Sketch two pH curves, one for the titration of a weak acid with a strong base and one for a strong acid with a strong base. How are they similar? How are they different? Account for the similarities and the differences

In titration, a solution of known concentration (the titrant) is added to a solution of unknown concentration (the analyte) to determine the concentration of the analyte. The point at which the analyte has been completely neutralized by the titrant is known as the equivalence point. In our exercise, we have two scenarios: weak acid titrated with a strong base, and strong acid titrated with a strong base. Weak acids do not ionize completely, meaning only a small percentage of the acid molecules release hydrogen ions (H+) during the reaction. As a result, the pH at the equivalence point of the titration involving a weak acid will be more than 7 due to the presence of the conjugate base produced. On the other hand, strong acids ionize completely, releasing all their hydrogen ions during the reaction. This results in a pH at the equivalence point that is exactly 7.

First, let's sketch the curve for a weak acid with a strong base: 1. At the beginning, the pH is low due to the weak acid, but it is not as low as for a strong acid. 2. As the strong base is added, the pH increases slowly at first and then more rapidly as the equivalence point approaches. 3. At the equivalence point, the pH will be greater than 7 because the weak acid is neutralized by the strong base and a leftover conjugate base is produced, which is alkaline. 4. After the equivalence point, the curve becomes more horizontal as the excess strong base causes the pH to level off at a higher value. Now, let's sketch the curve for a strong acid with a strong base: 1. At the beginning, the pH is very low due to the strong acid. 2. As the strong base is added, the pH increases rapidly towards the equivalence point. 3. At the equivalence point, the pH is exactly 7 as the strong acid is neutralized by the strong base, leaving a neutral solution. 4. After the equivalence point, the curve becomes more horizontal as the excess strong base causes the pH to level off at a higher value.

Let's now analyze the similarities and differences between the two curves. Similarities: 1. Both curves start at a low pH and end at a high pH. 2. Both curves show a rapid pH increase near the equivalence point. 3. Both curves become more horizontal after the equivalence point. Differences: 1. The pH curve for a weak acid with a strong base starts at a higher pH than the curve for a strong acid with a strong base because weak acids are less acidic than strong acids. 2. The weak acid-strong base curve has a more gradual initial increase in pH as compared to the strong acid-strong base curve. 3. The pH at the equivalence point for the weak acid-strong base titration is greater than 7, while it is exactly 7 for the strong acid-strong base titration. 4. The weak acid-strong base curve has a gentle sigmoidal shape whereas the strong acid-strong base curve has a steep sigmoidal shape.

The similarities between the two curves are due to the common process of titration and the addition of a strong base to neutralize the acid. This causes an increase in pH and leveling off after the equivalence point. The differences between the curves can be explained by the different properties of strong and weak acids. Weak acids do not dissociate completely in a solution, so the initial pH is higher and the increase in pH is more gradual. At the equivalence point, the weak acid has been completely neutralized by the strong base, but the leftover conjugate base, being basic, causes the pH to be greater than 7. Meanwhile, a strong acid dissociates completely, resulting in a lower initial pH and a faster increase in pH. At the equivalence point, the strong acid and strong base neutralize each other, leaving a neutral solution with a exactly 7 pH.