Question 6.10: Write a mass balance and charge balance equations for a 0.10...
Write a mass balance and charge balance equations for a 0.10 M solution of NaHCO_3.
It is easier to keep track of what species are in solution if we write down the reactions that control the solution’s composition. These reactions are the dissolution of a soluble salt
NaHCO_3(s) → Na^+(aq) + HCO_3 ^–(aq)
and the acid–base dissociation reactions of HCO_3 ^– and H_2O
HCO_3 ^–(aq) + H_2O(\ell) \rightleftharpoons H_3O+(aq) + CO_3 ^{2–}(aq)
HCO_3 ^–(aq) + H_2O(\ell) \rightleftharpoons OH^–(aq) + H_2CO_3(aq)
2H_2O(\ell) \rightleftharpoons H_3O^+(aq) + OH^–(aq)
The mass balance equations are
0.10 M = [H_2CO_3] + [HCO_3 ^–] + [CO_3 ^{2–}]
0.10 M = [Na^+]
The charge balance equation is
[Na^+] + [H_3O^+] = [OH^–] + [HCO_3 ^–] + 2 × [CO_3 ^{2–}]