KHP

KHP stands for potassium hydrogen phthalate, a white crystalline inorganic salt with the chemical formula KHC8H4O4 (and commonly encountered as the monohydrate form, KHP·H2O). It is widely used as a primary standard in acid–base chemistry because of its high purity, stability, and relatively low hygroscopicity, which allow accurate preparation of standard solutions.

As a primary standard, KHP enables precise determination of the concentration of base solutions such as sodium hydroxide. In typical practice, a weighed sample of known mass is dissolved in water to prepare a solution with a known amount of substance per liter. The solution is then titrated against the base of unknown concentration, and the base concentration is calculated from the reaction stoichiometry and the weighed mass of KHP. The molar mass of the anhydrous form is about 204.22 g/mol, a value used in calculations; when water of crystallization is present, its mass must be accounted for.

KHP is also used in pH meter calibration and in preparing buffer solutions for reference measurements, due to its well-defined acid-base properties and stable behavior under typical laboratory conditions.

Handling and storage: KHP should be kept in a dry, tightly sealed container to minimize moisture uptake and contamination. It is considered to have low toxicity, but as with many chemical solids, inhalation of dust or ingestion should be avoided; standard laboratory hygiene applies, including gloves and eye protection as appropriate.

See also: primary standard, acid–base titration, pH calibration.