What is a primary standard and how is it used in titrations?

A primary standard is a highly pure, stable substance used to determine the concentration of a solution in titrations.

In more detail, a primary standard is a substance of known purity and composition. It is used in analytical chemistry, particularly in titrations, to accurately determine the concentration of an unknown solution. The primary standard must meet several criteria to be effective. It must be highly pure, stable in air, have a known formula, and react completely and specifically with the solution being tested.

In a titration, a solution of the primary standard, known as the titrant, is gradually added to the solution being tested, or the analyte. The point at which the reaction between the two is complete is known as the equivalence point. This is often determined by a sudden change in the colour of the solution, caused by an indicator. By knowing the volume of titrant needed to reach the equivalence point and the concentration of the titrant, the concentration of the analyte can be calculated.

Primary standards are crucial in titrations as they provide a reference point for measurements. They ensure that the results of the titration are accurate and reliable. Examples of substances often used as primary standards include sodium chloride for silver nitrate titrations, and potassium hydrogen phthalate for acid-base titrations.

In summary, a primary standard is a key tool in titrations, providing a benchmark for determining the concentration of an unknown solution. Its high purity and stability ensure the accuracy and reliability of the titration results.