Question

What is Formalin ?
A. Aqueous solution of $HCHO$ and $C{H_3}CHO$
B. Alcoholic solution of formaldehyde
C. $40\%$ aqueous solution of formic acid
D. $40\%$ aqueous solution of formaldehyde

Answer 1

Hint : The definition of Formalin is: It is a $40\%$ aqueous (water) solution of formaldehyde, which is a pungent gas, and has the chemical formula HCHO, which is used as an antiseptic, disinfectant and specially in today’s date as a fixative for the study of tissues under the microscope.

Complete step by step solution :
Let us know how formalin came into existence,
Formaldehyde is a naturally occurring organic compound which has the chemical formula $H - CHO$ . This pure compound is a pungent-smelling colourless gas which polymerises spontaneously into paraformaldehyde, hence there is a need to store it as an aqueous solution (formalin). It is the simplest of the aldehydes. It also contains $8\% C{H_3}OH$ and $52\% {H_2}O$ , with $40\%$ of Formaldehyde.
Hence, Formalin is a $40\%$ Aqueous solution of formaldehyde (option D).
Additional Information: Formalin is derived from formaldehyde which is one of the known cancer-causing agents. It is used for storing dead biological specimens for a long period of time (many years) and used in preserving bodies in mortuaries. And it also increases the life of fresh food. And therefore, it acts as a good preservative.
Formalin is also used in the manufacturing of vaccines, drugs and hard-gel capsules. For example, formaldehyde is used to inactivate viruses so they don’t cause disease, such as the influenza virus in making the influenza vaccine. Formalin has some side-effects that may include nausea, coughing and burning sensation in eyes, nose and throat in the short term, and it can cause cancer if consumed over a long period of time.

Note : A student should keep in mind that the composition of Formaldehyde in Formalin ranges between ( $37\% to 40\%$ ). Formaldehyde is a potent carcinogen that occurs in nature.