What is the ratio of pH of a solution containing 1 mole of and 1 mole of per litre and the other sol — Ionic Equilibrium Chemistry Question
Question
What is the ratio of pH of a solution containing 1 mole of $\text{CH}_3\text{COONa}$ and 1 mole of $\text{HCl}$ per litre and the other solution containing 1 mole of $\text{CH}_3\text{COONa}$ and 1 mole of $\text{CH}_3\text{COOH}$ per litre?
💡 Solution & Explanation
In Solution 1, 1 mole of $\text{CH}_3\text{COONa}$ reacts fully with 1 mole of $\text{HCl}$ to form 1 mole of $\text{CH}_3\text{COOH}$ in 1 L. This is a pure weak acid solution with $C = 1 \text{ M}$. $[\text{H}^+] = \sqrt{K_a C} = \sqrt{K_a}$, making $\text{pH}_1 = \frac{1}{2} pK_a$. In Solution 2, 1 mole of $\text{CH}_3\text{COONa}$ and 1 mole of $\text{CH}_3\text{COOH}$ in 1 L form a buffer. Since $[\text{Salt}] = [\text{Acid}]$, $\text{pH}_2 = pK_a + \log(1) = pK_a$. The ratio $\text{pH}_1 : \text{pH}_2 = \frac{1}{2} pK_a : pK_a = 1 : 2$. Therefore, correct answer is A.