Potassium Hydroxide
CAS 1310-58-3 KOH
- CAS number
- 1310-58-3
- EC number
- 215-181-3
- Formula
- KOH
- Molar mass
- 56.11 g/mol
- Appearance
- One substance in two commercial forms. As a solid it is a white, very hygroscopic and deliquescent flake or pellet. As an aqueous solution it is a clear, colourless, strongly alkaline liquid; the 45% strength has a density around 1.45–1.46 g/mL at 20 °C.
- HS code
- 2815.20
Caustic potash is the potassium counterpart of caustic soda, and where a process needs the alkali without leaving sodium behind, it is the one that gets specified. Agriculture is the clearest case: potassium is a crop nutrient and sodium is not, so potassium hydroxide is the route into liquid fertilizers and potassium salts. Soap is the other classic case, since potassium soaps are the soft and liquid ones while sodium soaps set hard. It also serves as the electrolyte in alkaline batteries and in the alkaline electrolysers now being built for hydrogen. It is bought both as solid flake or pellet and as solution; of the two standard solution strengths, 45% is the one most often handled at ambient temperature, because 50% begins to crystallise near 4 °C. Ehlinar supplies solid and solution, in technical, food and specified low-iron grades.
Applications
Grades & packaging
Supplied solid as flake or pellet, typically 90% or ≥95%, and as membrane-cell aqueous solution at the two standard strengths, 45% and 50%. Technical, food grade meeting Food Chemicals Codex test requirements, and specified low-iron or low-chloride grades are traded; potassium chloride typically sits below 60 ppm in 45% caustic potash. Specify form, strength and grade.
- Solid: 25 kg PE-lined bags or drums, 500–1000 kg bulk bags
- Solution: drums (~250–275 kg net), IBC
- ISO tanks and road tankers
- Bulk
How we supply
- Certificate of Analysis (CoA), lot-specific where available
- Safety Data Sheet (SDS / MSDS)
- Technical Data Sheet (TDS)
- Certificate of Origin / Certificate of Conformity
Independent third-party inspection can be arranged on request, with the agency and scope agreed per trade. Representative samples can be requested for qualification, subject to supplier availability. We recommend incoming quality control against the agreed CoA.
Quoted on standard Incoterms (e.g. EXW, FOB, CIF, DAP) as agreed per trade. Delivery region, packaging and grade are confirmed per quote.
Documents and services above are subject to supplier availability and confirmed per quote; nothing here is an offer.
Typical / indicative values — not a binding specification
| Property | Typical |
|---|---|
| Assay (solid) | 90% or ≥95% KOH, flake or pellet |
| Solution strengths | 45% and 50% are the standards |
| Density at 20 °C (45% solution) | ~1.45–1.46 g/mL |
| Potassium chloride | Typically <60 ppm at 45% |
| Crystallisation onset | ~4 °C (40 °F) at 50%; lower at 45% |
| Materials of construction | Carbon steel at 27–38 °C; lined steel, 304L/316L or PE where iron matters |
Also known as
Caustic potash · Liquid caustic potash · Potassium hydrate · Potash lye · Caustic potash flakes / pellets
Frequently asked questions
- Why is caustic potash usually sold at 45% rather than 50%?
- Handling temperature. The 50% solution begins to crystallise at about 4 °C (40 °F), which makes it awkward through a cold winter without heated storage. The 45% strength stays liquid across a wider ambient range. Both are standard commercial concentrations and both are produced by the membrane process.
- When should I use caustic potash instead of caustic soda?
- When the counter-ion matters. If the process leaves potassium in the product and potassium is wanted — fertilizer, liquid soap, a potassium salt — caustic potash is the right alkali. If the cation is irrelevant and cost dominates, caustic soda is normally cheaper per unit of alkalinity. Solubility of the resulting salts can also decide it.
- Can I substitute one for the other weight for weight?
- No. Potassium hydroxide has a molar mass of 56.11 against 40.00 for sodium hydroxide, so it takes about 1.4 times the mass to deliver the same alkalinity. The product salt is different too, which may or may not be acceptable downstream.
- Why does caustic potash make soft soap?
- Saponification is the same reaction either way, but the salt it produces is not. Potassium soaps are more soluble and stay soft or liquid; sodium soaps crystallise and set into a hard bar. That is the whole difference between a bar of soap and a liquid one, and it is why traditional soft soap was made from wood-ash potash.
- What should the storage tank be made of?
- Carbon steel at moderate temperature is standard, ideally around 27–38 °C. Where iron contamination is unacceptable, use epoxy-lined steel, 304L or 316L stainless, or polyethylene or polypropylene. If you use PVC or CPVC, check the cement: the silica filler in most of these glues is attacked by caustic potash and the joints eventually leak.
- Is it used in hydrogen electrolysers?
- Yes. Aqueous potassium hydroxide is the conducting electrolyte in alkaline water electrolysis, the longest-established route to electrolytic hydrogen, and in alkaline primary and rechargeable batteries. Those applications usually call for a low-iron, low-chloride grade.
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Figures and identifiers here are compiled from public references and provided for general information; they are indicative, not a specification. See all products.