Q4. This question is about acidic solutions. (a) The acid dissociation constant, Ka, for ethanoic acid is given by the expression [CH₂COO-][H+] [CH₂COOH] Ka -3 The value of K₂ for ethanoic

acid is 1.74 x 10-5 mol dm-³ at 25 °C A buffer solution with a pH of 3.87 was prepared using ethanoic acid and sodium ethanoate. In the buffer solution, the concentration of ethanoate ions was 0.136 mol dm¯³ Calculate the concentration of the ethanoic acid in the buffer solution. Give your answer to three significant figures. Concentration of acid - mol dm 3 (b) In a different buffer solution, the concentration of ethanoic acid was 0.260 mol dm-³ and the concentration of ethanoate ions was 0.121 mol dm¯ -3 A 7.00 × 10-3 mol sample of sodium hydroxide was added to 500 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. (3)/n(C) A buffer solution with a pH of 4.5 is made by dissolving x g of sodium propanoate (C₂H5 COONa) in a solution of propanoic acid. The final volume of the buffer solution is 500 cm³, and the final concentration of the propanoic acid is 0.50 mol dm-3 .The value of K₂= 1.74 × 10-5 mol dm-3 at 25 °C