Potassium hydrogen phthalate, often called simply KHP, is an acidic salt compound. It forms white powder, colorless crystals, a colorless solution, and an ionic solid that is the monopotassium salt of phthalic acid.
P 2265 (OTTO) Potassium hydrogen phthalate, 99% Cas 877-24-7 - used as a primary standard for calibrating pH meters because, besides the properties just mentioned, its pH in solution is very stable. It also serves as a thermal standard in thermogravimetric analysis.