Which term describes a substance with a known concentration used for standardization in titration procedures?

• A. Endpoint
• B. Equivalence point
• C. Primary standard
• D. Titrant

Answer: (C)

For titration, you need a solution with a precisely known concentration so you can determine how much analyte is present. That role is filled by a primary standard. A primary standard is a reagent of very high purity that can be weighed accurately, dissolved to make a standard solution, and has a well-defined stoichiometry. Because it’s stable and non-hygroscopic, its mass directly translates to moles, giving an exact concentration for standardizing the titrant. This allows you to calculate the analyte’s concentration from the titration data. For example, potassium hydrogen phthalate is often used to standardize NaOH solutions. The endpoint, equivalence point, and titrant describe other parts of the titration process, not a substance with a known concentration used for standardization.