What is the exact pH of a solution of at ? (Given for and ). — Ionic Equilibrium Chemistry Question
Question
What is the exact pH of a $0.1 \text{ M }$ solution of $NH_4Cl$ at $25^\circ C$? (Given $pK_b$ for $NH_4OH = 4.74$ and $\log 0.1 = -1.0$).
Answer: 5.13
💡 Solution & Explanation
$NH_4Cl$ is a salt of a strong acid ($HCl$) and a weak base ($NH_4OH$). The pH of its solution is calculated via the formula: $pH = 7 - \frac{1}{2}pK_b - \frac{1}{2}\log C$. Substituting the given values: $pH = 7 - \frac{1}{2}(4.74) - \frac{1}{2}(-1.0) = 7 - 2.37 + 0.5 = 5.13$.
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