A laboratory technician prepares 1.00 L of a buffer solution by mixing 0.25 mol of…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A laboratory technician prepares 1.00 L of a buffer solution by mixing 0.25 mol of acetic acid (CH₃COOH) with 0.25 mol of sodium acetate (CH₃COONa) in water. The initial temperature is 25 °C and the pH of the solution is measured to be 4.74.
Strong acid and strong base are added in separate trials, as described below. In every case, the added volume is small enough that the total volume of the buffer may be considered unchanged.
(1) For Trial 1, predict whether the pH after addition will be greater than, less than, or approximately equal to 4.74. Justify your prediction qualitatively by identifying the species that react and the products formed.
(2) For Trial 2, predict whether the pH after addition will be greater than, less than, or approximately equal to 4.74. Justify your prediction qualitatively by identifying the species that react and the products formed.
(3) Compare the magnitude of the pH change in Trial 1 with that in Trial 3. Explain why any difference exists, citing the relative amounts of conjugate acid–base pairs present.