Lye is a basic component of soap making. It is extremely difficult, if not outright impossible, to make soaps without it. Lye is a corrosive alkaline chemical commonly leached from hardwood ashes. It is a highly reactive substance and is capable of dissolving viscid substances like fats. The term may refer to both sodium and potassium hydroxide; the former is used to make soap bars while the latter is used to make liquid soaps. This article will focus on sodium hydroxide.
Sodium hydroxide, or caustic soda, is commonly produced through the reaction of soda (sodium carbonate) and lime (calcium carbonate). It is usually available as flakes, grains, pellets, or in a saturated solution. Aside from soap making, it is an important industrial product for pulp and paper manufacturing, textile production, water purification, and drain cleaning.
Despite its corrosive nature, sodium hydroxide is also used in food preparation. Primarily used for vegetable washing and chemical peeling, it is also used in food processing and preservation. It is a curing agent for olives, century eggs, hominy, and lutefisk. Lye rolls and pretzels are coated with a sodium hydroxide solution to get their characteristic taste and color.
Properties:
- Chemical formula: NaOH
- Molar mass: 39.9971 g. mol-1
- Boiling point: 1390°C
- Melting point: 323°C
- Vapor pressure: 0.07 mmHg (300°C)
- Density: 2.13 g/cm3
- Viscosity: 4.0 cp (350°C)
- Surface tension: 74.35 g/s2 (18°C)
- Refractive index: 1.412 (420°C)
- Dielectric constant: 57.5 (25°C)
- Thermal expansion: 8.4E – 5/K (20°C)
- Heat of fusion: 8.4kJ/mol
- Heat of vaporization: 175 kJ/mol
Safety:
Sodium hydroxide is a highly caustic substance and should be handled carefully. In its solid or liquid form, it can cause chemical burns. Before handling the chemical, protective equipment like rubber gloves, goggles, and laboratory gown should be worn. Soap making should be done in a well-ventilated area to avoid inhaling its fumes. Always add sodium hydroxide to the solvent slowly, not the other way around.
Dissolved caustic soda is highly exothermic and may cause heat burns and ignite flammable substances, so it should be kept away from incompatible chemicals. Protect sodium hydroxide from water and moisture as it can cause violent reaction. Wash hands thoroughly after working with the chemical. When not in use, it should be stored in a cool, dry place.
Incompatibilities
Caustic soda should be kept away from acids and organic halogen compounds as contact with any of these may cause violent reaction. Exposure to nitromethane and similar compounds should also be avoided to prevent formation of shock-sensitive salts. Caution should be exercised when compound is exposed to metals like aluminum, magnesium, tin, and zinc, as it may cause hydrogen gas formation. Diluted sodium hydroxide readily reacts with various sugars as well and produces poisonous carbon monoxide fumes.
