RI 2022 A-Level H2 Chem Solution

This document is copyrighted, please do not reproduce it without permission © Raffles Institution 2022 A-Level H2 Chemistry Paper 1 Suggested Solutions 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 C C D C A B A B B D D C B B C 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 C A C B C A B B B D D A A D D Q1(C ) The ionic bonds in NaF requires the most energy to overcome while the instantaneous dipole- induced dipole in CH3CH2CH2CH3 requires the least energy to overcome, thus NaF has the highest boiling point while CH3CH2CH2CH3 has the lowest boiling point. Both CH 3CH2NH2 and CH 3CH2OH can form an average of one intermolecular hydrogen bond per molecule. The more polar O−H bond in CH3CH2OH results in stronger hydrogen bonds between CH3CH2OH molec ules compared to the less polar N−H bond in CH 3CH2NH2, thus CH 3CH2OH has a higher boiling point than CH3CH2NH2. Q2(C ) A Incorrect. Br is less electronegative than Cl. B Incorrect. Having the same outer shell electronic configuration does not explain why the Br−Cl bond is polar. C Correct. Since Br has one additional electronic shell than Cl, its outer shell electrons are more shielded from the nuclear charge and hence the shared pair of electrons in the Br−C l bond is less attracted to Br, making Br less electronegative than C l, resulting in a polar Br−Cl bond. D Incorrect. Since Br and Cl have the same outer shell electronic configuration, the repulsion between electrons in the outer shell will be similar in both atoms. Q3(D ) 1 Incorrect. Ethanoic acid has a higher pKa and hence smaller K a, thus is a weaker acid than thioacetic acid. S o H+ is not more easily removed from ethanoic acid. 2 Incorrect. Ethanoic acid has a higher p Ka and hence smaller Ka than thioacetic acid. 3 Correct. Thioacetic acid has a smaller p Ka and hence higher K a, is a stronger weak acid than ethanoic acid. The weaker S−H bond in thioacetic acid allows for greater extent of ionisation, and at the same concentration, thioacetic acid will form a higher concentration of H +, giving a solution of lower pH than ethanoic acid. Q4(C ) At the same temperature and pressure, since there is same number of moles of O2 and N2O in entonox gas, PO2 = PN2O. Since PT = 3.55 × 107Pa, PN2O = 3.55 × 107 2 = 1.775× 107Pa Assuming N2O behaves as an ideal gas, pV = nRT = M Mr RT Mass of N2O = pVMr RT = 1.775× 107× 5 1000 × ( 14.0 × 2 + 16.0) 8.31 × ( 273+20) = 1604 g ≈ 1.60 kg Q5(A ) 1 Correct. AlCl3 hydrolyses in water to give a solution of pH 3 , which will cause a vigorous effervescence when added to Na2CO3. AlCl3(s) + 6H2O(l) → [Al(H2O)6]3+(aq) + 3Cl–(aq) [Al(H2O)6]3+(aq) ⇌ [Al(H2O)5(OH)]2+(aq) + H+(aq) 2 Incorrect. While Mg Cl2 hydrolyses slightly in water to give a weakly acidic solution of pH 6.5, it will not give a vigorous effervescence when added to Na2CO3 due to the lower concentration of H +, resulting in a slower rate of reaction. MgC