(i) Formaldehyde:
(1) 40% solution of formaldehyde (formalin) is used for the preservation of biological specimens.
(2) To prepare bakelite (a phenol-formaldehyde resin), urea formaldehyde resin and other polymeric products.
(3) It is used as an insecticide.
(4) Formaldehyde forms urotropine which is used in medicines. It forms many dyes like indigo, rosaniline etc.
(ii) Acetaldehyde:
(1) Acetaldehyde is used primarily as a starting material in the manufacture of acetic acid, ethyl acetate, vinyl acetate, polymers and drugs.
(2) Acetaldehyde is used in the preparation of dyes and resins. It is used for the preparation of aromatic acids.
(3) It is used in pulverisation of the mirror.
(4) In the formation of medicine paraldehyde.