An amphoteric salt is one that contains an anion that can act as either an acid

Question

An amphoteric salt is one that contains an anion that can act as either an acid or a base in water Baking soda, NaHCO_3, is an example. By combining the ionization and hydrolysis reactions of the anion, we get the principle reaction that occurs when this salt is dissolved in water. 2HCO_3^-(aq) CO_3^2-(aq) + H_2 CO_3(aq) The pH for such a solution is given by pH = p^K_a1 + pK_a2/2 where K_a1 and K_a2 are the ionization constants of the acid (in this case. H_2CO_3). Note that the pH of the solution is independent of the salt concentration. Calculate the pH of a NaHCO_3 solution. pH =

Explanation / Answer

pH = pKa1 + pKa2 / 2

Ka1 = 4.3 * 10-7 ; Ka2 = 4.8 * 10-11

pKa1 = - log Ka1 = 6.37

pKa2 = - log Ka2 = 10.32

pH = pKa1 + pKa2 / 2 = 6.37 + 10.32 / 2 = 8.345

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