Sodium Hydroxide
CAS 1310-73-2 NaOH
- CAS number
- 1310-73-2
- EC number
- 215-185-5
- Formula
- NaOH
- Molar mass
- 40.00 g/mol
- Appearance
- One substance in two commercial forms. As a solid it is white, opaque and strongly hygroscopic, supplied as flakes, pearls or prills. As an aqueous solution it is a clear, colourless, slightly viscous liquid; at the 50% strength that carries most of the trade, density is around 1.52–1.53 g/mL at 20 °C and crystallisation begins near 12 °C.
- HS code
- 2815.11 (solid) · 2815.12 (aqueous solution)
Caustic soda is the workhorse alkali of industrial chemistry, and it is bought in two forms that are the same chemical. Solid flakes, pearls and prills carry no water, so freight pays only for alkali, but they have to be dissolved on site, which means dust handling and a strong exotherm to manage. Aqueous solution is pumped straight into the process instead, at the cost of shipping water. Most of the tonnage moves as the 50% solution, which is why its two properties are worth knowing up front: it is half water by weight, and it begins to crystallise near 12 °C, so tanks are insulated or heat-traced. Among solution grades the deciding number is usually leftover salt from the cell that made them — membrane grade below about 100 ppm sodium chloride, diaphragm grade around 1.1%. Ehlinar supplies solid and solution, in membrane, diaphragm and food grades including specified low heavy-metal material.
Applications
Grades & packaging
Supplied solid — flakes, pearls or prills, typically ≥98–99% — and as aqueous solution, most often at 50% but also at 32% and other strengths to order. Solution grades are named for the cell that produced them, and residual salt is what separates them: membrane grade carries under about 100 ppm sodium chloride against roughly 1.1% for diaphragm. Rayon (mercury-cell) grade, food grade meeting Food Chemicals Codex test requirements, and specified low heavy-metal grades are also traded. Specify form, strength and grade.
- Solid: 25 kg PE-lined bags, 500–1000 kg bulk bags, drums
- Solution: drums (~250–300 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) | ≥98–99% NaOH |
| Solution strengths | 50% most traded; 32% and others to order |
| Density at 20 °C (50% solution) | ~1.52–1.53 g/mL |
| Crystallisation onset (50% solution) | ~12 °C (54 °F) |
| Sodium chloride | <100 ppm membrane grade; ~1.1% diaphragm grade |
| Materials of construction | Carbon steel; lined steel, 304L/316L or PE where iron matters — never aluminium, zinc or tin |
Also known as
Caustic soda · Soda lye · Liquid caustic · Lye · Sodium hydrate · Caustic soda flakes / pearls / prills
Frequently asked questions
- What is the difference between membrane and diaphragm grade caustic soda?
- Mainly residual salt from the electrolytic cell that produced it. Membrane grade holds under about 100 ppm sodium chloride; diaphragm grade holds up to roughly 1.1%. Membrane material is also clearer and generally lower in other impurities, which is why it is specified where chloride would corrode equipment or spoil a product.
- Why does 50% caustic soda solidify in the tank?
- Because that concentration sits near a maximum in the freezing curve. The 50% solution begins to crystallise at about 12 °C (54 °F), and once crystals form they plug lines and pumps. Insulation, heat tracing or a heated store solves it; so does taking a weaker strength such as 32%, which freezes lower — one reason to specify strength rather than default to 50%.
- Should I buy solid or solution?
- It is a freight-against-handling decision. A 50% solution is half water, so long-distance carriage pays to move that water; solid flakes, pearls and prills do not. Against that, solution needs no dissolving step, generates no caustic dust and avoids the strong exotherm of making up a batch on site. Short haul and continuous use tend to favour the liquid, long haul and intermittent use the solid. Both are the same chemical, so the choice is logistics rather than specification.
- What should the storage tank be made of?
- Carbon steel is standard at ambient temperature and is what most bulk storage uses. Where iron pick-up would contaminate the product, use epoxy-lined carbon steel, 304L or 316L stainless, or polyethylene or polypropylene. Never aluminium, zinc or tin: caustic attacks all three and liberates hydrogen.
- Can I dilute it on site?
- Yes, and it is common practice, but the heat of dilution is substantial and can flash-boil a poorly made addition. Add the caustic to the water, never the reverse, with agitation and cooling, and control the addition rate.
- Is there a food-grade caustic soda?
- Yes — material that meets the test requirements of the Food Chemicals Codex, used in caustic peeling, olive curing and cocoa processing. Note that meeting FCC test requirements and being manufactured under cGMP are two separate things; confirm both against the supplier documentation if your application needs them.
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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.