NJC H2 Chem 2012 Prelim P3 Soln

NJC SH2 Preliminary Examinations Paper 3 Solutions 1(a) Pressure is approximately zero at A Volume occupied by gas particles is small compared to the volume of the container \NH3 is almost an ideal gas. Low pressure at B, intermolecular attractions are dominant, thus NH3 molecules are pulled closer together. This reduces the impact on wall collisions and makes them softer. P NH3 < P ideal , hence the negative deviation. Volume occupied by gas particles is still relatively small compared to container. High pressure at D , mainly repulsion between particles. The volume of the molecules becomes a significant fraction of the volume of the container, and thus is no longer negligible. VNH3> Videal, hence the positive deviation. At C, NH3 appears to follow the ideal gas equation, because the two deviations balance out. 1(b)(i) A relatively low temperature of 400 o C is used to increase the yield of the exothermic reaction. Iron catalyst is used to compensate for any reduction in rate due to the low temperature used. A high pressure of 200 atm caters to the forward reaction, which is accompanied by a reduction in volume. Pressure exceeding 200 atm would increase the cost of production. 1(b)(iii) PNH3 = 0.363 x 200 = 72.6 atm PH2 = 0.47775 x 200 = 95.55 atm PN2 = 0.15925 x 200 = 31.85 atm Kp = = 1.90 x 10-4 atm-2 1(c) The - NH2 in hydrazine has a stronger electron-withdrawing effect than the – H in ammonia \the lone pair of electrons in ammonia is more available for donation to a proton \ the stronger base & the bigger Kb value 1(d)(i) Hydrazine and water form a miscible mixture Free intermingling of the molecules of hydrazine & water through mutual H- bonding \ Exists as a homogeneous phase 1

2 dd dd N N H H H H dd dd N N H H H H d d d d NN H H H H d d d d N N H H H H H O H d+ d+ H O H d+ d+ H O H d+ d+ H O Hd+ d+ H-bond Hydrazine and trichloromethane are immiscible Segregation between the molecules of hydrazine & trichloromethane into 2 distinct layers • NH2NH2 have strong H-bond with one another • CHCl3 have van der Waals attraction for one another Each cannot establish any significant attraction for the other and will be squeezed out from one another’s layer N N H H H H N N H H H H N N H H H H N N H H H HN N H H H H _________________________________________Phase boundary C H Cl Cl Cl d+ d- Van der Waals forces H-bond

3 1(d)(ii) -2 oxidation state in N of hydrazine is oxidized to 0 in N2 1(e)(i) C CH 3H2NN CHI3 CH(OH)CH3 Compound E Compound F Compound G 1(e)(ii) Reagent X is I2(aq) with NaOH(aq); and the reaction mixture is warmed. 1(f) CH2CHO Compound H 2 a (i) Distillation and collect the distillate that boils over at 150 OC. (ii) Solid BaSO4 will be formed and it can be removed by filtration. (iii) b (i) Ba + 2H2O ® Ba(OH)2 + H2 (ii) Reaction in b(i) involves the reduction of water by the group II metals. Reaction is more vigo