The equivalence point was reached in titrations of three unknown acids at pH 9.16 (acid A), 8.88 (acid B), and 8.19 (acid C). (a) Which is the strongest acid? (b) Which is the weakest acid?

Verified step by step guidance

1. insert step 1> Determine the relationship between the pH at the equivalence point and the strength of the acid.
2. insert step 2> Recall that the equivalence point pH in a titration of a weak acid with a strong base is greater than 7 and is influenced by the strength of the conjugate base formed.
3. insert step 3> Understand that a lower pH at the equivalence point indicates a stronger acid, as the conjugate base is weaker and less able to raise the pH.
4. insert step 4> Compare the given pH values at the equivalence points: 9.16 (acid A), 8.88 (acid B), and 8.19 (acid C).
5. insert step 5> Identify the strongest acid as the one with the lowest pH at the equivalence point and the weakest acid as the one with the highest pH at the equivalence point.

Key Concepts

Equivalence Point in Titration

The equivalence point in a titration is the stage at which the amount of titrant added is stoichiometrically equivalent to the amount of substance in the sample. At this point, the reaction between the acid and base is complete, and the pH of the solution reflects the properties of the resulting salt and water. The pH at the equivalence point can provide insights into the strength of the acids involved.

Strength of Acids

The strength of an acid is determined by its ability to donate protons (H+) in solution. Strong acids completely dissociate in water, resulting in a higher concentration of H+ ions, while weak acids only partially dissociate. The pH at the equivalence point can indicate the strength of the acid; a higher pH suggests a weaker acid, while a lower pH indicates a stronger acid.

pH Scale and Acid-Base Behavior

The pH scale measures the acidity or basicity of a solution, ranging from 0 (very acidic) to 14 (very basic), with 7 being neutral. In the context of titrations, the pH at the equivalence point helps to classify the acid's strength. For the acids in this question, the pH values indicate that acid A, with the highest pH at equivalence, is the weakest, while acid C, with the lowest pH, is the strongest.