feasible. (b) (i) ΔH at (propanone) CH 3COCH3(l) 3C(g) + 6H(g) + O(g) 3(+715) - 248 6(+218) +249 3C(s) + 3H 2(g) + ½ O2(g) By Hess’ Law, ΔH  at (propanone) = + 3950 kJ mol-1 (ii) ΔHat (propanone) = 2BE(C-C) + 6BE(C-H) + BE(C=O) = 2(+350) + 6(+410) + (+740) = + 3900 kJ mol-1 (iii) ΔH vaporisation (propanone) = + 3950 – 3900 = + 50 kJ mol-1

(c) 2 (a) (i) Nucleophilic substitution C NH2 H ClNC H C NH2 H H ClNC NC C NH2 H H + Cltransition state C---C bond partially formed C---Cl bond partially broken (ii) Reaction II : LiAlH4 in dry ether (or anhydrous) OR H2(g) over Pt catalyst Reaction III : (limiting) Cl2, presence of uv light (or heat) Reaction IV : KOH in ethanol (or alcoholic KOH), reflux CH3COCH3, CH3CH2COONH4, C4H9CHO, CH CH =CHCH (OH) To each sample, add Br2(aq) in the dark AJC 2009 Prelim H2 Chem Paper 3 Solutions 2 CH3CH2=CHCH2(OH) White fu CH3COCH3,CH3CH2COONH4, C H CHO No white fumes observed CH3CH2COONH4 CH3COCH3, C4H9CHO, To each sample, add aqueous NaOH and warm No gas evolved To each sample, add Tollen’s reagent and warm C4H9CHO Silver mirror CH3CH2COCH2CH3 No silver mirror add 2,4-dinitrophenylhydrazine Orange ppt Pungent gas evolved. Turns moist red litmus blue. Orange solution decolorizes Solution remains orange

(iii) H2NC HC H 2NH2 Cl (b) E Heat with NaOH (aq) and acidify with excess dilute HNO3. Add AgNO3 (aq). chloromethylamine : white ppt and E : cream ppt F Add Br2 (aq