Sodium Hydroxide
Sodium Hydroxide is a highly alkaline ingredient used in small amounts in cosmetics to establish and hold the pH of a product. It’s other common names are lye or caustic soda and in pure form or high concentrations, it’s a significant skin sensitizer. However, the very small amounts necessary to balance pH in cosmetics is generally considered safe.
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations Na+ and hydroxide anions OH−.
| |
| |
| Names | |
|---|---|
| IUPAC name
Sodium hydroxide
| |
Other names
| |
| Identifiers | |
3D model (JSmol)
|
|
| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.013.805 |
| EC Number |
|
| E number | E524 (acidity regulators, ...) |
| 68430 | |
| KEGG | |
| MeSH | Sodium+Hydroxide |
PubChem CID
|
|
| RTECS number |
|
| UNII | |
| UN number | 1824, 1823 |
CompTox Dashboard (EPA)
|
|
| |
| |
| Properties | |
| NaOH | |
| Molar mass | 39.9971 g/mol |
| Appearance | White, hard (when pure), opaque crystals |
| Odor | odorless |
| Density | 2.13 g/cm3 |
| Melting point | 323 °C (613 °F; 596 K) |
| Boiling point | 1,388 °C (2,530 °F; 1,661 K) |
| 418 g/L (0 °C) 1000 g/L (25 °C) 3370 g/L (100 °C) | |
| Solubility | soluble in glycerol, negligible in ammonia, insoluble in ether, slowly soluble in propylene glycol |
| Solubility in methanol | 238 g/L |
| Solubility in ethanol | <<139 g/L |
| Vapor pressure | <2.4 kPa (at 20 °C) |
| Acidity (pKa) | 15.7 |
| −15.8·10−6 cm3/mol (aq.) | |
Refractive index (nD)
|
1.3576 |
| Structure | |
| Orthorhombic, oS8 | |
| Cmcm, No. 63 | |
a = 0.34013 nm, b = 1.1378 nm, c = 0.33984 nm
| |
Formula units (Z)
|
4 |
| Thermochemistry | |
Heat capacity (C)
|
59.5 J/(mol·K) |
Std molar
entropy (S⦵298) |
64.4 J/(mol·K) |
Std enthalpy of
formation (ΔfH⦵298) |
−425.8 kJ/mol |
Gibbs free energy (ΔfG⦵)
|
-379.7 kJ/mol |
| Hazards | |
| GHS labelling: | |
| |
| Danger | |
| H290, H314 | |
| P280, P305+P351+P338, P310 | |
| NFPA 704 (fire diamond) | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
|
40 mg/kg (mouse, intraperitoneal) |
LDLo (lowest published)
|
500 mg/kg (rabbit, oral) |
| NIOSH (US health exposure limits): | |
PEL (Permissible)
|
TWA 2 mg/m3 |
REL (Recommended)
|
C 2 mg/m3 |
IDLH (Immediate danger)
|
10 mg/m3 |
| Safety data sheet (SDS) | External SDS |
| Related compounds | |
Other anions
|
|
Other cations
|
|
Related compounds
|
Sodium deuteroxide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Sodium hydroxide is a highly caustic base and alkali that decomposes proteins at ordinary ambient temperatures and may cause severe chemical burns. It is highly soluble in water, and readily absorbs moisture and carbon dioxide from the air. It forms a series of hydrates NaOH·nH2O. The monohydrate NaOH·H2O crystallizes from water solutions between 12.3 and 61.8 °C. The commercially available "sodium hydroxide" is often this monohydrate, and published data may refer to it instead of the anhydrous compound.
As one of the simplest hydroxides, sodium hydroxide is frequently used alongside neutral water and acidic hydrochloric acid to demonstrate the pH scale to chemistry students.
Sodium hydroxide is used in many industries: in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents, and as a drain cleaner. Worldwide production in 2004 was approximately 60 million tons, while demand was 51 million tons.
