A method for determining the concentration of an acid (or base) by neutralization of a known volume of that acid (or base) with a known volume of base (or acid) at a known concentration.

• A. Buffer Solution
• B. pH
• C. Strong acid (or base)
• D. Titration

Answer: (D)

This item tests the method used to determine concentration by neutralization, where a known volume of the acid or base (the analyte) is reacted with a solution of known concentration (the titrant) until neutralization is complete. That method is titration. In a titration, you add the titrant gradually to the analyte and use the point at which the reaction is complete (the equivalence point) to calculate the unknown concentration, using the known volumes and the stoichiometry of the reaction, typically expressed as M1V1 = M2V2 for the balanced equation.

Practically, you’ll detect the endpoint with an indicator that changes color (or with a pH meter) at a pH appropriate for the equivalence point, so you know when to stop and perform the calculation. This approach works for both acids and bases and is widely used because it ties measurable quantities (volumes and known concentration) to the unknown concentration.

The other ideas describe either substances or concepts that don’t provide a procedure for determining concentration by neutralization: a buffer resists pH change and isn’t a method for finding concentration; pH is a measurement of acidity, not a determination method; and describing a strong acid or base refers to strength, not to how you quantify concentration.