# Question #7259d

Jun 21, 2017
• There is a buffer region in the strong base / weak acid titration curve where the $\text{pH}$ rises slowly, but not the strong base / strong acid titration.
• For the strong base / weak acid titration curve, we do have a half-equivalence point where $\text{pH}$ $\approx$ $\text{pKa}$, but that relationship does not hold true for the strong base / strong acid titration curve.
• $\text{pH}$ at the equivalence point is greater than $7$ for the strong base / weak acid titration and equal to $7$ for the strong base / strong acid titration.

The main qualities (without identified differences yet) you should expect from each kind of titration curve are:

Both curves

• Starting $\text{pH}$ of what is being titrated (what the titrant from the burette is being dripped into) is less than $7$ (after the equivalence point).
• End $\text{pH}$ of what is being titrated is greater than $7$ (after the equivalence point).

Strong base into strong acid

• There is no buffer region on the way to the equivalence point, because we need a weak acid / conjugate base or weak base / conjugate acid combination to have this. This lack of a buffer region is seen as a simple flat rise.
• There is a half-equivalence point, but the $\text{pH}$ is simply given by the concentration of ${\text{H}}^{+}$ in the solution, and bears no relationship to the $\text{pKa}$ of the acid.
• $\text{pH}$ at the equivalence point is exactly $7$ (exact neutralization of all ${\text{H}}^{+}$ and ${\text{OH}}^{-}$ that are not from water).

Strong base into weak acid

• There is a buffer region on the way to the equivalence point where the $\text{pH}$ increases slowly. This is seen as an initial "hill" into a flat rise.
• There is a half-equivalence point, i.e. half the volume of the equivalence point, which has $\text{pH}$ $\approx$ $\text{pKa}$ (from the Henderson-Hasselbalch equation), where $\text{pKa} = - \log {K}_{a}$ and ${K}_{a}$ is the acid dissociation constant.
• $\text{pH}$ at the equivalence point is greater than $7$. You can think of it as the strong base "dominating" the resultant $\text{pH}$ at that point.

DIFFERENCES

In the end, we can summarize the following differences:

• There is a buffer region in the strong base / weak acid titration curve where the $\text{pH}$ rises slowly, but not the strong base / strong acid titration.
• For the strong base / weak acid titration curve, we do have a half-equivalence point where $\text{pH}$ $\approx$ $\text{pKa}$, but that relationship does not hold true for the strong base / strong acid titration curve.
• $\text{pH}$ at the equivalence point is greater than $7$ for the strong base / weak acid titration and equal to $7$ for the strong base / strong acid titration.