This question is about acidic solutions.
The acid dissociation constant, KaK_{\text{a}}Ka, for propanoic acid is given by the expression
Ka=[C2H5COO−][H+][C2H5COOH] K_{\text{a}} = \frac{[\text{C}_2\text{H}_5\text{COO}^-][\text{H}^+]}{[\text{C}_2\text{H}_5\text{COOH}]} Ka=[C2H5COOH][C2H5COO−][H+]The value of KaK_{\text{a}}Ka, for propanoic acid is 1.35×10−5 mol dm−31.35 \times 10^{-5} \text{ mol dm}^{-3}1.35×10−5 mol dm−3 at 25 ∘C25\ ^\circ\text{C}25 ∘C.
A buffer solution with a pH of 4.754.754.75 was prepared using propanoic acid and sodium propanoate. In the buffer solution, the concentration of propanoate ions was 0.185 mol dm−30.185 \text{ mol dm}^{-3}0.185 mol dm−3.
Calculate the concentration of the propanoic acid in the buffer solution. Give your answer to three significant figures.
In a different buffer solution, the concentration of propanoic acid was 0.350 mol dm−30.350 \text{ mol dm}^{-3}0.350 mol dm−3 and the concentration of propanoate ions was 0.220 mol dm−30.220 \text{ mol dm}^{-3}0.220 mol dm−3.
A 1.50×10−2 mol1.50 \times 10^{-2} \text{ mol}1.50×10−2 mol sample of sodium hydroxide was added to 750 cm3750 \text{ cm}^3750 cm3 of this buffer solution.
Calculate the pH of the buffer solution after the sodium hydroxide was added. Give your answer to two decimal places.
