Chemistry?

Suppose 30.00 mL of 0.100 M HCl is added to an acetate buffer prepared by dissolving 0.100 mol of acetic acid and 0.110 mol of sodium acetate in 0.100 L of solution. What are the initial and final pH values?

CH₃COOH(aq) + H₂O(l) ⇌ CH₃COO⁻(aq) + H₃O⁺(aq)

Before addition of HCl :
pH = pKa - log([CH₃COOH]/[CH₃COO⁻]) = -log(1.8 × 10⁻⁵) - log(0.100/0.110) = 4.79

After addition of HCl :
The final volume = (30 + 100) mL = 130 mL
CH₃COO⁻(aq) + H₃O⁺(aq) → CH₃COOH(aq) + H₂O(l)
[CH₃COOH] = 0.100 × (100/130) + 0.100 × (30/130) = 0.100 M
[CH₃COO⁻] = 0.110 × (100/130) - 0.100 × (30/130) = 0.0615 M
pH = pKa - log([CH₃COOH]/[CH₃COO⁻]) = -log(1.8 × 10⁻⁵) - log(0.100/0.0615) = 4.53


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What would be the pH if the same amount of HCl solution were added to 145 mL of pure water?

Total volume = (30 + 145) = 175 mL
[HCl] = 0.100 × (30/175) = 0.0171 M
[H⁺] = 0.0171 M
pH = -log(0.0171) = 1.77