Forms
Formaldehyde is more complicated than many simple carbon compounds because it adopts different forms.
One important derivative is the cyclic trimer metaformaldehyde or trioxane (CH2O)3. There is also an infinite polymer called paraformaldehyde.
When dissolved in water, formaldehyde combines with water to form methanediol or methylene glycol H2C(OH)2. The diol also exists in equilibrium with a series of oligomers (short polymers), depending on the concentration and temperature.
A saturated water solution, that contains about 40% formaldehyde by volume or 37% by mass, is called "100% formalin". A small amount of stabilizer, such as methanol, is usually added to limit oxidation and polymerization. A typical commercial grade formalin may contain 10–12% methanol in addition to various metallic impurities.
Read more about this topic: Formaldehyde
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