Final answer:
Formalin is not actually a hydrocarbon; it is an aqueous solution containing formaldehyde, which is an aldehyde. The presence of a carbonyl group (a carbon double-bonded to an oxygen atom) distinguishes formaldehyde HCHO from hydrocarbons, which consist solely of carbon and hydrogen. The functional group classification and the Lewis structure of formaldehyde outline its chemical identity separate from hydrocarbons.
Step-by-step explanation:
The question at hand is asking why formalin is considered a hydrocarbon, even though it contains oxygen. This question may arise from a misunderstanding regarding the definition of hydrocarbons. Hydrocarbons are organic compounds composed entirely of hydrogen and carbon. However, formalin is better categorized as an aldehyde rather than a hydrocarbon, specifically formaldehyde in aqueous solution.
Formaldehyde, with the molecular formula HCHO, is a simple aldehyde consisting of a single carbon atom double-bonded to an oxygen atom and two hydrogen atoms bonded to the carbon, completing its structure. Despite this molecule containing oxygen, its classification as an aldehyde comes from its functional group, which is characterized by the carbon atom double-bonded to the oxygen (carbonyl group) with a hydrogen atom attached to the carbon. This functional group defines aldehydes as a class of compounds within organic chemistry.
When formaldehyde is dissolved in water, it forms formalin, which is roughly 37% to 40% formaldehyde by weight. This solution is used extensively for embalming, preserving biological specimens, and sterilizing materials due to formaldehyde's ability to denature proteins and stop biological processes, thus preventing decay.
The Lewis structure of formaldehyde demonstrates that both the carbon and the oxygen atoms fulfill the octet rule, with the carbon atom having four bonding pairs and the oxygen atom having two bonding pairs and two lone pairs of electrons. This octet of electrons makes it an acceptable Lewis electron structure and also contributes to the stability and reactivity of the molecule, underlying its use in various applications such as embalming solutions.