Describe how to perform a titration to determine the concentration of a monoprotic acid and identify the equivalence point.

• A. Detect the equivalence point with a color change of the indicator.
• B. Equivalence point occurs when moles of acid added equal moles of base.
• C. Equivalence point occurs when pH equals 7.
• D. Equivalence point occurs when the base color changes indicators.

Answer: (B)

Equivalence in a titration is defined by equal moles of reactants in the stoichiometric reaction. For a monoprotic acid, that means the moles of acid present have to equal the moles of base added.

To perform it, place a known volume of the monoprotic acid in a flask and fill a burette with a base of known concentration. Record the acid’s initial volume, then add the base gradually with swirling, monitoring the reaction with an indicator or a pH meter. The moment you reach the equivalence point is when the acid and base have reacted in a 1:1 ratio, so the number of moles of acid equals the number of moles of base added.

You can use the relationship n_acid = n_base to calculate the acid concentration: C_acid = (C_base × V_base at equivalence) / V_acid. Note that the pH at equivalence isn’t always 7; it depends on the strengths of the acid and base. An appropriate indicator is chosen so its color change occurs near the equivalence pH, helping you detect the endpoint as a practical signal of that stoichiometric point.