A buffer is prepared with 0.20 mol of HA (a weak acid) and 0.05 mol of A in 1.0 L of…
CHEMISTRY · Single correct · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A buffer is prepared with 0.20 mol of HA (a weak acid) and 0.05 mol of A− in 1.0 L of solution.
• Student X first adds 0.10 mol NaOH, stirs, then adds 0.10 mol HCl.
• Student Y first adds 0.10 mol HCl, stirs, then adds 0.10 mol NaOH.
Which statement about the pH behavior of the two experiments is most accurate?
(a) Only Student Y’s solution stays within the buffer range throughout the sequence; Student X’s solution experiences a large pH rise after the first addition.
(b) Both solutions remain within the buffer range because the buffer components are present in much larger amounts than the added acid or base.
(c) Only Student X’s solution stays within the buffer range throughout the sequence; Student Y’s solution experiences a large pH drop after the first addition.
(d) Only Student X’s buffer fails; the 0.10 mol of NaOH converts essentially all HA to A−, eliminating the acidic component and causing a large pH increase, while Student Y remains buffered.