NJC H2 Chem 2013 Prelim P3 Soln

NJC SH2 Prelim 2013 H2 Chemistry Paper 3 Solution 1 1a) (i) or Shape about N: Bent (ii) Type of isomerism: cis-trans or geometric isomerism More stable isomer 1b) (i) Dynamic equilibrium refers to an equilibrium reaction when the rate of forward is equal to the rate of backward reaction. Kp = ) P)(P ( P 22 2 2 F N F N Units: Pa-1 or atm-1 (ii) pV = nRT pV = RTM m M = 65 10x500x10x12. 1 500x31. 8 x578. 0 pV mRT  =42.9 gmol-1 N2 F2 N2F2 Initial n/mol 2 1 0 Change of n/mol -x -x x Equilibrium n/mol 2-x 1-x x Total number of moles = (2-x) + (1-x) + x = 3-x 144

NJC SH2 Prelim 2013 H2 Chemistry Paper 3 Solution 2 (Note: sum of mole fraction x Mr for each gases = average Mr) 9 .42)66(x 3 x)38(x 3 x 1)28(x 3 x 2    x = 0.576mol Mole fraction of N 2F2 = gases of moles total F N of moles2 2 = 237. 0576. 0 3 576. 0 x 3 x  (ii) Partial pressure of N 2F2 = mole fraction of N2F2 x total pressure = 0.237 x 1.12 x 105 = 26500 Pa (iii) ∆S is negative. There is a decrease in number of moles of gas in the reaction and the system becomes more ordered. (iii) ∆G=∆H–T∆S. Since ∆S is negative and T is always positive, therefor e, –T∆S is positive. In order for ∆G to be negative, ∆H must be negative and have a magnitude greater than T∆S. 1 c) A = P 2O4 P O 49% 51% Ar mass% 57. 11 .31 49  18. 30 .16 51  Simplest ratio 1 2 Empirical formula of A = PO2 [1] P2O4 + 3H2O → H3PO3 + H3PO4 A 145

NJC SH2 Prelim 2013 H2 Chemistry Paper 3 Solution 3 1 d) (i) C H C H Cl H In chloroethene, as Cl is adjacent to the C=C bond, p-orbital of Cl can overlap with the π electron cloud of C=C bond . Hence lone pair of electrons on Cl is delocalised into the π electron cloud of C=C bond , strengthening C –Cl bond (partial double bond character). Thus C–Cl bond in chloroethene cannot be cleaved, no free Cl– ions formed, hence AgCl ppt is not produced. 1 d) (ii) Greater reactivity of the acyl chloride C –Cl bond in C6H5COCl/ the acyl chloride is more reactive because  the acyl carbon atom is bonded to 2 electronegative atoms, Cl and O which makes the carbon atom more electron-deficient/more partial positive. OR  the electron withdrawing C=O bond makes the carbon atom bonded to Cl more electron-deficient/more partial positive. Hence the δ+ C is more susceptible to nucleophilic attack by water molecules. C–Cl bond breaks readily to give Cl– ions which gives AgCl, white ppt with AgNO3(aq). 2 a) Reducing agent: H2O Relevant data required: Reduction: MnO4  + 4H+ + 3e  MnO2 + 2H2O Eo red = +1.67V Oxidation: 2H2O  O2 + 4H+ + 4e Eo oxid = 1.23V Overall 4MnO4  + 4H+ + 4OH  4MnO2 +2H2O + 3O2 + 4OH Eo cell = +0.44V i.e. 4MnO