Registration Dossier

Physical & Chemical properties

Additional physico-chemical information

Administrative data

Link to relevant study record(s)

Description of key information

NaOH is a strong alkaline substance that dissociates completely in water into the sodium ion (Na+) and hydroxyl ion (OH-). The dissolution/dissociation in water is strongly exothermic, so a vigorous reaction occurs when NaOH is added to water (EU RAR 2007; section 1.3, page 7).

Additional information

In the OECD SIDS document of 2002 (section 2.14, page 40) following addition physico-chemical information is specified:

- Clayton et al (1982)

Sodium hydoxide is soluble in aliphatic alcohols and glycerine. NaOH is a hygroscopical product and sensible to
the air carbon dioxide.

- Environment Canada (1984) NaOH is highly soluble in water and dissociates to sodium and hydroxide ions, with the effect of increasing pH an alkalinity. In water the anhydrous form sinks (specific gravity of 2.13 at 20°C), dissolves, mixes with water and hydrates exothermically.

- OxyChem (2000)

The heat of solution of NaOH is high. The high heat of solution generates a large amount of heat which can cause local boiling or spurting when adding sodium hydroxide to water or any solution. When making solutions, always add the caustic soda to the water surface with constant stirring and never add water to caustic soda.