Which gas is released when NaOH is dissolved?

Start >> Chemicals >> Inorganic acids / bases

Caustic soda

NaOH • aq

CAS 1310-73-2

Caustic soda

Sodium hydroxide solution

molar mass

density(Solution 40%) 
density (Solution 10%) 
Water solubility

39.997 g / mol (NaOH)

not specified
1.4299 g / cm3
1.1089 g / cm3
mixable in any ratio

Colorless, slightly viscous solution in higher concentrations

Use a plastic stopper and a suitable plastic bottle

Special notes for schools

Author's recommendations: For simple student experiments, it is recommended to use only the 3% solution. A 10% solution can also be used for experienced students in laboratory internships. The use of dilute solutions is also recommended in practical courses in upper school. Protective goggles, protective gowns and protective gloves are necessary at all concentrations. Even with dilute caustic soda there is the danger that you will miss a drop on a finger and rub your eyes with it later. This can cause serious eye irritation or serious damage. Therefore, after every work, hands and the workplace should be washed thoroughly with plenty of water, even with diluted caustic soda.

Risk assessment Germany (also EU)
GBU Working with sodium hydroxide and caustic soda

Security assessment of Switzerland

SB Working with sodium hydroxide and caustic soda

Effect on the human body

Caustic soda is corrosive to the skin and, even in relatively low concentrations, can damage the cornea and cause serious eye damage, including blindness.

Chemical properties

Sodium hydroxide is the name given to the aqueous, alkaline solution of sodium hydroxide. The dilution with water takes place with the development of heat. The concentrated caustic soda is a relatively heavy liquid.

When wood is stained or leached, the brown pigment in the wood is destroyed. In this way, old layers of paint can also be stripped off and old cabinets refreshed. Caution is advised when working with caustic soda on table tops, because even small splashes can cause significant color changes. If caustic soda is left in the air for a long time, it absorbs carbon dioxide from the air and gradually converts to sodium carbonate solution:

2 NaOH + CO2  N / A2CO3 + H2O
With hydrochloric acid, sodium chloride and water are formed in a neutralization reaction. When diluted with water, the density of caustic soda decreases. The specification for the density is important if you want to produce a dilute solution from a concentrated solution. In schools, concentrations of 3, 10 and 32 percent by mass, as well as the solutions 0.1 mol / l and 1 mol / l are most often required:

Concentration, mass percentage
Concentration, amount of substancedescriptionDensity at 20 ° C
50 %19.068 mol / lconcentrated1.5253 g / cm3
40 %14.300 mol / lconcentrated1.4299 g / cm3
32 %10.791 mol / lconcentrated1.3488 g / cm3
30 %9.958 mol / lconcentrated1.3277 g / cm3
20 %6.096 mol / ldiluted1.2192 g / cm3
10 %2.772 mol / ldiluted1.1089 g / cm3
3,9 %1.0 mol / l1 molar1.04 g / cm3
3 %0.774 mol / ldiluted1.0318 g / cm3
0,4 %0.1 mol / l0.1 molar1.00 g / cm3

If you put 10% caustic soda on the aluminum foil common in the household, this decomposes in a stormy reaction with the formation of sodium hydroxoaluminate and hydrogen. During the reaction, the aluminum foil is completely dissolved, giving off heat.

2 Al + 2 NaOH + 6 H2O 2 Na [Al (OH)4] + 3H2   

10% sodium hydroxide solution is applied to an aluminum foil
given. Little happens at first.

Then suddenly a stormy gas forms,
and the film dissolves.


In the laboratory, caustic soda is produced by dissolving sodium hydroxide in water while generating a lot of heat:

Sodium hydroxide + water N / A+-Ions + OH-Ions + water
NaOH + H2O N / A+ + OH + H2O

Balance and a volumetric flask to produce precise concentrations
Caustic soda is an important raw material for soap production. In the bakery, pretzel lye consists of around 4% caustic soda. The baker spreads this lye onto the lye biscuits before baking. This creates the typical lye taste after baking. The “drain free” cleaning agent contains sodium hydroxide, which forms caustic soda with water.

Sodium hydroxide is added to heated coconut oil, and curd soap forms after stirring.

Caustic soda is also used to clean oil and grease residues and to strip wood. In aluminum production it is used to break down bauxite, in paper production it is used to break down wood and straw fibers. The chemical industry needs them to produce sodium compounds. When dyeing the vat with indigo, caustic soda is also necessary.

Further information and media
The term lye and base
Demonstrations on the corrosivity of the fabrics
Working with drain cleaners in the household (including videos)
Student exercise: making curd soap using the hot method
Student exercise: Soap making by the cold process
Student exercise: dyeing with indigo
Manufacture of a pigment from vegetable dyes
Student exercise: the titration of caustic soda
Workbook: acids, alkalis, salts (for grades 8 or 9)
Digital foils: acids, bases, salts

Create an individual book: Basic text sodium hydroxide and caustic soda


> Table of Contents

© Thomas Seilnacht / User Manual / License Agreement / Imprint / Data Protection / Literature Sources