Acid/Base Pairs . For each acid–base equilibrium, label the stronger acid, the stronger base, the weaker acid, and the weaker base. Then predict whether the position of equilibrium lies toward the right or toward the left.
(a) H_{2}CO_{3} + OH^{-} \xrightleftharpoons[]{} HCO_{3}^{-} +H_{2} O
(b) HPO_{4} ^{2-} + NH_{3} \xrightleftharpoons[]{} PO_{4} ^{3-}+ NH_{4} ^{+}
Use Table 8.2 to identify the stronger acid from the weaker acid and the stronger base from the weaker base. Once you have done that, determine in which direction the equilibrium lies. It always lies in the direction of the stronger components moving towards the weaker components.
Arrows connect the conjugate acid–base pairs, with the red arrows showing the stronger acid. The position of equilibrium in (a) lies toward the right. In (b) it lies toward the left.
Table 8.2
| Acid | Name | Conjugate Base | Name | ||
 |
\mathrm{HI} | Hydroiodic acid | \mathrm{I}^{-} | Iodide ion |  |
| \mathrm{HCl} | Hydrochloric acid | \mathrm{Cl}^{-} | Chloride ion | ||
| H_{2}SO_{4} | Sulfuric acid | \mathrm{HSO}_{4}^{-} | Hydrogen sulfate ion | ||
| HNO_{3} | Nitric acid | \mathrm{NO}_{3}^{-} | Nitrate ion | ||
| H_{3}O^{+} | Hydronium ion | \mathrm{H}_{2} \mathrm{O} | Water | ||
| HSO_{4}^{-} | Hydrogen sulfate ion | \mathrm{SO}_{4}^{2-} | Sulfate ion | ||
| H_{3}PO_{4} | Phosphoric acid | \mathrm{H}_{2} \mathrm{PO}_{4}^{-} | Dihydrogen phosphate ion | ||
| \mathrm{CH}_{3} \mathrm{COOH} | Acetic acid | \mathrm{CH}_{3} \mathrm{COO}^{-} | Acetate ion | ||
| \mathrm{H}_{2} \mathrm{CO}_{3} | Carbonic acid | \mathrm{HCO}_{3}^{-} | Bicarbonate ion | ||
| \mathrm{H}_{2} \mathrm{~S} | Hydrogen sulfide | \mathrm{HS}^{-} | Hydrogen sulfide ion | ||
| \mathrm{H}_{2} \mathrm{PO}_{4}^{-} | Dihydrogen phosphate ion | \mathrm{HPO}_{4}^{2-} | Hydrogen phosphate ion | ||
| \mathrm{NH}_{4}^{+} | Ammonium ion | \mathrm{NH}_{3} | Ammonia | ||
| \mathrm{HCN} | Hydrocyanic acid | \mathrm{CN}^{-} | Cyanide ion | ||
| \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH} | Phenol | \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}^{-} | Phenoxide ion | ||
| \mathrm{HCO}_{3}^{-} | Bicarbonate ion | \mathrm{CO}_{3}{ }^{2-} | Carbonate ion | ||
| \mathrm{HPO}_{4}^{2-} | Hydrogen phosphate ion | \mathrm{PO}_{4}^{3-} | Phosphate ion | ||
| \mathrm{H}_{2} \mathrm{O} | Water | \mathrm{OH}^{-} | Hydroxide ion | ||
| \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} | Ethanol | \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O}^{-} | Ethoxide ion |