The "sodium hydroxide" of commerce is often the monohydrate (density 1.829 g/cm3). Physical data in technical literature may refer to this form, rather than the anhydrous compound.
In general, such neutralization reactions are represented by one simple net ionic equation:
A few transition metals, however, may react vigorously with sodium hydroxide under milder conditions.
Unlike sodium hydroxide, which is soluble, the hydroxides of most transition metals are insoluble, and therefore sodium hydroxide can be used to precipitate transition metal hydroxides. The following colours are observed:
Sodium hydroxide is also produced by combining pure sodium metal with water. The byproducts are hydrogen gas and heat, often resulting in a flame.
This reaction is commonly used for demonstrating the reactivity of alkali metals in academic environments; however, it is not commercially viable, as the isolation of sodium metal is typically performed by reduction or electrolysis of sodium compounds including sodium hydroxide.
Sodium hydroxide is used in many scenarios where it is desirable to increase the alkalinity of a mixture, or to neutralize acids.
Another use is in Salt spray testing where pH needs to be regulated. Sodium hydroxide is used with hydrochloric acid to balance pH. The resultant salt, NaCl, is the corrosive agent used in the standard neutral pH salt spray test.
A solution of sodium hydroxide in water was traditionally used as the most common paint stripper on wooden objects. Its use has become less common, because it can damage the wood surface, raising the grain and staining the colour.
Sodium hydroxide is used in some cement mix plasticisers. This helps homogenise cement mixes, preventing segregation of sands and cement, decreases the amount of water required in a mix and increases workability of the cement product, be it mortar, render or concrete.
Careful storage is needed when handling sodium hydroxide for use, especially bulk volumes. Following proper NaOH storage guidelines and maintaining worker/environment safety is always recommended given the chemical's burn hazard.
Sodium hydroxide must be stored in airtight containers to preserve its normality as it will absorb water from the atmosphere.