Dipotassium hydrogenphosphate
[CAS 7758-11-4]

Identification

• Classification: API >> Water, electrolyte and acid-base balance regulator >> Acid-base balance regulator
• Name: Dipotassium hydrogenphosphate
• Synonyms: Potassium phosphate dibasic
• Molecular Formula: K₂HPO₄
• Molecular Weight: 174.17
• CAS Registry Number: 7758-11-4
• EC Number: 231-834-5
• SMILES: OP(=O)([O-])[O-].[K+].[K+]

Properties

• Melting point: 465 (Decomposes) °C (Expl.)
• Solubility: Soluble in water (Expl.)

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Risk Statements: H315-H318
• Safety Statements: P264-P264+P265-P280-P302+P352-P305+P354+P338-P317-P321-P332+P317-P362+P364

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H302
Skin corrosion	Skin Corr.	1A	H314
Eye irritation	Eye Irrit.	2	H319

chemBlink Chemical Story

Dipotassium hydrogenphosphate is one of those laboratory chemicals whose importance comes less from a dramatic reaction than from its ability to hold chemical conditions steady. With the formula K₂HPO₄, it is the dipotassium salt of phosphoric acid in which the dominant phosphate species is hydrogen phosphate, HPO₄^2-. In water it participates in the H₂PO₄^-/HPO₄^2- acid-base pair, one of the most familiar buffering systems in chemistry and biology.

A buffer does not make pH absolutely constant. Instead, a conjugate acid-base pair absorbs moderate additions of acid or base so that proton activity changes much less than it otherwise would. The second dissociation of phosphoric acid lies near neutral pH, making mixtures of monobasic and dibasic phosphate especially useful around the conditions encountered in biochemical experiments. Dipotassium hydrogenphosphate supplies the basic member of that pair while introducing potassium rather than sodium as the counterion. This can matter when ionic composition, enzyme activity, cell physiology, or downstream crystallization is sensitive to the identity and concentration of alkali-metal ions.

The compound is therefore common in buffer preparation, fermentation media, biochemical work, and formulations in which phosphate also supplies phosphorus and potassium. Yet phosphate is not chemically invisible. It can interact strongly with calcium and magnesium, precipitate poorly soluble phosphates, bind to mineral surfaces, and alter the behavior of proteins or metal-dependent enzymes. A phosphate buffer that is ideal for one experiment may be a poor choice for another. Good laboratory practice treats the buffer as a chemical participant, not merely as a background number on a pH meter.

Solid-state identity matters as well. Reagent specifications distinguish assay, water content, insoluble matter, sodium contamination, and the pH of standardized solutions. Accurate preparation depends on using the correct formula mass and material grade. This is particularly important when comparing anhydrous phosphate salts with hydrates, because crystal water changes the mass required to deliver the same number of phosphate equivalents.

Dipotassium hydrogenphosphate matters because it illustrates a quiet but fundamental role of chemistry: creating a reproducible environment in which other chemistry can occur. Enzymes, cells, analytical reactions, and manufacturing processes often work only inside a narrow pH and ionic window. K₂HPO₄ helps define that window. Its apparent simplicity is precisely why it is easy to overlook the deeper lesson: controlling conditions is often as important as choosing the main reactants.

References:
ACS Reagent Chemicals. Potassium Phosphate, Dibasic. DOI: 10.1021/acsreagents.4304.20251001.
Cold Spring Harbor Protocols. Phosphate-buffered saline and phosphate buffer preparations. DOI: 10.1101/pdb.rec8543.
Good NE et al. Biochemistry. 1966;5:467-477. DOI: 10.1021/bi00866a011.

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