Correct Answer - Option 3 : Paraformaldehyde
Concept:
- Formaldehyde is the simplest member of the family of carbonyl compounds and differs from other members in the respect that it has only one hydrogen atom attached to the functional group in place of an alkyl substituent.
- In the lab, it is prepared by the oxidation of methyl alcohol vapor and oxygen over copper or silver catalyst.
CH3OH + O2 → 2HCHO +2H2O
- Formaldehyde is a colorless gas with a pungent smell and can be easily condensed.
- It is very soluble in water and its aqueous solution is used as an antiseptic solution.
- Formaldehyde causes irritation to the eyes, skin, and nose.
- As formaldehyde is different from other aldehydes, it gives certain characteristic reactions that are not shown by other aldehydes. For example, formaldehyde on treatment with ammonia forms hexamethylenetetramine or urotropine.
Explanation:
Formalin:
- In the lab preparation of formaldehyde using methyl alcohol, vapors of methyl alcohol and air come in contact with heated platinized asbestos, where methyl alcohol gets oxidized to formaldehyde which is absorbed in water.
- The resulting mixture is called formalin. It is a mixture of about 40% formaldehyde, 8%methyl alcohol, and 52%water.
Polymerization of formaldehyde:
- Formaldehyde readily undergoes polymerization to give different products under different conditions.
- An aqueous solution of formaldehyde on evaporation leaves a crystalline substance with composition (HCHO)n. It is called paraformaldehyde.
nHCHO → (HCHO)n ( n = 6 to 100 )
Hence, formaldehyde polymerizes from 6 to 100 molecules to form Paraformaldehyde.
- When gaseous formaldehyde is allowed to stand at room temperature, it slowly polymerized to meta formaldehyde (HCHO)3 .
