Description
SODIUM HYDROXIDE – SOLUTION 25% 30% 45% 50%
Solution pH: approximately 14 regardless of concentration
Density:
50%: 1.53 – 1.55 g/cm³
45%: 1.47 – 1.49 g/cm³
30%: 1.33 – 1.35 g/cm³
25%: 1.27 – 1.29 g/cm³
Caustic soda or sodium hydroxide (NaOH) is a strong, inorganic base with a monoclinic crystal structure. It is an ionic compound consisting of the sodium cation Na+ and the hydroxide anion OH-. Its solution is highly corrosive, colorless and odorless, which is slippery to the touch and can cause burns.
Sodium hydroxide solution is highly reactive and caustic, causing the corrosion of many metals (aluminium, zinc, copper) alongside the release of hydrogen. It also reacts with acids to form sodium salts, as well as with amphoteric metals. Sodium hydroxide solution is widely used in industry, e.g. in the production of detergents, water glass, soap, rubber, rayon and in water treatment processes. Sodium hydroxide solution should be handled carefully and stored appropriately to avoid reactions with carbon dioxide from the air, which can affect its properties. Depending on the concentration, it is classified as a substance presenting medium to low danger according to ADR regulations (UN number 1824).
On an industrial scale, sodium hydroxide solution is obtained by the chloralkali process, i.e. electrolysis of brine (sodium chloride solution). This process takes place in special electrolysers with a membrane or diaphragm, which allow the reaction products to separate. Moreover, the lime process can also be used, in which sodium carbonate (Na₂CO₃) reacts with slaked lime (Ca(OH)₂). However, this process is not very efficient. Initially, sodium hydroxide solution was obtained by the mercury process (mercury amalgam method), which was widely used before the introduction of more eco-friendly methods. The process involves the electrolysis of sodium chloride (NaCl) solution, as well as the reaction of sodium amalgam with water. However, the mercury process is banned in the European Union, but it is still carried out in some countries. This method is highly dangerous for the environment due to the toxicity of mercury, even small amounts of which can have serious effects on ecosystems and human health.
