Question 18.4: Identifying Conjugate Acid-Base Pairs Problem The following ......
Identifying Conjugate Acid-Base Pairs
Problem The following reactions are important environmental processes. Identify the conjugate acid-base pairs.
(a) H_2PO_4^−(aq) + CO_3^{2−}(aq) \xrightleftharpoons[] HCO_3^−(aq) + HPO_4^{2−}(aq)
(b) H_2O(l) + SO_3^{2−}(aq) \xrightleftharpoons[] OH^−(aq) + HSO_3^−(aq)
Plan To find the conjugate pairs, we find the species that donated an H^+ (acid) and the species that accepted it (base). The acid (or base) on the left becomes its conjugate base (or conjugate acid) on the right. Remember, the conjugate acid has one more H and one fewer negative charge than its conjugate base.
Solution (a) H_2PO_4^− has one more H^+ than HPO_4^{2−}; CO_3^{2−} has one fewer H^+ than HCO_3^−. Therefore, H_2PO_4^− and HCO_3^− are the acids, and HPO_4^{2−} and CO_3^{2−} are the bases. The conjugate acid-base pairs are H_2PO_4^−/HPO_4^{2−} and HCO_3^−/CO_3^{2−}.
(b) H_2O has one more H^+ than OH^−; SO_3^{2−} has one fewer H^+ than HSO_3^{−}. The acids are H_2O and HSO_3^−; the bases are OH^− and SO_3^{2−}. The conjugate acid-base pairs are H_2O/OH^− and HSO_3^−/SO_3^{2−}.