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Question
Calculate the pH of buffer solution composed of 0.01 M weak base BOH and 0.02 M of its salt BA. [Kb = 1.8 × 10–5 for weak base]
Solution
pOH = pKb + log10 `(["Salt"])/(["Base"])`
Now, pKb = – log10 Kb
= 5 – log101.8
= 5 – 0.2553
pKb = 4.7447
Then, pOH = 4.7447 + log10 `0.02/0.01`
= 4.7447 + log102
= 4.7447 + 0.3010
pOH = 5.0457
∵ pH + pOH = 14
∴ pH = 14 – pOH
= 14 – 5.0457
= 8.9543 or 8.9
pH = 8.95
The pH of the buffer solution will be 8.95.
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