RVHS_H2_CHEM_P3_ANS Prelim

1 River Valley High School 9647/03/PRELIM/11 Preliminary Examination 2011 RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION H2 CHEMISTRY 9647/03 Paper 3 Free Response Suggested Answers 1ai ∆Hr = BE(bonds broken) – BE(bonds form) = [12BE(N-H) + 3BE(O=O)] – [2(NΞN) + 12(O-H)] = [12(+390) + 3(+496)]  [2(+994)+12(+460)] = 1340 kJ mol-1 1aii The calculated value differs from the theoretical value because the bond energies given in the Data Booklet are only average energies. 1aiii ∆S is expected to be positive as the reaction proceeds with an increase in disorder due to increase in the number of gaseous molecules. ∆G = ∆HT∆S, since ∆S is positive and ∆H is negative, ∆G will always be a negative value. Hence we can conclude that the given reaction is spontaneous. 1aiv Increasing deviation: N2 < O2 < NH3 < H2O Deviation from ideal behaviour depends on the strength of intermolecular forces and number of electrons in the molecule. Weak instantaneous dipole-induced dipole/van der Waals’ forces exist between nitrogen molecules and between oxygen molecules. Strong hydrogen bonds exist between ammonia molecules and water molecules. Water shows more extensive hydrogen bonding than ammonia while oxygen has a larger electron cloud, and therefore stronger instantaneous dipole-induced dipole/van der Waals’ forces than nitrogen. 1bi Haemoglobin consists of four protein chain subunits: two -chain subunits and two - chain subunits, held by non-covalent interactions between R groups: ionic interactions, van der Waals’ forces and hydrogen bonds. 1bii Assuming oxygen is an ideal gas, pV = nRT (98.7 x 10 3)(3.06 x 10-6) = n(8.314)(37+273) n = 1.172 x 10-4 mol

2 River Valley High School 9647/03/PRELIM/11 Preliminary Examination 2011 Amount of haemoglobin = n/4 = 2.930 x 10-5 mol Molar mass of haemoglobin = 2.00/2.930 x 10-5 = 6.83 x 104 g mol-1 1biii Oxygen is not an ideal gas. Intermolecular forces of attraction are present between oxygen molecules. 1ci Valine exhibits optical isomerism. 1cii Van der Waals’ forces between ile, leu, met, phe, val (any two). Hydrogen bonds between lys, thr, trp (any two). C H O C H H H H C H H C H H C H H C H H N H H + + + - - hydrogen bond CH(CH3)(CH2CH3) CH(CH3)2 C H HOOC NH2 CH(CH3)2 C H H2N CH(CH3)2 COOH van der Waals’ forces

3 River Valley High School 9647/03/PRELIM/11 Preliminary Examination 2011 1ciii

4 River Valley High School 9647/03/PRELIM/11 Preliminary Examination 2011 2a A is not soluble in acid : A is not basic. [] Acid hydrolysis [] of A took place to give B and C. A is likely to be an ester [] while B is likely to be an alcohol. [] B rotates plane-polarized light. B has at least 1 chiral C. [] B is oxidized [] by hot acidified KMnO 4 to give D, with the removal of 2 H in D. D is a ketone [] while B is a secondary alcohol. [] D gives a