(b) (i) The added OH– reacts with HA or H+ (1) The equilibrium, HA H+ + A– , displacement to right or HA ionises (1) (ii) The added H+ reacts with A– (1) The equilibrium, HA H+ + A–, displaced to left 4 (1) [13] 6. (a) CO + H+  HCO or Na2CO3 + HCl  NaHCO3 + NaCl (1) HCO + H+ H2O + CO2 or NaHCO3 + HCl NaCl + CO2 + H2O (1) or H2CO3   2 (b) 15 cm3 1 (c) Methyl orange (allow other correct indicators) (1) Indicator Methyl red changes colour over pH Explanation range 3.2 4.4 (allow between 3 and 7) (1) 2 – (d) CO + 2H+  H2O + CO2 Mol H+ = 30 × 0.12/1000 = 3.6 × 10–3 (1) Mol CO = 1.8 × 10–3 = M × 25/1000 (1) = 0.072 M (1) 3 (e) 15 (1) Volume of HCl(aq) added for first end-point 45 (1) 2 Volume of HCl(aq) added for second end-point [10] (a) A proton donor 1 7. (b) HCl(g) + H2O(l) H3O+(aq) + Cl–(aq) (1) Equation base or proton acceptor (1) 2 Role of water (c) NH3(g) + H2O(l) NH(aq) + OH–(aq) (1) Equation acid or proton donor (1) 2 Role of water (d) H2SO4 + HNO3 HSO + H2NO (1) Equation for formation base or proton acceptor (1) Role of nitric acid
(b) (i) The added OH– reacts with HA or H+ (1) The equilibrium, HA H+ + A– , displacement to right or HA ionises (1) (ii) The added H+ reacts with A– (1) The equilibrium, HA H+ + A–, displaced to left (1) 4 [13] 6. (a) CO + H+  HCO or Na2CO3 + HCl  NaHCO3 + NaCl (1) HCO + H+  H2O + CO2 or NaHCO3 + HCl  NaCl + CO2 + H2O (1) or H2CO3 2 (b) 15 cm3 1 (c) Indicator Methyl orange (allow other correct indicators) (1) Explanation Methyl red changes colour over pH range 3.2 – 4.4 (allow between 3 and 7) (1) 2 (d) CO + 2H+  H2O + CO2 Mol H+ = 30 × 0.12/1000 = 3.6 × 10–3 (1) Mol CO = 1.8 × 10–3 = M × 25/1000 (1) = 0.072 M (1) 3 (e) Volume of HCl(aq) added for first end-point 15 (1) Volume of HCl(aq) added for second end-point 45 (1) 2 [10] 7. (a) A proton donor 1 (b) Equation HCl(g) + H2O(l) H3O+(aq) + Cl–(aq) (1) Role of water base or proton acceptor (1) 2 (c) Equation NH3(g) + H2O(l) NH(aq) + OH–(aq) (1) Role of water acid or proton donor (1) 2 (d) Equation for formation H2SO4 + HNO3 HSO + H2NO (1) Role of nitric acid base or proton acceptor (1)