An aqueous solution is obtained by mixing of with of . What would be the precise pH of the resulting — Ionic Equilibrium Chemistry Question
Question
An aqueous solution is obtained by mixing $100 \text{ mL}$ of $0.2 \text{ M } CH_3COOH$ with $100 \text{ mL}$ of $0.2 \text{ M } NaOH$. What would be the precise pH of the resulting solution at $25^\circ C$? (Given $pK_a$ for $CH_3COOH = 4.74$ and $\log 2 = 0.30$).
Answer: B
💡 Solution & Explanation
Mixing equal volumes of $0.2 \text{ M }$ weak acid and $0.2 \text{ M }$ strong base results in complete neutralization, forming a $0.1 \text{ M }$ solution of sodium acetate ($CH_3COONa$) with a total volume of $200 \text{ mL}$. This salt undergoes anionic hydrolysis. The pH is given by $pH = 7 + \frac{1}{2}(pK_a + \log C)$. Here, $C = 0.1 \text{ M}$. $pH = 7 + \frac{1}{2}(4.74 + \log 0.1) = 7 + \frac{1}{2}(4.74 - 1) = 7 + \frac{1}{2}(3.74) = 7 + 1.87 = 8.87$.
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