Q.16 Define conjugate acid-base pair. The hydroxyl ion concentration in aqueous solution of NaOH is 2 × 10−4 mol dm−3. Calculate pH of the solution.
Best answer
Answer: pH = 10.30
Conjugate acid-base pair: An acid and a base that differ from each other only by one proton (H+) form a conjugate acid-base pair. E.g. in HCl + H2O ⇌ H3O+ + Cl−, HCl/Cl− and H3O+/H2O are conjugate pairs.
Calculation: \([\mathrm{OH^-}] = 2\times10^{-4}\) M
\(\mathrm{pOH} = -\log(2\times10^{-4}) = 4 - \log 2 = 4 - 0.3010 = 3.699\)
\(\mathrm{pH} = 14 - \mathrm{pOH} = 14 - 3.699 = 10.301\)
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