Ph acid/base

Although pH meters are convenient, experimenters may also titrate a weak acid with a strong base and use pH to determine the pKa of the acid. After standardizing the strong base, the experimenter should obtain a measured volume of weak acid and add four drops of phenolphthalein. Because the endpoint in a weak acid-strong base titration is between 8 and 9, the phenolphthalein will appropriately display the neutralization. The initial volume of base in the buret should be recorded before titration. Proceeding with caution, a change from clear to very pale pink will indicate when endpoint is reached. Again, the volume of base in the buret should be recorded.

We know that at the half neutralization point pH=pKa; therefore, the volume used in the above procedure divided by 2 will give the volume of base needed to reach the half neutralization point. Another titration using only the newly calculated amount of base should be performed using the same standardized base and same vol...