Question

Be sure to answer all parts. A buffer consists of 0.38 M KHCO3 and 0.71 M K2CO3. Carbonic acid is a diprotic acid with Ka1 = 4.5 × 10−7 and Ka2 = 4.7 × 10−11. (a) Which Ka value is more important to this buffer?

Answer 1

Explanation:

The dissociation equations for the carbonic acid are as follows.

    $H_{2}CO_{3}(aq) + H_{2}O(l) \rightarrow HCO^{-}_{3}(aq) + H_{3}O^{+}(aq)$

  $HCO^{-}_{3}(aq) + H_{2}O(l) \rightarrow (CO^{2-}_{3})(aq) + H_{3}O^{+}(aq)$

The given buffer contains $KHCO_{3}$ and $K_{2}CO_{3}$. This means that there will be $HCO^{-}_{3}$ ions and $CO^{2-}_{3}$ ions and since, both of them are present in the second step.

Therefore, $K_{a2}$ is more significant with respect to this reaction.

Thus, we can conclude that $K_{a2}$ is more important to this buffer.