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Question:

pKa of a weak acid (HA) and pKb of a weak base (BOH) are 3.2 and 3.4, respectively. The pH of their salt (AB) solution is:

7.2

1.0

6.9

7.0

Solution:

We know, pH = 1/2(pKw + pKa - pKb)
Given pKa = 3.2 and pKb = 3.4
At 298 K, pKw = 14
Therefore, pH = 1/2(14 + 3.2 - 3.4) = 1/2(13.8) = 6.9