When looking at a titration curve, I have to determine which is false and I have it narrowed down to two options:
The initial starting point on the titration curve is where pH depends only on [HA]0
or
The finial point on a titration curve the pH depends only on [A-]
I would think the first option would be false? Considering the finial point would be where only the excess base is left over, but I'm not sure.
To determine which statement is false, let's first understand the concept of a titration curve. A titration curve shows the change in pH of a solution as a reagent (usually an acid or a base) is incrementally added to it.
At the beginning of a titration, the solution contains only the initial acid (HA) that is to be titrated. As the acid reacts with the base being added, its concentration decreases, and the concentration of its conjugate base (A-) increases. This process continues until all the acid is neutralized by the base, leading to the equivalence point.
Now, let's examine the statements you provided:
1. "The initial starting point on the titration curve is where pH depends only on [HA]0."
This statement is true. Initially, as the titration begins, there is no base present to react with the acid. Therefore, the pH of the solution is determined solely by the concentration of the initial acid ([HA]0). The pH at this point can be calculated using the Henderson-Hasselbalch equation (pH = pKa + log([A-]/[HA])).
2. "The final point on a titration curve, the pH depends only on [A-]."
This statement is false. At the final point of the titration, when all the acid has reacted with the base, only the excess base (conjugate base, [A-]) remains. The pH at this point depends on the concentration of the excess base as well as the volume of the base added. The pH can be calculated using a similar Henderson-Hasselbalch equation or by determining the concentration of hydroxide ions (OH-) in the solution.
Therefore, in your narrowed-down options, the false statement is the second one: "The final point on a titration curve, the pH depends only on [A-]."