Potassium Hydroxide
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| Names | |
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IUPAC name
Potassium hydroxide
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| Other names
Caustic potash, Lye, Potash lye, Potassia, Potassium hydrate, KOH
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| Identifiers | |
1310-58-3 
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| 3D model (Jmol) | Interactive image |
| ChEBI |
CHEBI:32035
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| ChemSpider |
14113
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| ECHA InfoCard | 100.013.802 |
| EC Number | 215-181-3 |
| E number | E525 (acidity regulators, ...) |
| PubChem | 14797 |
| RTECS number | TT2100000 |
| UNII |
WZH3C48M4T
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| UN number | 1813 |
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| Properties | |
| 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) |
| 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) |
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| 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–) |
| −22.0·10−6 cm3/mol | |
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Refractive index (nD)
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1.409 (20 °C) |
| Structure | |
| rhombohedral | |
| Thermochemistry | |
| 65.87 J/mol·K | |
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Std molar
entropy (S |
79.32 J/mol·K |
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Std enthalpy of
formation (ΔfH |
-425.8 kJ/mol |
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Gibbs free energy (ΔfG˚)
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-380.2 kJ/mol |
| Hazards | |
| Safety data sheet | ICSC 0357 |
| GHS pictograms |
 
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| GHS signal word | Danger |
| H302, H314 | |
| P280, P305+351+338, P310 | |
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EU classification (DSD)
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 C  Xn
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| R-phrases | R22, R35 |
| S-phrases | (S1/2), S26, S36/37/39, S45 |
| NFPA 704 | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
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LD50 (median dose)
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273 mg/kg (oral, rat) |
| US health exposure limits (NIOSH): | |
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PEL (Permissible)
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none |
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REL (Recommended)
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C 2 mg/m3 |
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IDLH (Immediate danger)
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N.D. |
| Related compounds | |
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Other anions
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Potassium hydrosulfide Potassium amide |
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Other cations
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Lithium hydroxide Sodium hydroxide Rubidium hydroxide Caesium hydroxide |
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Related compounds
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Potassium oxide |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is  ?) |
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| 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.
...
Wikipedia