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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]

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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]

Short/Brief Note
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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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2021-2022 (March) Set 1

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