characteristics of khp that make it qualify as a primary standard
Potassium hydrogen phthalate 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. KHP is slightly acidic, and it is often used as a primary standard for acid-base titrations because it is solid and air-stable, making it easy to weigh accurately. It is not hygroscopic.[2][3][4] It is also 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[5].