What is Sodium Phosphate Monobasic?

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An important chemical in your body, sodium phosphate monobasic also possesses properties highly desired in a variety of laboratory experiments. Working in tandem with sodium phosphate dibasic, this buffering solution helps control rapid fluctuations in pH, both in your body and in laboratory experiments. While it can be toxic, especially in combination with other drugs, sodium phosphate solutions help relieve symptoms of constipation.


Chemically, the formula for sodium phosphate monobasic consists of one sodium or Na atom, two hydrogen or H atoms, and one phosphate or PO4 group. The monohydrate form also has one associated water or H2O molecule for every molecule of sodium phosphate monobasic, or NaH2PO4+H2O. The term monobasic refers to the neutralization of the molecule by a single or univalent base group. When dissolved in solution, a single base group will neutralize the dissociated sodium atom. By contrast, the dibasic form of sodium phosphate having the formula Na2HPO4 +2H2O, dissociates into two sodium atoms when dissolved, requiring two basic groups to neutralize them.

Physical Properties

Sodium phosphate monobasic exists as a white, odorless, crystalline powder. Slightly acidic, sodium phosphate monobasic has a pH of 4.5. The dissociated H2PO4 group has only one negative net negative charge, requiring only one hydrogen to neutralize the molecule. In contrast, the dibasic version has a much higher pH of 9.5 by virtue of the dissociated HPO4 group having a net negative charge of 2, requiring much more acid to neutralize that group. In addition, sodium phosphate monobasic boils at 399 degrees F and melts at 212 degrees F.

Buffering Agent

Sodium phosphate monobasic acts as a buffering agent, preventing the pH of a solution from changing when challenged by an acid or a base. Sodium phosphate buffers exist in all cellular fluids. Dihydrogen phosphate or H2PO4- ions act as acids while the hydrogen phosphate or HPO4 ions act as bases. These two ions are in equilibrium with each other keeping cellular fluids in a tight pH range of about 6.9 to 7.4.


Sodium phosphate monobasic, in combination with sodium phosphate dibasic acts as a laxative, inducing bowel movements. As a pharmaceutical agent, this combination helps those suffering from constipation, or as a prescription to help completely empty your bowels before surgery or other medical procedure. Side effects of this medication include potential for allergic reactions, decreased urination, dizziness, fainting, dry mouth, seizures, severe stomach pain, nausea, vomiting and bloating, red or black stools and an irregular heart rhythm.


As a pure chemical, sodium phosphate monobasic irritates your skin, eyes and respiratory tract, and can be harmful if swallowed or inhaled. Phosphate buffer laxatives should not be combined with other medicines without consulting a health professional. Negative reactions could result if taken in combination with drugs designed to lower blood pressure, treat depression, or manage pain, or if you are pregnant or breastfeeding, having kidney or heart or electrolyte problems or a history of seizures.