Why are the NaOH solutions heated

Caustic soda

Sodium hydroxide is a solution of caustic soda (sodium hydroxide, NaOH) in water, regardless of its sodium hydroxide concentration.


Density of caustic soda

See: Caustic soda density table.


Storage and disposal

When handling and storing caustic soda, it should be noted that it reacts with the carbon dioxide in the air as well as with components of bottle glass. With the CO2 the air forms the lye Baking soda (Sodium hydrogen carbonate), which settles as a solid preferentially on the bottle caps:


NaOH + CO2 → NaHCO3.


Glass bottles with ground-glass stoppers can often only be opened with considerable effort due to the incrustations. You should therefore use tightly fitting plastic bottles and, if necessary, plastic stoppers.

The reaction products of the sodium hydroxide solution with the glass of the laboratory bottles can be recognized by white deposits on the inner walls.

Bottles resistant to alkalis should be used especially for storing caustic soda solutions of defined concentrations, such as for analytical chemistry, volumetry, etc.

Before disposing of the caustic soda, depending on its concentration, it must be diluted and neutralized with an acid (usually: hydrochloric acid).





Sodium hydroxide is a highly caustic and corrosive liquid in all concentrations and causes severe burns to the eyes and skin. Brief contact lasting just a few seconds can cause serious damage to the eye or even blindness. Only brief contact with the skin causes irritation or chemical burns.

In all cases, rinsing off with large amounts of running water is necessary immediately after body contact, if necessary under a safety shower or using eye rinsing showers. At workplaces where caustic soda is used, appropriate notices should be attached and reference should be made to the safety shower facilities.

Special precautionary measures must also be taken when preparing sodium hydroxide solution by dissolving sodium hydroxide in water or when diluting a sodium hydroxide solution. The process sometimes releases considerable energy in the form of heat, which can cause the caustic soda to heat up, splash, boil or even boil up explosively.

* Always add the solid sodium hydroxide or caustic soda to the water! Never add water to the sodium hydroxide solution or solid NaOH!

* The water should be lukewarm: temperature 27 ° C to 38 ° C. Under no circumstances should cold or hot water be used!

* The addition should be done slowly!


Updated on February 16, 2018.

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