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Calculate the pOH of 10-8 M of HCl.

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Question

Calculate the pOH of 10-8 M of HCl.

Numerical
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Solution

10-8 M indicates a very dilute solution. Thus, H+ ions of water cannot be ignored. But dissociation of water is suppressed due to common ion effect.

∴ [H+] ≠ 10-7 M but less than 10-7 M.

\[\ce{H2O ⇌ \underset{\ce{(10^{-8} + α)}}{H^+ } + \underset{\text{α}}{OH-}}\]

Kw = [H+] [OH] = (10–8 + α) α

∴ α2 + α × 10-8 - 10-14 = 0

Solving above quadratic equation, we get

α = 0.95 × 10–7

∴ [H+] = 10-8 + 0.95 × 10-7 = 1.05 × 10-7 M

∴ pH = – log10[H+]

= - log10[1.05 × 10-7]

= 6.9788

∴ pOH = 14 – 6.9788 = 7.0212 ≈ 7

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Chapter 3: Ionic Equilibria - Very short answer questions

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SCERT Maharashtra Chemistry [English] Standard 12 Maharashtra State Board
Chapter 3 Ionic Equilibria
Very short answer questions | Q 8

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