- What it is. This sodium hydroxide is a 50% (w/v) aqueous solution, containing 50 g of NaOH per 100 mL, supplied in a 1-gallon size. It is a highly concentrated alkaline liquid for laboratory reagent preparation, digestion, and pH control.
- Concentration. Weight-per-volume strength means 500 g of sodium hydroxide in each liter of solution, about 12.5 M (calculated). Because it is defined per liter, it is easy to dose by volume, but it is not the same as 50% (w/w) caustic, which contains more NaOH per liter.
- 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.
- w/v versus w/w. Industrial 50% caustic soda is usually specified by weight (w/w). At a density of about 1.52 g/cm³, 50% (w/w) caustic contains about 760 g of NaOH per liter, roughly 19 M. Check the label before substituting one for the other.
- Laboratory uses. Use concentrated sodium hydroxide in Kjeldahl distillation to release ammonia from digested samples, in alkaline digestions, for quick pH adjustment of large volumes, and to prepare weaker standard bases by dilution.
- Exothermic dilution. Diluting concentrated caustic releases substantial heat. Add it slowly to cold water with stirring, ideally in an ice bath for large volumes, and never add water to the concentrate.
- 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 (w/v) sodium hydroxide is used for Kjeldahl distillations, alkaline digestions, preparing dilute bases, pH adjustment in reagent and waste treatment, equipment cleaning, and chemical synthesis.
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/v), 500 g/L |
| Approximate Molarity | About 12.5 M (calculated) |
| Appearance | Clear, colorless to slightly hazy liquid |
| Water Solubility | Miscible |
| Hazard Statements (typical NaOH solutions) | H290 (corrosive to metals), H314 (severe burns) |
| DOT (typical) | UN1824, Sodium hydroxide solution, Class 8 |
| Exposure Limit | NIOSH REL 2 mg/m³ ceiling |
| Package Size | 1 gallon |
Applications / Common Uses
- Kjeldahl distillation: Releases ammonia from digested samples.
- Alkaline digestion: Digests organic samples.
- Base preparation: Prepares dilute NaOH solutions.
- pH adjustment: Raises pH of large volumes quickly.
- Waste neutralization: Neutralizes acidic waste.
Storage, Handling & Shipping
Caution: Concentrated sodium hydroxide causes severe skin burns and eye damage and corrodes 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.
- 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 difference between 50% w/v and 50% w/w sodium hydroxide?
A 50% (w/v) solution contains 500 g of NaOH per liter, about 12.5 M. A 50% (w/w) solution contains 50 g per 100 g of solution, which, at a density near 1.52, equals about 760 g per liter, roughly 19 M. Always check which basis your method specifies.
Why is 50% sodium hydroxide used in Kjeldahl analysis?
After acid digestion converts organic nitrogen to ammonium sulfate, concentrated sodium hydroxide makes the digest strongly alkaline, releasing ammonia gas for distillation. Using a concentrated solution keeps the added volume small, which helps distillation and ensures complete ammonia release. Add it carefully down the side of the flask so it layers beneath the acid digest.
How do I dilute 50% sodium hydroxide safely?
Add the caustic slowly to cold water while stirring, using an ice bath for larger volumes, since dilution releases substantial heat. Wear goggles, a face shield, and alkali-resistant gloves, and never add water to the concentrate. Cool before final volume adjustment. Label the diluted solution.
Does 50% (w/v) sodium hydroxide freeze?
Concentrated sodium hydroxide solutions can crystallize at cool temperatures. Fifty-percent (w/w) caustic crystallizes near 12 °C; this weight-per-volume solution is somewhat more dilute but should still be stored at room temperature. Warm gently and mix if crystals appear. Confirm storage temperature on the safety data sheet.
What PPE is required for concentrated caustic?
Wear chemical splash goggles, a face shield, alkali-resistant gloves (e.g., neoprene or butyl), and a lab coat or apron. Work where an eyewash station and safety shower are available, and rinse any contact immediately for at least 15 minutes. Remove contaminated clothing promptly. Never work alone.
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