Final answer:
Substances that exceed the buffer capacity are those that add more H+ or OH- than the buffer components can neutralize. For this buffer with 2 moles of acetic acid and 3 moles of sodium acetate, adding more than 2 moles of H+ or 3 moles of OH- would exceed its capacity.
Step-by-step explanation:
The question asks which substance will exceed the buffer capacity when added to a buffer composed of 2 moles of acetic acid and 3 moles of sodium acetate in 1 liter of water. Buffer capacity is the ability of a buffer solution to resist changes in pH upon the addition of an acid or base. It depends on the amounts of the weak acid and its conjugate base present in the solution.
A buffer with equal concentrations of a weak acid and its conjugate base is most effective. Once the amount of added H+ or OH- exceeds the number of moles of buffer components, the buffer's capacity is overwhelmed, resulting in a significant pH change.
Therefore, the addition of an acid or base exceeding the amounts of either acetic acid (the weak acid) or sodium acetate (the conjugate base) will exceed the buffer capacity. Since the buffer contains 2 moles of acetic acid and 3 moles of sodium acetate, adding more than 2 moles of H+ or 3 moles of OH- would overwhelm the buffer system and cause a substantial change in pH.