What Is Formalin? Key Properties, Composition, and Applications
Formalin is another name for formaldehyde. Following a previous trade name, "formalin," "formaldehyde" was first used as a generic trademark in 1893. The simplest aldehyde is formaldehyde, which has the formula CH2O and is made up of hydrogen, carbon, and oxygen. At room temperature, formaldehyde is one of a wide group of chemicals known as volatile organic compounds, which evaporate and become gaseous.
Formalin Composition
Formalin is a water-based saturated solution of formaldehyde gas. It contains about 40% formaldehyde gas (by volume) or 37% formaldehyde gas (by weight), as well as a small amount of stabilizer. The general stabilizer, in this case, is 10-12 percent methanol, which helps to avoid formaldehyde polymerization. Formaldehyde solution is very unstable without a stabilizer, and it appears to polymerize, forming insoluble macromolecules. Methylene glycol is the main product of the complete hydration of formaldehyde gas. Polymerization results in the development of paraformaldehyde as a result.
Formalin Chemical Properties
Formalin is a colourless liquid. Due to formaldehyde off-gassing, it has a strong, irritating odour. Since the PH of this solution is neutral, it can be used as a reducing agent to reduce other substances when making formic acid. Formalin solutions with a high concentration of formaldehyde are flammable. Since they can destroy dangerous microorganisms, this solution can be used as disinfectants and germicides. Aside from that, they have a dehydrating effect, the ability to preserve themselves, and the ability to combine with proteins, inactivating them and destroying cells. Formalin is widely used in aquariums to destroy parasites that live on fish because of these properties.
Synthesis of Formalin
When formalin reacts with a base, such as sodium hydroxide, sodium formate and methanol are produced. The chemical formula is shown below.
2HCHO + NaOH → HCOONa + CH3OH
When formaldehyde reacts with ammonia, formamidine and water are produced. The chemical formula is shown below.
6HCHO + 4NH3 → (CH2)6N4 + 6H2O
Uses of Formelene
Formalin solution can be used as a disinfectant because it destroys most bacteria and fungi (including their spores). Toxins and viruses are inactivated using it as an ingredient in vaccine production. In personal care products like cosmetics, formaldehyde releasers are used as biocides. They are known to cause allergic contact dermatitis in some sensitized individuals, despite being present at levels that are not usually considered dangerous.
It's used to create resins like urea formaldehyde and phenol-formaldehyde, which are used in foundries to make cores and molds.
It's used as a disinfectant, fungicide, fumigant, and preservative in agriculture and medicine.
A broad range of products, especially building materials, contain formaldehyde.
Importance and Uses of Formalin
A carbon atom with an atomic number of 6has 4 electrons on its outer valence shell. So it can combine with many other elements and form different types of compounds. The number of types is so vast because carbon atoms can form chains by combining with each other. Hydrocarbons are the most famous among all the compounds formed by carbon. Hydrocarbons are the compounds formed by a combination of mostly carbon ( C ), Hydrogen (H) Oxygen (O), and some other less frequently combining elements such as Nitrogen (N), Sulphur (S), Phosphorus (P), etc. It is also interesting to note that because of such immense types of hydrocarbons found in nature and its importance in the working of nature these are studied in a whole separate branch of chemistry known as organic chemistry.
In Organic Chemistry, we learn about different groups of hydrocarbons based on the type of bond they create while bonding with each other and forming chains. Examples are methane group, methylene group, methine group, etc. It also depends on the different types of substrates arched to the carbon chains. Aldehydes are one such group with Oxygen attached to one carbon atom at the end by a double bond. The first compound in this group formed by a single carbon atom bonded with two hydrogen atoms and one Oxygen atom is termed formaldehyde. It usually remains in a gaseous state at room temperature but can also be found dissolved in water. The water that contains dissolved formaldehyde is known as formalin. It is easily identifiable in laboratories due to its irritating smell or odor and is used as a disinfectant or germicide.
FAQs on Formalin: Structure, Uses, and Synthesis
1. What is formalin and what is its composition?
Formalin is the commercial name for an aqueous solution of formaldehyde. It typically contains 37-40% formaldehyde (HCHO) by mass or volume. To prevent the formaldehyde from polymerising and precipitating out of solution, a small amount of methanol (about 10-15%) is often added as a stabiliser.
2. What is the key difference between formaldehyde and formalin?
The primary difference lies in their physical state and composition. Formaldehyde (HCHO) is a pure, colourless, pungent-smelling gas at room temperature. Formalin, on the other hand, is not a pure substance but a solution; it is formaldehyde gas dissolved in water. Essentially, formaldehyde is the chemical compound, while formalin is its most common commercial form.
3. What are the main industrial applications of formalin?
Formalin is a crucial chemical with diverse industrial uses, primarily due to the reactivity of formaldehyde. Its main applications include:
- Manufacturing Resins: It is a key ingredient in producing thermosetting resins like Urea-formaldehyde (used in adhesives and particleboard) and Phenol-formaldehyde (Bakelite).
- Chemical Synthesis: It serves as a building block for many other complex organic chemicals.
- Preservation: Widely used for embalming in mortuaries and preserving biological specimens in laboratories.
- Disinfection: It acts as a powerful disinfectant and biocide to sterilise equipment and areas.
4. How is formalin prepared on an industrial scale?
Industrially, formalin is produced through the catalytic oxidation of methanol (CH₃OH). In this process, methanol vapour is mixed with air and passed over a heated metal catalyst, typically silver or an iron-molybdenum oxide mixture, at high temperatures (around 600-700°C). The methanol is oxidised to form formaldehyde gas, which is then rapidly cooled and absorbed into water to create the final formalin solution.
5. How does formalin act as a preservative for biological specimens?
Formalin's preservative action stems from its ability to cross-link proteins. The active ingredient, formaldehyde, reacts with the amino groups (-NH₂) in the amino acids of proteins. This forms stable methylene bridges between protein molecules, a process known as fixation. This cross-linking hardens the tissue, inactivates decaying enzymes, and kills microorganisms, thus preventing decomposition and maintaining the structural integrity of the specimen.
6. Why is formalin considered a hazardous substance for humans?
Formalin is classified as a hazardous substance due to the toxicity of formaldehyde. It is a known human carcinogen, linked to nasopharyngeal cancer and leukaemia. Short-term exposure can cause severe irritation to the skin, eyes, nose, and throat. Inhaling its vapours can lead to respiratory distress, and ingestion can be fatal.
7. What chemical change occurs when a bottle of formalin is left standing for a long time?
When formalin is stored, especially at low temperatures, the dissolved formaldehyde molecules undergo a polymerisation reaction. They link together to form a long-chain polymer called paraformaldehyde, which is a white, solid precipitate. This reduces the concentration of active formaldehyde in the solution. To slow down this process, methanol is added as a stabiliser.
8. What is the importance of using 'neutral buffered formalin' in histopathology?
In histopathology (the microscopic study of diseased tissue), standard formalin can slowly oxidise to form formic acid. This acid reacts with haemoglobin in blood-rich tissues to create an undesirable black-brown 'acid formalin hematin' pigment, which obscures cellular details under a microscope. To prevent this, a buffer (like phosphate) is added to create 10% Neutral Buffered Formalin (NBF). This maintains a neutral pH, preventing pigment formation and ensuring the tissue is perfectly preserved for accurate diagnosis.
