NJC_Prelim_P3 ANS

Prelim 2009 H2 Chemistry P3 solutions (a) Electronegativity is defined as the ability of an atom to attract bonding pair of electrons to itself in a covalent bond. Oxygen atom is more electronegative than Nitrogen atom.  Oxygen has a greater nuclear charge than Nitrogen atom.  They have same screening effect.  Effective nuclear charge of O atom is greater than that of N atom; it will attract the bonding electrons more strongly. (b) (i) Shape of N2O is linear. Bond angle is 180o. (b) (ii) N2O will require the highest temperature to behave like an ideal gas.  Ideal Gas Assumption: Negligible forces of attraction or repulsion between the particles.  N 2O exhibit permanent dipole-dipole interactions while the other 2 are exhibit temp dipole-induced dipole interactions.  Since pd-d is stronger than td-id; a higher temperature is required to overcome the intermolecular bonds between N2O molecules for it to be ideal. (c) (i) By plotting a graph partial pressure against time; it was found that the half life is constant at 3500 s; hence reaction is first order with respect to N2O. t 1/2 = ln 2 k k = 1.98 × 104 s1 (d) (i) Electrophilic substitution (ii) Lone pair on oxygen atom of phenol is delocalized into the benzene ring, making it more reactive (more activated). more able to attract the electrophile, the diazonium ion. (e) (i) OCH2CH3 (ii) OH dilute HNO3 OH NO2 Sn in x.s conc HCl NaOH OH NH2 1

2 (i)(I) Minimum ] [Ag 314 moldm 10 52 . 8  (II) Minimum [Ag+] 35 moldm 10 17 . 3  (ii) 312 moldm 10 2.69 ] [I   (b)(i) The reaction mixture must be titrated quickl y or else the position of equilibrium will shift This will cause the measured amount of thiosulfate used to be inaccurate. (ii) -3 c 10 98 . 3 K  (c) Electrop hilic addition C H2 C CH3 H HI slow C H3 C + CH3 H C H3 C CH2 + H H carbocation intermediate A carbocation intermediate B C H3 C + CH3 H C H3 C CH2 + H H carbocation intermediate A carbocation intermediate B step I step II + I - - I - I CH3 C HC H3 I CH3CH2CH2I δ- δ+ Carbocation A is more stable than carbocation B, and A wo uld lead to the major product. (d) COOH CH HI O H COI CH323    A undergoes complete hydrolysis, resulting in the formation of a strong acid HI, which completely dissociates in H+. - 3322 COO CH O H O H ICOOHCH    B is a weak acid that undergoes partial dissociation, resulting in lesser moles of H+ than in the case of A and therefore A would have pH 0.5 and B pH 3.0. (e) IC H3 C C H3 D C H3 O OH O E C H3 OH OH O F 2

3(a) pH = 2.375 (bi) Heat energy released by the neutralization process to complete the dissociation of CH3COOH. (bii) ΔHneut = -57.3 kJ mol-1 (ci) CH 3COOH – hydrogen bonding CH3COSH & CH3COSeH – td-id Energy required : H-bonding > td-id CH3COSeH – larger electron cloud (cii) ΔHformation(H-bonding) = - 24.5 kJ mol-1 (