Buy 50% caustic soda solution when you need to pump, meter, or dose sodium hydroxide continuously. Buy dry pellets, beads, or flake when you need long shelf storage, lower freight per pound of NaOH, or small-batch laboratory work. Both forms are the same chemical, CAS 1310-73-2. The decision is about handling, freight, and dilution heat — not purity.
What is the difference between 50% caustic soda and dry caustic soda?
Caustic soda is sodium hydroxide, CAS number 1310-73-2, molecular formula NaOH, molecular weight 40.0 g/mol. It is sold in two commercial families:
- Liquid caustic soda — sodium hydroxide dissolved in water and shipped at a fixed strength, most commonly 50% NaOH by weight. It arrives ready to pump.
- Dry caustic soda — the same compound in solid form, supplied as pellets, beads (prills), flake, or granular material. It must be dissolved before use in most wet processes.
The chemistry is identical once the solid is dissolved. What changes is how the material moves through your plant, what it costs to freight, and what safety controls you need at the point of use. For general background on the compound itself, see our guide to sodium hydroxide properties, uses, and safety.
How do the hard specifications compare?
| Property | 50% caustic soda solution | Dry caustic soda (pellets, beads, flake) |
|---|---|---|
| CAS number | 1310-73-2 | 1310-73-2 |
| Formula | NaOH in water | NaOH |
| Molecular weight | 40.0 g/mol (NaOH) | 40.0 g/mol |
| NaOH content | 50% by weight | Sold on assay — confirm on the lot COA |
| Density / specific gravity | 1.5 at 68 °F (about 12.5 lb per gallon) | 2.13 at 68 °F |
| Physical description | Colorless liquid | Colorless to white, odorless solid |
| Melting point | Not applicable (solution) | 605 °F |
| Boiling point | Not applicable (solution) | 2,534 °F |
| DOT identification | UN1824, ERG Guide 154 | UN1823, ERG Guide 154 |
| OSHA PEL | 2 mg/m³ TWA | 2 mg/m³ TWA |
| NIOSH REL | Ceiling 2 mg/m³ | Ceiling 2 mg/m³ |
| NIOSH IDLH | 10 mg/m³ | 10 mg/m³ |
| Flammability | Noncombustible | Noncombustible solid |
Physical and exposure values above are from the NIOSH Pocket Guide to Chemical Hazards entry for sodium hydroxide and PubChem CID 14798. Always confirm the values for your specific lot against the supplied Safety Data Sheet.
When should you buy 50% caustic soda solution?
Choose the 50% solution when any of the following apply:
- You dose continuously. Neutralization, pH control, CIP loops, and scrubber makeup all favor a liquid that a metering pump can handle without a dissolving step.
- You do not want a dissolving station. Dissolving dry caustic releases significant heat and requires an agitated, corrosion-resistant vessel plus operator training. A 50% solution removes that unit operation entirely.
- Your volume justifies bulk or tote delivery. Above roughly a tote per month, liquid handling is usually simpler than repeatedly opening and dissolving solid packages.
- Dust exposure is a concern. Solid caustic generates dust during transfer, and the OSHA PEL of 2 mg/m³ applies to that airborne particulate.
The trade-off: you are paying freight on roughly half a load of water, and the solution crystallizes at temperatures that occur in ordinary winter conditions, so tanks and lines are normally insulated or heat-traced. Ask your supplier for the crystallization curve for the exact strength you are buying.
When should you buy dry caustic soda pellets, beads, or flake?
- Freight efficiency matters. Dry caustic ships without the water, so the delivered cost per pound of contained NaOH is usually lower on long hauls.
- You use it intermittently. Sealed solid packages store well and do not need heated storage, which suits seasonal or low-frequency use.
- You need small, precise charges. Laboratories, pilot plants, and batch operations weigh out pellets far more conveniently than they meter a corrosive liquid.
- You need a strength other than 50%. Starting from solid gives you full control of the final concentration.
The trade-off: dissolving is exothermic and must be done deliberately, and solid handling introduces dust control and PPE requirements at every transfer point.
Does the form change the purity or grade you get?
No. Form and grade are separate specifications. You choose the physical form based on handling, then choose the grade based on the purity your application demands. RightPath supplies sodium hydroxide 50% solution in Standard/Production, ACS, USP, HPLC, and High Purity grades, matched to the application — large-scale manufacturing through analytical laboratory work. If you are unsure which grade designation your process actually requires, our explainer on ACS vs HPLC vs reagent grade covers how these standards differ.
Strength is quoted as percent NaOH by weight. Some legacy specifications express strength in degrees Baumé instead. If your spec uses Baumé, confirm the basis in writing and check the assay on the Certificate of Analysis rather than converting from memory.
How do you handle each form safely?
Both forms are corrosive to skin, eyes, and the respiratory tract, and both are corrosive to metals. NIOSH lists the incompatibilities as water, acids, flammable liquids, organic halogens, and metals including aluminum, tin, and zinc.
- Dilution is exothermic. NIOSH notes that sodium hydroxide in contact with water may generate enough heat to ignite combustible materials. Always add caustic to water, never water to caustic, and control the addition rate.
- Prevent skin and eye contact. NIOSH specifies eyewash and quick-drench facilities, removal of wet or contaminated clothing, and immediate flushing on contact.
- Do not use aluminum, tin, zinc, or galvanized equipment. These react with caustic and can generate hydrogen.
- Ship it correctly. Solid is UN1823 and solution is UN1824, and both fall under ERG Guide 154. See our overview of DOT hazmat classes, UN numbers, and packing groups.
What caustic soda does RightPath Industries stock?
RightPath Industries is a Pittsburgh-headquartered bulk chemical distributor supplying more than 8,000 chemicals, and a top-10 U.S. ethanol distributor. For sodium hydroxide we carry:
- Sodium Hydroxide, 50% Solution — ready-to-use liquid caustic for neutralization, cleaning, and processing, with lot control, in Standard/Production, ACS, USP, HPLC, and High Purity grades.
- Sodium Hydroxide Pellets — dry caustic for batch dissolving, laboratory use, and applications where you set the final concentration.
Both sit in our General Chemicals and Powdered Chemicals & Salts ranges. Current Safety Data Sheets are in our SDS library, and unit conversions are on our chemical tools and calculators page.
How do you order caustic soda from RightPath?
Tell us three things and we can quote same day: the form and strength you want (50% solution or pellets), the grade your process requires, and your annual or monthly volume with delivery location. We will come back with an all-in delivered price. Request bulk pricing. If you are still comparing suppliers, our bulk caustic soda supplier guide walks through what to ask.
Frequently asked questions
Is 50% caustic soda the same chemical as caustic soda flake?
Yes. Both are sodium hydroxide, CAS 1310-73-2. The 50% solution is sodium hydroxide already dissolved in water at 50% by weight, and flake, pellets, and beads are the same compound in solid form. Once the solid is dissolved to 50%, the two are chemically equivalent.
How much does a gallon of 50% caustic soda weigh?
About 12.5 pounds per US gallon. Sodium hydroxide solution has a density of 1.5 at 68 °F, and water weighs 8.345 pounds per gallon, so 1.5 × 8.345 is approximately 12.5 lb/gal. Use our conversion calculators to check volumes against a specific lot density.
What DOT hazard class is caustic soda?
Caustic soda ships as a corrosive material. Solid sodium hydroxide is UN1823 and sodium hydroxide solution is UN1824, and both are assigned ERG Guide 154. Confirm the packing group on your shipping papers, since it depends on concentration and packaging.
Can you dilute 50% caustic soda on site?
Yes, and it is common practice for producing 25%, 20%, or lower strengths. Dilution releases substantial heat, so add the caustic to water, never water to caustic, control the addition rate, and use a vessel rated for the temperature rise. NIOSH warns that sodium hydroxide contacting water can generate enough heat to ignite nearby combustible materials.
Which form is cheaper overall?
It depends on distance and volume. Dry caustic has a lower freight cost per pound of contained NaOH because you are not shipping water, but it adds a dissolving step, equipment, and labor at your site. The 50% solution costs more to freight but eliminates that unit operation. Compare delivered cost per pound of NaOH plus your in-plant handling cost, not the unit price alone.