A chemist titrates 40.0 mL of 0.250 M HBr with 0.300 M NaOH at 25 °C
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A chemist titrates 40.0 mL of 0.250 M HBr with 0.300 M NaOH at 25 °C. The chemist wants to know precisely how much NaOH must be added
(i) to reach a solution pH of 12.00 and
(ii) how sensitive the pH is to further additions once that point is reached.
Assume ideal solution behavior and additive volumes.
(1) Derive an algebraic expression that relates the pH of the solution to the total volume of NaOH added beyond the equivalence point. Express your result in terms of the relevant variables without substituting numbers.
(2) Using your expression from part (a), calculate the additional volume of NaOH (beyond the equivalence point) required to produce a pH of 12.00.
(3) If exactly twice the volume calculated in part (b) were instead delivered, determine the new pH and compute the percentage change in pH relative to 12.00. Explain briefly why the change is larger or smaller than might be expected from a simple doubling of volume.