| CAS number|| 1310-73-2|
| Molecular weight|| 40.0 amu|
| Melting point|| 596 K (323 °C)|
| Boiling point|| 1663 K (1390 °C)|
| Density|| 2.1 g/cm|
| Crystal structure|| ?|
| Solubility|| 111 g/100 g of water|
| Solution density|| table|
| Acid - Base properties|
| pKb|| 0.2 |
| ΔfH0gas|| -197.76 kJ/mol|
| ΔfH0liquid|| -416.88 kJ/mol|
| ΔfH0solid|| -425.93 kJ/mol|
| S0gas, 1 bar|| 228.47 J/mol·K|
| S0liquid, 1 bar|| 75.91 J/mol·K|
| S0solid|| 64.46 J/mol·K|
| Ingestion|| May cause severe and permanent damage to the gastrointestinal system.|
| Skin|| Dangerous. Symptoms range from mild irritation to severe ulcers.|
| Eyes|| Dangerous. May cause burns and damage to cornea or conjunctiva.|
|SI units and standard conditions used unless otherwise stated.|
), also known as caustic soda
, is a caustic metallic base
used in industry (mostly as a strong chemical base
) in the manufacture of paper
, textiles, and detergents.
Sodium hydroxide is occasionally used in the home as an agent for unblocking drains, but it is highly caustic and has a high danger of causing chemical burns, permanent injury or scarring, and blindness, due to its high reactivity. Therefore, it should be stored separately.
Sodium hydroxide is relatively stable and incompatible with many substances. It dissolves very easily in water, however the dissolution is highly exothermic
. For this reason, it is important to have the proper type of chemical fire extinguisher nearby before working with sodium hydroxide. Store NaOH in an airtight container to prevent it from absorbing water and CO2
from the air. It can create enough heat to ignite flammables (such as alcohols
), so add slowly in biodiesel processors
Sodium hydroxide is produced in the Chloralkali process
, which is the electrolysis
of an aqueous solution of sodium chloride
. It is a by-product from the production of chlorine
. A sodium hydroxide solution
will leave a yellow stain on fabric and paper.
Both sodium hydroxide (NaOH) and potassium hydroxide
(KOH) are commonly called "lye" in North America, which can lead to some confusion. However, most commercially available lye is NaOH. Lye is also a main ingredient in the making of soap. NaOH is now most commonly used for this, but traditionally KOH was used because it was easier to obtain.
, sodium hydroxide is used as a catalyst
. This only works with anhydrous
sodium hydroxide, because water and lye would turn biodiesel into soap (saponification
It is used more often than potassium hydroxide because it costs less, especially as a smaller quantity is needed for the same results. Another alternative is sodium silicate.
Vinegar is a mild acid that will neutralize lye if it were to make contact with the skin.
Food uses of lye include washing or chemical peeling of fruits and vegetables, chocolate and cocoa processing, caramel color production, poultry scalding, soft drink processing, and thickening ice cream. Olives are often soaked in lye to soften them, while pretzels and German
lye rolls are glazed with a lye solution before baking to make them crisp.
Lye is used to make the Scandinavian delicacy known as lutefisk (from lutfisk
, "lye fish"). Cod is soaked in lye to a jelly-like consistency, then served with bacon fat, potatoes, brunost sauce, and mushy peas.
Hominy is dried maize (corn) kernels reconstituted by soaking in lye-water.