Which statement best explains why exactly twice as much 0.100 M NaOH is required to…
CHEMISTRY · Single correct · AP · Chemistry · Acids and Bases · Acids and Bases
Problem
Which statement best explains why exactly twice as much 0.100 M NaOH is required to reach the second equivalence point as the first when titrating a diprotic acid H₂A of fixed initial concentration and volume?
(a) Because the second ionization constant of H2A is much smaller than the first, twice as many moles of base are needed to force the second deprotonation to completion.
(b) Only half of the acid molecules actually lose a proton before the first equivalence point, so the remaining half require an equal additional volume of base.
(c) Because each molecule of H2A donates two protons that react with OH− in separate 1:1 steps, another equivalent of base equal to the first is required to remove the second proton.
(d) The volume of the solution has doubled by the time the first equivalence point is reached, diluting the added base so that an extra equal volume must be delivered to reach the second equivalence point.