| Synonyms | Caustic soda, Sodium Hydroxide, NaOH |
| Appearance | Colourless/white crystalline solid |
| Odor | Odorless |
| Molecular weight | 39.9971 |
| Molar mass | 39.9971 g/mol |
| Melting point | 323 °C |
| Boiling point | 1388 °C |
| Water solubility | 1000 g/L (25 °C), 3370 g/L (100 °C), Exothermic reaction |
| Solubility in Methanol | Soluble |
| Solubility in Ethanol | Soluble |
| Solubility in ether | Insoluble |
| Refractive index (nD) | 1.3576 |
| Remarks | Hygroscopic |
- Sodium hydroxide (NaOH), also known as caustic soda or lye, is a highly caustic and reactive inorganic base that appears as a white solid or as a clear, colorless solution when dissolved in water. It is one of the most widely used alkalis in both industrial and laboratory settings. Due to its strong basicity and ability to react vigorously with acids, fats, and proteins, sodium hydroxide plays essential roles in chemical synthesis, biochemistry, and biotechnology.
- In aqueous solutions, sodium hydroxide completely dissociates into sodium (Na⁺) and hydroxide (OH⁻) ions, raising the pH and creating a strongly alkaline environment. This property makes it indispensable for pH adjustments and for reactions requiring high alkalinity. NaOH is highly exothermic when dissolved in water, so proper handling and dilution protocols are important to avoid burns or splashes.
- One key laboratory application of sodium hydroxide is in the Biuret test for protein quantification, where it provides the alkaline environment necessary for copper ions to react with peptide bonds in proteins. Without the strong alkalinity provided by NaOH, the Biuret reaction cannot proceed effectively, making it a crucial component of the assay.
- Sodium hydroxide is also an essential reagent in molecular biology, especially in plasmid DNA isolation. During the alkaline lysis step of plasmid purification, a high-pH NaOH solution is used to denature chromosomal and plasmid DNA, as well as to disrupt the cell wall and membrane. Subsequent neutralization allows selective renaturation of plasmid DNA while precipitating genomic DNA and proteins, facilitating the separation and purification of plasmid DNA from bacterial cells.
- Beyond the laboratory, sodium hydroxide is widely used in soap and detergent production, paper manufacturing, water treatment, and chemical processing. In cleaning products, it serves as a powerful degreasing agent and drain cleaner due to its ability to saponify fats and dissolve organic matter. In the paper industry, NaOH is used in the Kraft process to break down lignin and extract cellulose from wood pulp.
- Despite its versatility, sodium hydroxide is a hazardous chemical that can cause severe chemical burns upon contact with skin or eyes and is corrosive to many materials. It must be handled with care, using appropriate personal protective equipment and proper storage procedures.
- In conclusion, sodium hydroxide is a fundamental chemical in both research and industry. Its strong alkaline properties make it vital for a range of biochemical assays (such as the Biuret test), nucleic acid extraction protocols (such as plasmid isolation), and a variety of industrial processes.
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