Question

what combination of acid and base does this titration curve represent?

a weak base titrated with a weak acid.
a strong base titrated with a strong acid.
a weak base titrated with a strong acid.
a strong base titrated with a weak acid.

Explanation:

Analyze the initial pH of the analyte

Using the pH Calculation knowledge point

$$ \text{Initial pH} \approx 11 $$

Since the initial pH is around 11 (greater than 7 but less than 13-14), the analyte in the flask is a weak base.

Determine the titrant added

Using the Weak Acid Ionization knowledge point

$$ \text{Final pH} \approx 1 $$

As volume increases, the pH drops to approximately 1. This very low final pH indicates that the titrant being added from the burette is a strong acid.

Identify the equivalence point pH

Using the Weak Acid Ionization knowledge point

$$ \text{Equivalence Point pH} \approx 5.5 $$

The steepest vertical region of the titration curve is centered around a pH of approximately 5.5. An equivalence point below 7 is characteristic of a weak base titrated with a strong acid.

Match with the correct option

Using the Weak Acid Ionization knowledge point

$$ \text{Combination} = \text{Weak base titrated with a strong acid} $$

This matches the third option.

Answer:

• A weak base titrated with a weak acid.
• A strong base titrated with a strong acid.
• A weak base titrated with a strong acid. (Correct answer)
• A strong base titrated with a weak acid.