The equivalence point occurs when:

The equivalence point occurs when:

• A. The pH equals 7.
• B. The moles of OH- added equal the initial moles of HA.
• C. Half of HA is neutralized.
• D. All A- is converted back to HA.

Answer: (B)

The main idea tested is when the titration reaches a point where the added base has exactly neutralized all the acid present. For a weak acid being titrated with a strong base, the neutralization is HA + OH- → A- + H2O, and the equivalence point occurs precisely when the moles of OH- added equal the initial moles of HA. At that moment, all the acid has been converted to its conjugate base, and the pH is determined by the hydrolysis of that base, which is usually basic rather than neutral. This is why the statement about equal moles of OH- and HA is the best description of the equivalence point. The idea that the pH must be 7 applies only to strong acid–strong base titrations, not typical weak acid–strong base cases. The notion of half of the acid being neutralized corresponds to the half-equivalence point, not the equivalence point. And the idea that all conjugate base is converted back to the acid describes reversing the reaction or proceeding beyond equivalence, not the equivalence condition itself.

The main idea tested is when the titration reaches a point where the added base has exactly neutralized all the acid present. For a weak acid being titrated with a strong base, the neutralization is HA + OH- → A- + H2O, and the equivalence point occurs precisely when the moles of OH- added equal the initial moles of HA. At that moment, all the acid has been converted to its conjugate base, and the pH is determined by the hydrolysis of that base, which is usually basic rather than neutral.

This is why the statement about equal moles of OH- and HA is the best description of the equivalence point. The idea that the pH must be 7 applies only to strong acid–strong base titrations, not typical weak acid–strong base cases. The notion of half of the acid being neutralized corresponds to the half-equivalence point, not the equivalence point. And the idea that all conjugate base is converted back to the acid describes reversing the reaction or proceeding beyond equivalence, not the equivalence condition itself.