- What it is. This sodium hydroxide is a standard 50% (w/w) caustic soda solution, available in 1-gallon and 30-gallon sizes. It is the most concentrated common form of liquid caustic, used for chemical processing, neutralization, cleaning, and preparing dilute bases.
- Concentration. Every 100 g of solution contains 50 g of sodium hydroxide. With a density of about 1.52 g/cm³, that equals roughly 760 g of NaOH per liter, about 19 M (calculated).
- Chemical identity. Sodium hydroxide (caustic soda, CAS 1310-73-2, NaOH, 40.00 g/mol) is a strong base that dissociates completely in water. It neutralizes acids, saponifies fats and oils, and dissolves aluminum, zinc, and many organic residues.
- Why buy a liquid concentrate. Dissolving solid sodium hydroxide releases a large amount of heat and creates caustic dust and spatter. A prepared solution removes that hazard, is easier to meter and pump, and gives consistent strength for dilution and dosing.
- Crystallizes when cold. Fifty-percent caustic soda melts near 12 °C, so it can crystallize in cool storage areas. Keep it in a heated or temperature-controlled space; if crystals form, warm gently and mix thoroughly before use, since crystals and liquid differ in concentration.
- Physical properties. Fifty-percent sodium hydroxide boils near 135-140 °C and has a low vapor pressure of about 2 hPa at 20 °C. It is viscous and much denser compared with water, which affects pumping and metering.
- Why 50% is the standard. Fifty percent is the concentration at which caustic soda is commonly produced and shipped, giving the highest alkalinity per volume in liquid form and reducing transport and storage volume compared with weaker solutions.
- Carbon dioxide uptake. Like all hydroxide solutions, sodium hydroxide absorbs carbon dioxide from the air, forming sodium carbonate and slowly lowering effective alkalinity. Keep containers sealed between uses.
- Handling at a glance. Concentrated sodium hydroxide causes severe burns that may not be immediately painful, and it is especially damaging to the eyes. Wear chemical splash goggles, a face shield, and alkali-resistant gloves, and keep an eyewash station and safety shower nearby.
- Where it is used. Fifty-percent caustic soda is used in chemical manufacturing, pulp and paper, textile processing, soap and detergent production, water treatment pH control, wastewater neutralization, clean-in-place systems, and as a concentrate for preparing dilute caustic solutions.
Technical Specifications
| Chemical Name | Sodium hydroxide, aqueous solution |
| CAS Numbers | 1310-73-2 (sodium hydroxide); 7732-18-5 (water) |
| EC Number (NaOH) | 215-185-5 |
| Synonyms | Caustic soda solution, lye solution, NaOH solution |
| Formula (active) | NaOH |
| Molecular Weight (active) | 40.00 g/mol |
| Concentration | 50% (w/w) |
| Density | About 1.52 g/cm³ (20 °C) |
| Approximate Molarity | About 19 M (calculated) |
| NaOH per Liter | About 760 g (calculated) |
| Boiling Point | About 135 to 140 °C |
| Melting / Crystallization Point | About 12 °C |
| Vapor Pressure | About 2 hPa (20 °C) |
| pH | 14 |
| Appearance | Clear, colorless liquid |
| Hazard Statements | H290 (corrosive to metals), H314 (severe burns) |
| DOT | UN1824, Sodium hydroxide solution, Class 8, PG II |
| Exposure Limit | NIOSH REL 2 mg/m³ ceiling |
| Package Sizes | 1 gallon; 30 gallon |
Available Variants
- ZS0609-128 (SH9150-38): 1 gallon for laboratories and pilot plants.
- ZS0609-30 (SH9150-30): 30 gallon for production and process use.
Applications / Common Uses
- Chemical manufacturing: Supplies alkalinity for reactions and neutralization.
- Water treatment: Controls pH in drinking and process water.
- Wastewater neutralization: Raises pH of acidic effluent.
- Soap and detergent production: Saponifies fats and oils.
- Dilute caustic preparation: Serves as a concentrate for working solutions.
Storage, Handling & Shipping
Caution: Concentrated sodium hydroxide causes severe skin burns and eye damage and is corrosive to aluminum and zinc. Wear chemical splash goggles, a face shield, and alkali-resistant gloves, and always add base slowly to water when diluting.
Store tightly closed in a corrosives area for bases, separated from acids, reactive metals such as aluminum and zinc, and organic halogen compounds. Use secondary containment and keep containers sealed to limit carbon dioxide uptake. Store above about 15 °C to prevent crystallization, and use alkali-rated pumps for transfers from larger sizes.
- Incompatible materials: Acids, aluminum, zinc, tin, and other reactive metals, and organic halogen compounds.
- Exposure limit (NaOH): NIOSH REL 2 mg/m³ ceiling.
- Spill response: Contain with inert absorbent, neutralize cautiously with a weak acid, and rinse with water.
- First aid: Skin or eyes: flush with water for at least 15 minutes and seek immediate medical attention.
Related Categories & Services
- Shop Bases for related products in this category.
- Explore Inorganic Chemicals and ACS Grade Laboratory Chemicals.
- Vendor Managed Inventory (VMI) Program: Lab Pro can stock, track, and replenish this item on site so it never runs out. Contact info@labproinc.com or 888-452-2776 to set up a VMI assessment.
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FAQs
What is the molarity of 50% sodium hydroxide?
At 50% by weight and a density of about 1.52 g/cm³, the solution contains roughly 760 g of sodium hydroxide per liter, which is about 19 M. Lot assay and density vary slightly, so use certificate values when your calculations require exact concentration. Check the lot certificate.
Why does 50% caustic soda crystallize?
50% sodium hydroxide has a melting point near 12 °C, so it can crystallize in cool rooms or during winter shipping. Store it above about 15 °C. If crystals form, warm the container gently and mix thoroughly before use, since crystals change the liquid's concentration.
How do I dilute 50% sodium hydroxide?
Add the caustic slowly to cold water while stirring, never water to caustic, because dilution releases substantial heat. Use an ice bath for larger volumes; wear goggles, a face shield, and alkali-resistant gloves; and cool the solution before adjusting the final volume. Label the diluted solution.
Which size should I choose?
Choose 1 gallon for laboratories, pilot plants, and occasional use. Choose 30 gallons for production processes, water treatment, and continuous dosing. Larger sizes need secondary containment, temperature-controlled storage, and alkali-rated pumps for safe dispensing. Both sizes contain the same 50% (w/w) caustic soda, so performance and dilution calculations are identical.
What materials are compatible with 50% sodium hydroxide?
Carbon steel, stainless steel, polyethylene, and polypropylene are commonly used with caustic soda at ambient temperature. Avoid aluminum, zinc, galvanized steel, tin, and brass, which caustic attacks, releasing hydrogen. Check compatibility at elevated temperatures, where corrosion increases. Ask the equipment supplier if unsure, especially for seals and gaskets.
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