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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
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Kjeldahl distillation: Releases ammonia from digested samples.
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Alkaline digestion: Digests organic samples.
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Base preparation: Prepares dilute NaOH solutions.
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pH adjustment: Raises pH of large volumes quickly.
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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.
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Incompatible materials: Acids, aluminum, zinc, tin, and other reactive metals, and organic halogen compounds.
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Exposure limit (NaOH): NIOSH REL 2 mg/m³ ceiling.
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Spill response: Contain with inert absorbent, neutralize cautiously with a weak acid, and rinse with water.
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First aid: Skin or eyes: flush with water for at least 15 minutes and seek immediate medical attention.
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