Sodium Hydroxide
Properties
| State | Solid (white, deliquescent pellets or flakes) |
| Color | White |
| Solubility | Highly soluble in water (1110 g/L at 25 °C; dissolution is exothermic at -44.5 kJ/mol) |
| Melting Point | 323 °C |
| Boiling Point | 1388 °C |
About Sodium Hydroxide
Sodium hydroxide (NaOH, MW 39.997), the lye that has been called caustic soda since the Leblanc process days, is the strong base that essentially every chemistry workflow eventually leans on. Production runs above 80 million tonnes per year, almost entirely from the chlor-alkali electrolysis of saturated NaCl brine in membrane cells: 2NaCl + 2H2O -> 2NaOH + Cl2 + H2, where NaOH is the cathode product and Cl2 the co-product that drives PVC manufacture. The salt dissociates completely in water (pKb effectively negative) so 0.1 M NaOH gives pH 13 and 1 M gives 14. Dissolution is sharply exothermic at -44.5 kJ/mol, which is why pellets dropped into a beaker can boil the water if you go too fast. In the lab it's the standard titrant for acid-base work (carbonate-free 0.1 M against potassium hydrogen phthalate) and the saponification reagent that converts triglycerides into glycerol plus fatty acid soap. Industrially it digests bauxite in the Bayer process to extract aluminum, dissolves lignin from wood chips in the Kraft pulping process that makes brown paper, regenerates ion-exchange columns, and unblocks drains by saponifying grease and dissolving hair (proteinaceous keratin hydrolyzes in strong alkali). Bench-grade NaOH is intensely deliquescent and CO2-reactive, forming a hygroscopic Na2CO3 crust within minutes of air exposure, so it has to be stored in tightly sealed plastic and standardized fresh.
Where you'll encounter it
If you've ever made a soft pretzel (the lye dip is what gives the mahogany crust and that distinctive flavor), unclogged a kitchen sink with Drano, or developed black-and-white film, you've used NaOH. In an organic chemistry lab, 6 M NaOH is the standard wash to extract carboxylic acid impurities from an organic layer in a separatory funnel; the acid deprotonates and partitions into the aqueous phase as the sodium salt. In a biochemistry lab, the alkaline lysis miniprep starts with 0.2 M NaOH plus 1% SDS to denature E. coli genomic DNA and proteins while leaving plasmid DNA renaturable. In a chemistry teaching lab, the standard introductory titration is 0.1 M NaOH against 0.1 M HCl with phenolphthalein; the endpoint shift from colorless to pink at pH 8.3 is most students' first hands-on experience with strong-acid strong-base neutralization.
Common Uses
- Chlor-alkali co-product alongside Cl2 and H2 from membrane-cell electrolysis of brine
- Bayer process digestion of bauxite to extract Al(OH)3 in alumina refining
- Kraft process white liquor for pulping wood into brown paper and kraft cardboard
- Saponification reagent that converts triglycerides to soap and glycerol
- 0.1 M titrant standardized against KHP for acid-base titrations
- Drano-style drain cleaner that hydrolyzes hair and saponifies grease clogs
- Lye-bath dip for soft pretzels, bagels, and Bavarian breads (Maillard browning)
- Lysis buffer base for plasmid minipreps and SDS-PAGE sample preparation
Safety Information
Highly corrosive to skin, eyes, and mucous membranes. Solutions above 0.5 M cause liquefactive necrosis on contact, and splashes to the eye can scar the cornea within seconds; copious water irrigation for at least 15 minutes is the standard first aid. Airborne limits are written as ceilings rather than time-weighted averages, because the injury is immediate contact damage and not cumulative dose. GHS classifications: H290 (may be corrosive to metals), H314 (causes severe skin burns and serious eye damage), H318 (subset of H314 if reported separately). Pictogram: Corrosion (GHS05). Heat of dissolution is large enough to crack glassware and boil water; always add NaOH slowly to water (never the reverse) with stirring. Reacts violently with acids and with reactive metals (Al, Zn) liberating H2 gas. Standard PPE: chemical splash goggles, face shield for transfers, butyl or neoprene gloves (nitrile fails above 30%), lab coat, and a deluge shower within 10 seconds.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.