Caustic potash

Potassium hydroxide

Names
IUPAC name Potassium hydroxide
Other names Caustic potash, Lye, Potash lye, Potassia, Potassium hydrate, KOH
Identifiers
CAS Number	1310-58-3 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:32035 Y
ChemSpider	14113 Y
ECHA InfoCard	100.013.802
EC Number	215-181-3
E number	E525 (acidity regulators, ...)
PubChem	14797
RTECS number	TT2100000
UNII	WZH3C48M4T Y
UN number	1813
InChI InChI=1S/K.H2O/h;1H2/q+1;/p-1 Y Key: KWYUFKZDYYNOTN-UHFFFAOYSA-M Y InChI=1/K.H2O/h;1H2/q+1;/p-1 Key: KWYUFKZDYYNOTN-REWHXWOFAT
SMILES [K+].[OH-]
Properties
Chemical formula	KOH
Molar mass	56.11 g mol−1
Appearance	white solid, deliquescent
Odor	odorless
Density	2.044 g/cm3 (20 °C) 2.12 g/cm3 (25 °C)
Melting point	360 °C (680 °F; 633 K)
Boiling point	1,327 °C (2,421 °F; 1,600 K)
Solubility in water	85 g/100 g (-23.2 °C) 97 g/100 mL (0 °C) 121 g/100 mL (25 °C) 138.3 g/100 mL (50 °C) 162.9 g/100 mL (100 °C)
Solubility	soluble in alcohol, glycerol insoluble in ether, liquid ammonia
Solubility in methanol	55 g/100 g (28 °C)
Solubility in isopropanol	~14 g / 100 g (28 °C)
Basicity (pKb)	−0.7(KOH(aq) = K+ + OH–)
Magnetic susceptibility (χ)	−22.0·10−6 cm3/mol
Refractive index (nD)	1.409 (20 °C)
Structure
Crystal structure	rhombohedral
Thermochemistry
Specific heat capacity (C)	65.87 J/mol·K
Std molar entropy (So298)	79.32 J/mol·K
Std enthalpy of formation (ΔfHo298)	-425.8 kJ/mol
Gibbs free energy (ΔfG˚)	-380.2 kJ/mol
Hazards
Safety data sheet	ICSC 0357
GHS pictograms
GHS signal word	Danger
GHS hazard statements	H302, H314
GHS precautionary statements	P280, P305+351+338, P310
EU classification (DSD)	C Xn
R-phrases	R22, R35
S-phrases	(S1/2), S26, S36/37/39, S45
NFPA 704	0 3 1
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	273 mg/kg (oral, rat)
US health exposure limits (NIOSH):
PEL (Permissible)	none
REL (Recommended)	C 2 mg/m3
IDLH (Immediate danger)	N.D.
Related compounds
Other anions	Potassium hydrosulfide Potassium amide
Other cations	Lithium hydroxide Sodium hydroxide Rubidium hydroxide Caesium hydroxide
Related compounds	Potassium oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Potassium hydroxide is an inorganic compound with the formula KOH, and is commonly called caustic potash.

Along with sodium hydroxide (NaOH), this colorless solid is a prototypical strong base. It has many industrial and niche applications, most of which exploit its corrosive nature and its reactivity toward acids. An estimated 700,000 to 800,000 tonnes were produced in 2005. Approximately 100 times more NaOH than KOH is produced annually. KOH is noteworthy as the precursor to most soft and liquid soaps as well as numerous potassium-containing chemicals.

Potassium hydroxide can be found in pure form by reacting sodium hydroxide with impure potassium. It is usually sold as translucent pellets, which will become tacky in air because KOH is hygroscopic. Consequently, KOH typically contains varying amounts of water (as well as carbonates, see below). Its dissolution in water is strongly exothermic. Concentrated aqueous solutions are sometimes called potassium lyes. Even at high temperatures, solid KOH does not dehydrate readily.

Potassium hydroxide solutions with concentrations of approximately 0.5 to 2.0% are irritating when coming into contact with the skin, while concentrations higher than 2% are corrosive.

At higher temperatures, solid KOH crystallizes in the NaCl crystal structure. The OH group is either rapidly or randomly disordered so that the OH−
group is effectively a spherical anion of radius 1.53 Å (between Cl−
and F−
in size). At room temperature, the OH−
groups are ordered and the environment about the K+
centers is distorted, with K+
—OH−
distances ranging from 2.69 to 3.15 Å, depending on the orientation of the OH group. KOH forms a series of crystalline hydrates, namely the monohydrate KOH·H
2O, the dihydrate KOH·2 H
2O, and the tetrahydrate KOH·4 H
2O.