Sodium Phosphate, Monobasic, Monohydrate (10049-21-5) Physical and Chemical Properties
Sodium Phosphate, Monobasic, Monohydrate
Monobasic sodium phosphate monohydrate is an inorganic buffering salt commonly used for pH control, buffer preparation and formulation in industrial, laboratory and pharmaceutical manufacturing contexts.
| CAS Number | 10049-21-5 |
| Family | Metallic phosphates |
| Typical Form | White crystalline solid (monohydrate) |
| Common Grades | EP, Reagent Grade, Technical Grade |
Sodium phosphate monobasic monohydrate is an inorganic ionic salt in the phosphate family, formally the monosodium salt of phosphoric acid with one equivalent of water of crystallization. Structurally it exists as the hydrated ionic assembly containing the sodium cation and the dihydrogen phosphate anion together with a lattice water molecule; the empirical formula is \(\ce{H4NaO5P}\). Electronically the anionic component \(\ce{H2PO4^-}\) is a tetrahedral oxoanion of phosphorus (formally PO4) bearing one acidic proton; the overall solid is held by ionic interactions and an extended hydrogen-bond network that includes the water of hydration.
The compound behaves as a water‑soluble inorganic salt that generates acidic aqueous solutions due to the presence of the dihydrogen phosphate anion, and it functions routinely as a weakly acidic component in phosphate buffer systems. It is polar and hygroscopic (slightly deliquescent), with strong hydrogen-bond donor and acceptor capability arising from the dihydrogen phosphate and water constituents, which underpins its high aqueous solubility and common use in wet‑chemistry and biological applications. Oxidative degradation is not a relevant pathway under normal handling; hydrolysis simply reflects the acid–base equilibria of the phosphate system rather than covalent bond scission.
Common commercial grades reported for this substance include: EP, Reagent Grade, Technical Grade.
Basic Physical Properties
Density
No experimentally established value for this property is available in the current data context.
Melting or Decomposition Point
No experimentally established value for this property is available in the current data context.
Solubility in Water
Sodium phosphate monobasic monohydrate is readily soluble in water as an ionic salt; dissolution produces free \(\ce{Na+}\), \(\ce{H2PO4^-}\), and solvent water. The solid is described as slightly deliquescent and hygroscopic, consistent with strong ion–dipole interactions and an extensive hydrogen-bonding network in the hydrated lattice. Solubility behaviour is dominated by ionic dissociation and the subsequent phosphate acid–base equilibria in the aqueous phase.
Solution pH (Qualitative Behavior)
In aqueous solution the dominant anion is \(\ce{H2PO4^-}\), so solutions are acidic relative to neutral water and can act as the acidic component of phosphate buffer systems. The substance therefore serves as a pH‑adjusting and buffering reagent in acidic to near‑neutral formulations when combined with appropriate quantities of the conjugate base (\(\ce{HPO4^2-}\)).
Chemical Properties
Acid–Base Behavior
As the monosodium salt of phosphoric acid, the primary dissolved species is \(\ce{H2PO4^-}\), which retains an acidic proton and can donate a proton in solution (acting as an acid) or accept one via the phosphate equilibria when paired with stronger acids or bases. This makes the compound useful as a buffering agent in systems where control of acidity in the mildly acidic range is required. The solid is the hydrated form and will release water upon drying or under elevated temperature, reverting to lower hydration states or the anhydrous salt under appropriate conditions.
Reactivity and Stability
The material is chemically stable under normal laboratory and industrial storage conditions if kept dry and protected from atmospheric moisture. It is not prone to oxidative decomposition; chemical reactivity is dominated by acid–base interactions and salt metathesis (ion exchange) with other cations or anions. Contact with strong bases will convert \(\ce{H2PO4^-}\) to more basic phosphate species, while concentrated acids will protonate phosphate to phosphoric acid forms. The hydrated solid will adsorb moisture from humid air (hygroscopic/deliquescent behaviour).
Molecular and Ionic Parameters
Formula and Molecular Weight
- Molecular formula: \(\ce{H4NaO5P}\)
- Molecular weight: 137.99 (as reported)
Constituent Ions
The solid is properly described as a hydrated ionic assembly composed of:
- sodium cation: \(\ce{Na+}\)
- dihydrogen phosphate anion: \(\ce{H2PO4^-}\)
- water of crystallization: \(\ce{H2O}\)
These constituent units give rise to an ionic crystal stabilized by electrostatic interactions and hydrogen bonding.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS Number: 10049-21-5
- EC Number: 600-102-0
- UNII: 593YOG76RN
- ChEBI: CHEBI:114249
- InChIKey:
BBMHARZCALWXSL-UHFFFAOYSA-M - InChI:
InChI=1S/Na.H3O4P.H2O/c;1-5(2,3)4;/h;(H3,1,2,3,4);1H2/q+1;;/p-1 - SMILES:
O.OP(=O)(O)[O-].[Na+]
Synonyms and Common Names
Common synonyms and alternative names reported for this substance include (selection): Sodium phosphate monobasic monohydrate; Sodium dihydrogen phosphate monohydrate; Monosodium phosphate monohydrate; Phosphoric acid, monosodium salt, monohydrate; Sodium phosphate monohydrate; sodium dihydrogenphosphate monohydrate; H4NaO5P.
Industrial and Commercial Applications
Functional Roles and Use Sectors
Sodium phosphate monobasic monohydrate is used widely as an acidulant, sequestrant, buffering agent, and source of phosphate in food, formulation and industrial applications. It is employed in food processing (acidulant/sequestrant), some baking powder formulations, water treatment (e.g., boiler water conditioning as a phosphate source), veterinary products (urinary acidifier), and as a component or excipient in various pharmaceutical formulations. In laboratory and bioprocess settings it is used as a reagent and buffer component for biochemical and molecular biology workflows.
Typical Application Examples
Representative uses include:
- Component in phosphate buffer systems for biochemical assays and cell culture media (used in combination with dibasic phosphate salts to set target \( \mathrm{pH} \)).
- Acidulant and sequestrant in food and feed formulations.
- Boiler water and industrial water treatment as a phosphate additive.
- Component in certain pharmaceutical product formulations and veterinary preparations.
- Reagent‑grade material for analytical chemistry and molecular biology applications; cell culture and molecular biology grades are commercially available for laboratory use.
If a concise application summary is required but not available in the present data context, in practice this substance is selected based on its high aqueous solubility, buffering behavior, and low organic reactivity as described above.
Safety and Handling Overview
Health and Environmental Hazards
The substance is generally classified as an irritant under typical hazard-labeling schemes: it can cause skin and eye irritation and may cause respiratory tract irritation if dust is inhaled. Reported hazard statements associated with handling include codes for skin irritation (e.g., H315), serious eye irritation (H319), and possible respiratory irritation (H335) in notifications from manufacturers and regulatory filings. The solid is described as white, odorless, and slightly deliquescent; dust generation should be minimized to reduce inhalation exposure.
Storage and Handling Considerations
Store in tightly closed containers in a cool, dry, well‑ventilated area to prevent uptake of moisture and caking. Protect from humidity and sources of contamination. Use appropriate engineering controls and personal protective equipment: dust control, eye protection, chemical‑resistant gloves, and respiratory protection where dusting or aerosolization is possible. Avoid contact with strong bases and reactive metals where salt metathesis or other undesired reactions could occur. For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
