Substance profile
Potassium hydroxide
Potassium hydroxide is white or colorless, orthorhombic, deliquescent pieces, lumps and is odorless.
01 · Identification
What Potassium hydroxide is
Potassium hydroxide is white or colorless, orthorhombic, deliquescent pieces, lumps and is odorless. Its molecular formula is HKO and its molecular weight is 56.106 g/mol. It boils at 1327 °C, melts at 406 °C.
Under the GHS it carries the signal word Danger. It is classed as corrosives.
02 · Identifiers
Potassium hydroxide identifiers and molecular data
Potassium hydroxide CAS number and EC number
Potassium hydroxide molecular formula and molecular weight
Other names for Potassium hydroxide
- caustic potash
- KOH
- Battery
- Lye
- Potassa
- Potassium Hydrate
- Potassium Hydroxide (Lye)
- Potassium Hydroxide, Solid
03 · GHS classification
Potassium hydroxide hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Potassium hydroxide pictograms and signal word
Potassium hydroxide hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| Acute toxicity - oral GHS chapter 3.1 | Category 4 | H302 | GHS07 |
| Skin corrosion/irritation GHS chapter 3.2 | Category 1A or 1B or 1C | H314 | GHS05 |
Where two values are shown with “or”, the hazard statement is shared by more than one category or by more than one class, and the code alone does not say which. H272, for example, belongs to oxidising liquids and to oxidising solids — the physical state decides. The binding answer for a specific entry is in the CLP Annex VI table itself.
Potassium hydroxide hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H302 | Harmful if swallowed. |
| H314 | Causes severe skin burns and eye damage. |
This page lists only the codes assigned to Potassium hydroxide. The full reference lives on the hazard statements hub, the precautionary statements hub and the GHS pictograms hub.
Safety Data Sheet
Getting an SDS for Potassium hydroxide
Our own Potassium hydroxide safety data sheet walks through all sixteen sections of the published data. What it is not is the document an inspector asks for: an SDS is issued for a product by its supplier, so the sheet covering the grade actually standing in your store exists only in that supplier’s version. Collecting those and keeping them current as suppliers revise them is a separate job.
04 · Precautionary statements
Potassium hydroxide precautionary statements
CLP Annex VI assigns 8 precautionary statements to Potassium hydroxide. They are grouped the way a label groups them: what to do before handling, what to do when something has already happened, how to store it and how to dispose of it.
Prevention
What to do before and during handling so the hazard never happens.
Response
What to do once exposure, spillage or fire has already happened.
Reading the notation. … is a blank the supplier fills in — not a truncated sentence.· [square brackets] mark a part printed only when it applies.
05 · Names in the regulation
Potassium hydroxide name in 23 EU languages
CLP Annex VI Part 3 is published in every language edition of the regulation, and the identification column is written out in each of them. Nothing below is translated by us: each line is the name as that edition prints it. Under Art. 18(2) the substance name from Annex VI is a lawful product identifier, so this is the wording to put on a label going to that market — and where the cell lists several designations, any one of them qualifies.
| Language | Name in CLP Annex VI Part 3 |
|---|---|
| Bulgarian български | калиев хидроксид калиева основа |
| Spanish español | Hidróxido de potasio potasa cáustica |
| Czech čeština | hydroxid draselný |
| Danish dansk | kaliumhydroxid kaustisk potaske |
| German Deutsch | Kaliumhydroxid ÄtzkaliKalilauge |
| Estonian eesti | kaaliumhüdroksiid kaustiline potas |
| Greek ελληνικά | υδροξείδιο του καλίου καυστική ποτάσσα |
| English English | potassium hydroxide caustic potash |
| French français | hydroxyde de potassium potasse caustique |
| Croatian hrvatski | kalijev hidroksid kaustična potaša |
| Italian italiano | idrossido di potassio potassa caustica |
| Latvian latviešu | kālija hidroksīds kaustiskais potašs |
| Lithuanian lietuvių | kalio hidroksidas kalio šarmas |
| Hungarian magyar | kálium-hidroxid marókáli |
| Maltese Malti | idrossidu tal-potassju potassju kawstiku |
| Dutch Nederlands | kaliumhydroxide bijtende potas |
| Polish polski | wodorotlenek potasu potaż żrący |
| Portuguese português | hidróxido de potássio potassa cáustica |
| Romanian română | hidroxid de potasiu potasă caustică |
| Slovak slovenčina | hydroxid draselný lúh draselný |
| Slovenian slovenščina | kalijev hidroksid kavstična pepelika |
| Finnish suomi | kaliumhydroksidi kalilipeä |
| Swedish svenska | kaliumhydroxid kalilut |
All 23 language editions of Annex VI carry this entry. Irish is the twenty-fourth official EU language and has no line here for a different reason: no consolidated CLP text has ever been published in Irish, so there is no Irish edition of Annex VI to quote a name from. Source: consolidated CLP, CELEX 02008R1272, language editions. © European Union, https://eur-lex.europa.eu — only the electronic Official Journal of the European Union is authentic.
06 · Label elements
Potassium hydroxide GHS label elements
Everything CLP Annex VI fixes for Potassium hydroxide, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Potassium hydroxide
- Harmful if swallowed.
- Causes severe skin burns and eye damage.
- Do not breathe dust/fume/gas/mist/vapours/spray.
- Do not eat, drink or smoke when using this product.
- Wear protective gloves/protective clothing/eye protection/face protection/hearing protection/…
- IF SWALLOWED:
- Immediately call a POISON CENTER/doctor/…
- Call a POISON CENTER/doctor/… if you feel unwell.
- Rinse mouth.
- Do NOT induce vomiting.
Supplier name, address and telephone number· Product identifier·Nominal quantity
Need this as an actual label? Open Potassium hydroxide in the GHS label constructor →
07 · Health hazards
Potassium hydroxide health hazards and exposure limits
Potassium hydroxide hazard summary
Liquid causes second or third degree burns after short contact. [CHRIS] Potassium hydroxide 30-70% is highly corrosive to skin; [Quick CPC] A corrosive substance that can cause pulmonary edema; [ICSC] See Sodium hydroxicde.
Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
Potassium hydroxide occupational exposure limits
| Limit | Value | Source |
|---|---|---|
| PEL | none See Appendix G | The National Institute for Occupational Safety and Health (NIOSH) |
| REL | 2 mg/m³ | Occupational Safety and Health Administration (OSHA) |
| REL | C 2 mg/m3 | The National Institute for Occupational Safety and Health (NIOSH) |
| IDLH | N.D. | The National Institute for Occupational Safety and Health (NIOSH) |
These are United States values. The European Union sets its own indicative and binding limits, and the figure that applies at a given workplace is the one in the local regulation — not the one shown here.
08 · Physical and chemical properties
Potassium hydroxide properties
Every value is shown with the conditions it was measured under and the source it came from. Where sources disagree, all values are listed rather than one being picked — the difference is usually a different form of the substance, not an error.
Potassium hydroxide boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 1327 °C (2420.6 °F) | HSDB | |
| 1324 °C (2415 °F) | NIOSH | ||
| 1320 °C (2408 °F) | at 760 mmHg | CAMEO |
Potassium hydroxide melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | 406 °C (762.8 °F) | HSDB | |
| 380 °C (716 °F) | NIOSH | ||
| 360 °C (680 °F) | CAMEO |
Potassium hydroxide density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 2.044 g/cm³ | HSDB | |
| 2.04 g/cm³ | NIOSH |
Potassium hydroxide solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | Soluble in 0.9 part water, about 0.6 part boiling water | HSDB | |
| Soluble in ethanol, methanol | HSDB | ||
| Solubility in water, 121 g/100 g water at 25 °C | at 25 °C | HSDB |
Potassium hydroxide vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 1 mmHg | at 714 °C | HSDB |
| 1 mmHg | at 713.89 °C | NIOSH | |
| 1 mmHg | at 718.89 °C | CAMEO |
Potassium hydroxide autoignition temperature
| Property | Value | Conditions | Source |
|---|---|---|---|
| Autoignition temperature | Not flammable (USCG, 1999) | CAMEO |
Potassium hydroxide lower explosive limit (LEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Lower explosive limit (LEL) | Noncombustible Solid; however, may react with H2O & other substances | NIOSH | |
| and generate sufficient heat to ignite combustible materials. | NIOSH |
Potassium hydroxide corrosivity
| Property | Value | Conditions | Source |
|---|---|---|---|
| Corrosivity | Corrosive | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Potassium hydroxide fire and explosion behaviour
These are descriptions rather than measured values, so they are kept out of the table above and quoted here with the source that reported them.
Potassium hydroxide fire potential
When wet, attacks metals such as aluminum, tin, lead & zinc to produce flammable hydrogen gas.
Source: Hazardous Substances Data Bank (HSDB)
10 · Handling and storage
Potassium hydroxide storage and handling
Potassium hydroxide reactive group
CAMEO Chemicals places Potassium hydroxide in the reactive group Bases, Strong. Compatibility with other chemicals is worked out from the group, not from the individual substance — which is why two substances you have never seen react can still be flagged as a pair that must be separated.
A reactive group is a CAMEO Chemicals (US NOAA) grouping, not a GHS hazard class: it has no code, no category and no legal force. It is what the storage compatibility matrix on this site computes from.
Potassium hydroxide safe 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.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Potassium hydroxide storage conditions
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.
Source: Hazardous Substances Data Bank (HSDB)
Potassium hydroxide incompatible materials
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].
Source: Hazardous Substances Data Bank (HSDB)
Potassium hydroxide reactivity
POTASSIUM HYDROXIDE, SOLUTION is a strong base dissolved in water. Reacts exothermically with all acids. Slowly dissolves glass. Attacks aluminum and zinc to generate flammable hydrogen gas. Ignited a polyethylene container liner when mixed with potassium persulfate by release of heat and oxygen [MCA Case History 1155. 1955].
Source: CAMEO Chemicals
Planning storage for a mix of chemicals? Check Potassium hydroxide in the storage compatibility matrix →
11 · Transport
Potassium hydroxide UN number and transport classification
Transport classification is a separate system from the GHS classification above. It decides how a package is marked and how a load may be carried; it does not follow from the workplace label, and the workplace label does not follow from it. The entries below are linked by CAS number, never by name.
The same CAS number is shipped under more than one UN number. Which entry applies follows from the form and the concentration of the consignment — read the proper shipping name, not the CAS.
Potassium hydroxide under UN 1813 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| POTASSIUM HYDROXIDE, SOLID | 8 | C6 | II | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 8 is “Corrosive substances” (ADR 2.1.1.1).
United States · 49 CFR 172.101 Hazardous Materials Table
| Proper shipping name (column 2) | Class or division | PG | Labels (column 6) |
|---|---|---|---|
| Potassium hydroxide, solid | 8 | II | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 8 is “Corrosive material” (49 CFR 173.2).
Potassium hydroxide under UN 1814 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| POTASSIUM HYDROXIDE SOLUTION | 8 | C5 | II | |
| POTASSIUM HYDROXIDE SOLUTION | 8 | C5 | III | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 8 is “Corrosive substances” (ADR 2.1.1.1).
United States · 49 CFR 172.101 Hazardous Materials Table
| Proper shipping name (column 2) | Class or division | PG | Labels (column 6) |
|---|---|---|---|
| Potassium hydroxide, solution | 8 | II | |
| Potassium hydroxide, solution | 8 | III | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 8 is “Corrosive material” (49 CFR 173.2).
12 · Questions
Potassium hydroxide — frequently asked questions
What is the CAS number of Potassium hydroxide?
The CAS number of Potassium hydroxide is 1310-58-3. Its EC number is 215-181-3.
What is the chemical formula of Potassium hydroxide?
The molecular formula of Potassium hydroxide is HKO and its molecular weight is 56.106 g/mol.
What does a Potassium hydroxide label have to show?
Under CLP Annex VI the label for Potassium hydroxide carries the pictograms Corrosion and Exclamation mark and the signal word is Danger.
Is Potassium hydroxide flammable?
CLP Annex VI assigns Potassium hydroxide no flammability hazard class. That is not a statement that it cannot burn: the harmonised list only records the hazards that were assessed for it.
Is Potassium hydroxide a carcinogen?
CLP Annex VI records no harmonised carcinogenicity classification for Potassium hydroxide. Annex VI is a list of agreed classifications, not a list of substances found safe, so this is an absence of a classification rather than a clean bill of health.
What is the exposure limit for Potassium hydroxide?
The US occupational exposure limit reported for Potassium hydroxide is none See Appendix G (The National Institute for Occupational Safety and Health (NIOSH)). Limits differ by country: the EU sets its own indicative and binding values, and the figure that applies at a given workplace is the one in the local regulation.
What is the boiling point of Potassium hydroxide?
The boiling point reported for Potassium hydroxide is 1327 °C (2420.6 °F) (HSDB).
What is the melting point of Potassium hydroxide?
The melting point reported for Potassium hydroxide is 406 °C (762.8 °F) (HSDB).
How should Potassium hydroxide be stored?
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. (Hazardous Substances Data Bank (HSDB))
Nearby
Substances next to Potassium hydroxide
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