Carbonic Acid Equilibria

Carbonic acid equilibria Carbonic acid equilibria Three connected reactions … CO2(g) + H2O(l)  (HO)2CO (aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) … that establish simultaneous balance. Effect of acidity on CO2(g) solubility CO2(g) + H2O(l)  (HO)2CO (aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) Adding acid, lowers solubility of CO2(g) in water. Adding base, increases solubility of CO2(g) in water. Response of system illustrates Le Chatelier’s principle Adding NaOH Adding NaOH … disturbs balance by consuming H3O+ CO2(g) + H2O(l)  (HO)2CO (aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) Adding NaOH … which shifts balance toward more products … which consumes (HO)CO22‐ CO2(g) + H2O(l)  (HO)2CO (aq) CO2(g) + H2O(l)  (HO)2CO (aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) Adding NaOH Adding NaOH … which shifts balance toward more products … which consumes (HO)2CO CO2(g) + H2O(l)  (HO)2CO (aq) CO2(g) + H2O(l)  (HO)2CO (aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) Adding NaOH Adding NaOH … which shifts balance toward more products … which consumes CO2 CO2(g) + H2O(l)  (HO)2CO (aq) CO2(g) + H2O(l)  (HO)2CO (aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) … and so balance is restored. Adding HCl Adding HCl … disturbs balance by increasing H3O+ … which shifts balance toward more reactants CO2(g) + H2O(l)  (HO)2CO (aq) CO2(g) + H2O(l)  (HO)2CO (aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) Adding HCl Adding HCl … which forms more (HO)CO2‐ … which shifts balance toward more reactants CO2(g) + H2O(l)  (HO)2CO (aq) CO2(g) + H2O(l)  (HO)2CO (aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) Adding HCl Adding HCl … which forms more (HO)2CO … which shifts balance toward more reactants CO2(g) + H2O(l)  (HO)2CO (aq) CO2(g) + H2O(l)  (HO)2CO (aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO22‐(aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO22‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) Adding HCl … which forms more CO2 Effect of acidity on CO2(g) solubility CO2(g) + H2O(l)  (HO)2CO (aq) CO2(g) + H2O(l)  (HO)2CO (aq) (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) … and so balance is restored (HO)2CO(aq) + H2O(l)  H3O+(aq) + (HO)CO2‐(aq) (HO)CO2‐(aq) + H2O(l)  H3O+(aq) + CO32‐(aq) Adding acid, lowers solubility of CO2(g) in water. Adding base, increases solubility of CO2(g) in water. Response of system illustrates Le Chatelier’s principle