Potassium hydroxide

Athanor · official

HKO · 56.106 g/mol

Also called caustic potash, KOH, E525

Inorganic

Open in Athanor

Drawn from its SMILES with RDKit

DangerHarmful if swallowed · Causes severe skin burns and eye damage

Names and identifiers

IUPAC name: potassium hydroxide
Synonyms: caustic potash, KOH, E525
+ 37 more
Caustic potash, Potash lye, Potassium hydrate, Hydroxyde de potassium, Potassa, Potasse caustique, Caustic-potash, Kali causticum, Caswell No. 693, Cyantek CC 723, Potassium hydroxide (K(OH)), Kaliumhydroxid, CCRIS 6569, Potassio (idrossido di), Potassium (hydroxyde de), WZH3C48M4T, EPA Pesticide Chemical Code 075602, INS NO.525, INS-525, DTXSID5029633, E-525, CHEBI:32035, Kaliumhydroxyde, RefChem:6672, MIRACLE WATER 3 in 1, DTXCID209633, 215-181-3, potassium;hydroxide, Potassium hydroxide, pellets, MFCD00003553, Potassium hydroxide, flake, Potassium Hydroxide (~85%), potassiumhydroxide, Potasse caustique [French], Potassium hydroxide [JAN], Potassium Hydroxide (Semiconductor Grade), Hydroxyde de potassium [French]
Molecular formula: HKO
Empirical formula: HKO
Molecular weight: 56.106 g/mol
Exact mass: 55.96645
CAS number: 1310-58-3
PubChem CID: 14797
Canonical SMILES: [OH-].[K+]
Isomeric SMILES: [OH-].[K+]
InChI: InChI=1S/K.H2O/h;1H2/q+1;/p-1
InChIKey: KWYUFKZDYYNOTN-UHFFFAOYSA-M
Molfile

Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.

Physical properties

TemperaturePressureDensity

Appearance: White or colorless, orthorhombic, deliquescent pieces, lumps, or sticks having crystalline fracture[6]
7 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source
– Potassium hydroxide, solution appears as an clear aqueous solution. Corrosive to metals and tissue. Noncombustible. Used in chemical manufacturing, petroleum refining, cleaning compounds. [1] CAMEO Chemicals
– Potassium hydroxide, [dry solid, flake, bead, or granular] appears as a white solid. Corrosive to metals and tissue. Used in soap manufacture, bleach, as an electrolyte in alkaline batteries, and as a food additive. [1] CAMEO Chemicals
– Liquid; Dry Powder; Liquid; Liquid; Other Solid; Dry Powder; Large Crystals; Large Crystals; CBI; Dry Powder; Other Solid [2] EPA Chemical Data Reporting (CDR)
– WHITE HYGROSCOPIC SOLID IN VARIOUS FORMS. [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– White, odorless solid or clear aqueous solution. [4] Occupational Safety and Health Administration (OSHA)
– Odorless, white or slightly yellow lumps, rods, flakes, sticks, or pellets. [Note: May be used as an aqueous solution.] [5] The National Institute for Occupational Safety and Health (NIOSH)
–shown White or colorless, orthorhombic, deliquescent pieces, lumps, or sticks having crystalline fracture [6] Hazardous Substances Data Bank (HSDB)cites Lewis, R.J. Sr. (ed) Sax's Dangerous Properties of Industrial Materials. 12th Edition. Wiley-Interscience, Wiley & Sons, Inc. Hoboken, NJ. 2012., p. 3730
Odor: Odorless[6]
Melting point: 380 °C[3]
5 values
2 of 5 sources agree on it (most common value).
Value As written Source
360 °C 680 °F approximately (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
380 °Cshown 380 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
360 °C 680 °F [4] Occupational Safety and Health Administration (OSHA)
406 °C 406 °C [7] PAC Chemical Database, U.S. Department of Energy
380 °C 716 °F [5] The National Institute for Occupational Safety and Health (NIOSH)
3 more values were reported but failed the checks (unreadable or out of range), so they are not shown.
Boiling point: 1324 °C[3]
5 values
2 of 5 sources agree on it (most common value).
Value As written Source
1320 °C 2408 °F at 760 mmHg (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
1324 °Cshown 1324 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
1320 °C 2408 °F [4] Occupational Safety and Health Administration (OSHA)
1327 °C 1327 °C @760 [mm Hg] [7] PAC Chemical Database, U.S. Department of Energy
1324 °C 2415 °F [5] The National Institute for Occupational Safety and Health (NIOSH)
1 more value was reported but failed the checks (unreadable or out of range), so it is not shown.
Density: 2.044 @25 °C[7]
8 values
5 of 6 sources agree on it (most common value).
Value As written Source
– 1.45 to 1.50 at 68 °F (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
– 2.04 at 59 °F (USCG, 1999) - Denser than water [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
– 1.188 at 29 [6] Hazardous Substances Data Bank (HSDB)cites Schultz H et al; Potassium Compounds. Ullmann's Encyclopedia of Industrial Chemistry. 7th ed. (1999-2015). New York, NY: John Wiley & Sons. Online Posting Date: a5 Jun 2000
– 1.514 at 50 /Aqueous potassium hydroxide/ [6] Hazardous Substances Data Bank (HSDB)cites Schultz H et al; Potassium Compounds. Ullmann's Encyclopedia of Industrial Chemistry. 7th ed. (1999-2015). New York, NY: John Wiley & Sons. Online Posting Date: a5 Jun 2000
– 2.04 g/cm³ [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– 2.04 [4] Occupational Safety and Health Administration (OSHA)
–shown 2.044 @25 °C [7] PAC Chemical Database, U.S. Department of Energy
– 2.04 [5] The National Institute for Occupational Safety and Health (NIOSH)
3 more values were reported but failed the checks (unreadable or out of range), so they are not shown.
Solubility in water: Solubility in water, g/100ml at 25 °C: 110 (very good)[3]
5 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source
– 107 g/100 cc at 59 °F (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
– Solubility in water (g KOH/100 g H2O): 97 at 0 °C; 103 at 10 °C; 112 at 20 °C; 126 at 30 °C; 178 at 100 °C [6] Hazardous Substances Data Bank (HSDB)cites Schultz H et al; Potassium Compounds. Ullmann's Encyclopedia of Industrial Chemistry. 7th ed. (1999-2015). New York, NY: John Wiley & Sons. Online Posting Date: a5 Jun 2000
– For more Solubility (Complete) data for POTASSIUM HYDROXIDE (6 total), please visit the HSDB record page. [6] Hazardous Substances Data Bank (HSDB)
–shown Solubility in water, g/100ml at 25 °C: 110 (very good) [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– (59 °F): 107% [5] The National Institute for Occupational Safety and Health (NIOSH)
Vapor pressure: 1 MM HG @ 714 °C[6]
5 values
3 of 3 sources agree on it (most common value).
Value As written Source
1 mmHg 1 mmHg at 1326 °F [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
5 mmHg 5 mmHg at 1497 °F (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
1 mmHgshown 1 MM HG @ 714 °C [6] Hazardous Substances Data Bank (HSDB)cites Sax, N.I. Dangerous Properties of Industrial Materials. 6th ed. New York, NY: Van Nostrand Reinhold, 1984., p. 1047
1 mmHg 1 mmHg at 1326 °F [4] Occupational Safety and Health Administration (OSHA)
5 mmHg 5 mmHg at 1497 °F [4] Occupational Safety and Health Administration (OSHA)
1 more value was reported but failed the checks (unreadable or out of range), so it is not shown.
Autoignition temperature: Reported, but no value passed the checks.
The 2 values and why
Not flammable (USCG, 1999) (could not be read; source [1])
Not flammable (USCG, 1999) (could not be read; source [1])

Value	As written	Source
–	Potassium hydroxide, solution appears as an clear aqueous solution. Corrosive to metals and tissue. Noncombustible. Used in chemical manufacturing, petroleum refining, cleaning compounds.	[1] CAMEO Chemicals
–	Potassium hydroxide, [dry solid, flake, bead, or granular] appears as a white solid. Corrosive to metals and tissue. Used in soap manufacture, bleach, as an electrolyte in alkaline batteries, and as a food additive.	[1] CAMEO Chemicals
–	Liquid; Dry Powder; Liquid; Liquid; Other Solid; Dry Powder; Large Crystals; Large Crystals; CBI; Dry Powder; Other Solid	[2] EPA Chemical Data Reporting (CDR)
–	WHITE HYGROSCOPIC SOLID IN VARIOUS FORMS.	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	White, odorless solid or clear aqueous solution.	[4] Occupational Safety and Health Administration (OSHA)
–	Odorless, white or slightly yellow lumps, rods, flakes, sticks, or pellets. [Note: May be used as an aqueous solution.]	[5] The National Institute for Occupational Safety and Health (NIOSH)
–shown	White or colorless, orthorhombic, deliquescent pieces, lumps, or sticks having crystalline fracture	[6] Hazardous Substances Data Bank (HSDB)cites Lewis, R.J. Sr. (ed) Sax's Dangerous Properties of Industrial Materials. 12th Edition. Wiley-Interscience, Wiley & Sons, Inc. Hoboken, NJ. 2012., p. 3730

Value	As written	Source
360 °C	680 °F approximately (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
380 °Cshown	380 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
360 °C	680 °F	[4] Occupational Safety and Health Administration (OSHA)
406 °C	406 °C	[7] PAC Chemical Database, U.S. Department of Energy
380 °C	716 °F	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
1320 °C	2408 °F at 760 mmHg (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
1324 °Cshown	1324 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
1320 °C	2408 °F	[4] Occupational Safety and Health Administration (OSHA)
1327 °C	1327 °C @760 [mm Hg]	[7] PAC Chemical Database, U.S. Department of Energy
1324 °C	2415 °F	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
–	1.45 to 1.50 at 68 °F (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
–	2.04 at 59 °F (USCG, 1999) - Denser than water	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
–	1.188 at 29	[6] Hazardous Substances Data Bank (HSDB)cites Schultz H et al; Potassium Compounds. Ullmann's Encyclopedia of Industrial Chemistry. 7th ed. (1999-2015). New York, NY: John Wiley & Sons. Online Posting Date: a5 Jun 2000
–	1.514 at 50 /Aqueous potassium hydroxide/	[6] Hazardous Substances Data Bank (HSDB)cites Schultz H et al; Potassium Compounds. Ullmann's Encyclopedia of Industrial Chemistry. 7th ed. (1999-2015). New York, NY: John Wiley & Sons. Online Posting Date: a5 Jun 2000
–	2.04 g/cm³	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	2.04	[4] Occupational Safety and Health Administration (OSHA)
–shown	2.044 @25 °C	[7] PAC Chemical Database, U.S. Department of Energy
–	2.04	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
–	107 g/100 cc at 59 °F (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
–	Solubility in water (g KOH/100 g H2O): 97 at 0 °C; 103 at 10 °C; 112 at 20 °C; 126 at 30 °C; 178 at 100 °C	[6] Hazardous Substances Data Bank (HSDB)cites Schultz H et al; Potassium Compounds. Ullmann's Encyclopedia of Industrial Chemistry. 7th ed. (1999-2015). New York, NY: John Wiley & Sons. Online Posting Date: a5 Jun 2000
–	For more Solubility (Complete) data for POTASSIUM HYDROXIDE (6 total), please visit the HSDB record page.	[6] Hazardous Substances Data Bank (HSDB)
–shown	Solubility in water, g/100ml at 25 °C: 110 (very good)	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	(59 °F): 107%	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
1 mmHg	1 mmHg at 1326 °F	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
5 mmHg	5 mmHg at 1497 °F (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
1 mmHgshown	1 MM HG @ 714 °C	[6] Hazardous Substances Data Bank (HSDB)cites Sax, N.I. Dangerous Properties of Industrial Materials. 6th ed. New York, NY: Van Nostrand Reinhold, 1984., p. 1047
1 mmHg	1 mmHg at 1326 °F	[4] Occupational Safety and Health Administration (OSHA)
5 mmHg	5 mmHg at 1497 °F	[4] Occupational Safety and Health Administration (OSHA)

Each value as its source reports it, with the source's number after it (listed under References). Where several sources report a property, the row shows the value most of them agree on, the rule the app uses; open the values to see every one.

Calculated

Heavy atoms: 2
Rings: 0
Aromatic rings: 0
Fraction sp³ carbons (Fsp3): 0
H-bond donors: 0 computed here · PubChem 1
H-bond acceptors: 1
Rotatable bonds: 0
TPSA (Å²): 30 computed here · PubChem 1
Formal charge: 0
Complexity: 2 PubChem
Stereocenters: None
Double-bond geometry: None specified
Point group: C∞v of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

H1.80%
K69.69%
O28.52%

Isotope pattern

Each peak is a nominal mass with its abundance-weighted exact mass, as a percentage of the tallest, from IUPAC natural isotope abundances.

Computed from the structure with RDKit 2026.09 when this page was built, beside PubChem's own computed values from its record; where the two differ, both are shown.

Predicted

log P: -3.17 Crippen (Wildman and Crippen 1999)
log S (water solubility): 1.81 ESOL (Delaney 2004), log mol/L
Synthetic accessibility: 7.79 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

Molecular weight ≤ 500: 56.11
log P ≤ 5 (Crippen): -3.17
H-bond donors ≤ 5: 0
H-bond acceptors ≤ 10: 1

Passes all four rules.

Predictions, not measurements; each names its method. A measured log P, where a source reports one, is under Physical properties.

Safety

Danger

Harmonized EU classification (CLP Annex VI). Source [8].

Corrosive
Harmful or irritant

H302Harmful if swallowed
H314Causes severe skin burns and eye damage

Precautionary statements: P260, P264, P270, P280, P301+P317, P301+P330+P331, P302+P361+P354, P304+P340, P305+P354+P338, P316, P321, P330, P363, P405, P501

View all classifications (4)

[8] Regulation (EC) No 1272/2008 of the European Parliament and of the Council · DangerH302, H314
[9] European Chemicals Agency (ECHA)This chemical does not meet GHS hazard criteria for < 0.1% (3 of 4709) of reports.
[9] European Chemicals Agency (ECHA) · 4,709 reports · DangerH290, H302, H314, H318
[6] Hazardous Substances Data Bank (HSDB) · DangerH290, H302, H314, H318, H402

Exposure limits

PEL: None See Appendix G[5]
REL-C (Ceiling): 2 mg/m³[4]
REL: C 2 mg/m3[5]
TLV: 2 mg/m[3]
TLV-C (Ceiling): 2 mg/m³ [1992][4]
IDLH: N.D. See: IDLH index[5]

First aid

(Act quickly]) eyes: Flush with water for at least 15 min. Skin: Flush with water, then rinse with dilute vinegar (acetic acid). Ingestion: Give water and milk. Do NOT induce vomiting. Call physician at once, even when injury seems to be slight. (USCG, 1999)[1]
Eyes: First check the victim for contact lenses and remove if present. Flush victim's eyes with water or normal saline solution for 20 to 30 minutes while simultaneously calling a hospital or poison control center. Do not put any ointments, oils, or medication in the victim's eyes without specific instructions from a physician. Immediately transport the victim after flushing eyes to a hospital even if no symptoms (such as redness or irritation) develop. Skin: Immediately flood affected skin with water while removing and isolating all contaminated clothing.[1]
General First Aid: · Call 911 or emergency medical service. · Ensure that medical personnel are aware of the material(s) involved, take precautions to protect themselves and avoid contamination. · Move victim to fresh air if it can be done safely. · Administer oxygen if breathing is difficult. · If victim is not breathing: -- DO NOT perform mouth-to-mouth resuscitation; the victim may have ingested or inhaled the substance. -- If equipped and pulse detected, wash face and mouth, then give artificial respiration using a proper respiratory medical device (bag-valve mask, pocket mask equipped…[10]
General First Aid: · Call 911 or emergency medical service. · Ensure that medical personnel are aware of the material(s) involved, take precautions to protect themselves and avoid contamination. · Move victim to fresh air if it can be done safely. · Administer oxygen if breathing is difficult. · If victim is not breathing: -- DO NOT perform mouth-to-mouth resuscitation; the victim may have ingested or inhaled the substance. -- If equipped and pulse detected, wash face and mouth, then give artificial respiration using a proper respiratory medical device (bag-valve mask, pocket mask equipped…[10]

Storage

Separated from food and feedstuffs, strong acids and metals. Store only in original container. Dry. Well closed. Store in an area without drain or sewer access.[3]
Keep container tightly closed in a dry and well-ventilated place. Absorbs carbon dioxide (CO2) form air. Air sensitive. Strongly hygroscopic. Storage class (TRGS 510): Non-combustible, corrosive hazardous materials.[6]

Incompatibilities

Acids, water, metals (when wet), halogenated hydrocarbons, maleic anhydride [Note: Heat is generated if KOH comes in contact with water & carbon dioxide from the air].[6]
Above 84 °C it reacts with reducing sugars to form poisonous carbon monoxide gas. Violent, exothermic reaction with water. Potentially explosive reaction with bromoform + crown ethers, chlorine dioxide, nitrobenzene, nitromethane, nitrogen trichloride, peroxidized tetrahydrofuran, 2,4,6-trinitrotoluene. Reaction with ammonium hexachloroplatinate(2-) + heat forms a heat-sensitive explosive product.[6]
Molten ortho nitrophenol reacts violently with potassium hydroxide (commercial 85% pellets). When solid potassium hydroxide & tetrachloroethane are heated, a spontaneously flammable gas, chloroacetylene, is formed.[6]
/1,2-Dichloroethylene & potassium hydroxide reaction/ produces chloroacetylene, which is ... Spontaneously flammable in air.[6]

Safety data sheets on the supplier’s page: Thermo Fisher Scientific, LGC Standards, VladaChem.

Always read the supplier’s safety data sheet before working with it.

Literature

Reading PubChem, OpenAlex and GSRS…

Bioactivity

Reading ChEMBL…

References

[1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
[2]EPA Chemical Data Reporting (CDR) · Public domain (US EPA) · via PubChem · retrieved 2026-10-14
[3]ILO-WHO International Chemical Safety Cards (ICSCs) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
[4]Occupational Safety and Health Administration (OSHA) · Public domain (US DOL) · via PubChem · retrieved 2026-10-14
[5]The National Institute for Occupational Safety and Health (NIOSH) · Public domain (US CDC) · via PubChem · retrieved 2026-10-14
[6]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
[7]PAC Chemical Database, U.S. Department of Energy · Public domain (US DOE) · via PubChem · retrieved 2026-10-14
[8]Regulation (EC) No 1272/2008 of the European Parliament and of the Council · EU reuse policy, CC BY 4.0 · via PubChem · retrieved 2026-10-14
[9]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
[10]Emergency Response Guidebook (ERG) · Public domain (US DOT) · via PubChem · retrieved 2026-10-14
·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
·Literature on PubChem

Data last updated 2026-10-14.