What is Acetic Acid?
Acetic acid is an organic compound belonging to the carboxylic acid group. Its formula is CH₃COOH where a methyl group is attached to a carboxyl functional group. Its IUPAC name is ethanoic acid. Acetic acid is the main constituent of vinegar and has been known since ancient times. Vinegar solution contains acetic acid and water where ethanoic acid is between 5% and 20% by volume. The acetic acid in vinegar is responsible for its pungent smell and sour taste.
It is made from the fermentation and oxidation of natural carbohydrates; acetate is an acetic acid salt, ester, or acylal. Acetic acid is used to make metal acetates, which are used in some printing processes; vinyl acetate, which is used to make plastics; cellulose acetate, which is used to make photographic films and textiles; and volatile organic esters (such as ethyl and butyl acetates), which are widely used as solvents for resins, paints, and lacquers. Acetic acid is a biologically significant metabolic intermediary that can be found in bodily fluids and plant juices.
Glacial acetic acid is an acetic acid solution that has not been diluted. At temperatures below 16.6 degree Celsius, it produces crystals that resemble ice. It has a wide range of applications as a polar, protic solvent. In the realm of analytical chemistry, glacial acetic acid is commonly used to assess weakly alkaline compounds.
Acetic acid also has various other important uses. Here, we will also learn about the physical and chemical properties of acetic acid.
Structure of Acetic Acid
Ethanoic acid is the second simplest carboxylic acid. Here is the structure of acetic acid.
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The structure of ethanoic acid is given by CH₃COOH.
In the solid-state of acetic acid, there is a chain of molecules with individual molecules connected through hydrogen bonds.
In its vapour state, its dimers are found at a temperature of about 120℃°.
When in the liquid phase, its dimers are found when present in a dilute solution.
CH₃COOH Molar Mass
By calculation, the molar mass of acetic acid comes out to be 60.05 g/mol. It can be calculated as:
(2 × 12.011) + (4 × 1.00794) + (2×15.999) g/mol
= 60.05 g/mol
Physical Properties of Acetic Acid
Some important physical properties of acetic acid are listed below:.
Ethanoic or acetic acid has a pungent vinegar odour and sour taste.
It is a colourless liquid.
It boils at 391K.
Its density in liquid form is 1.049 g/cm³.
It can mix with water, alcohol, ether in all proportions.
In water, it dissolves with the evolution of heat and contraction in volume.
It is corrosive in nature and produces blisters when in contact with the skin.
Sulphur, iodine, and many other organic compounds are dissolved in it.
Acetic Acid Melting Point
The melting point of acetic acid is 289.5K or 16.5°C.
On cooling below this temperature, it forms ice-like crystals. Therefore, pure and anhydrous acid is usually referred to as glacial acetic acid whereas glacial means ice-like.
Chemical Properties of Acetic Acid
Some important chemical properties of acetic acid are given below:
The carboxyl functional group in ethanoic acid causes ionization of the compound, given by the reaction: CH₃COOH ⇌ CH₃COO⁻ + H⁺
The acidic quality of acetic acid comes from the release of the proton, described by the equilibrium reaction above.
In a solution of water, the acid dissociation constant (pKa) of ethanoic acid is 4.76.
CH₃COO⁻, acetate is the conjugate base of acetic acid.
Acetic acid doesn't dissociate completely as it can be seen that the pH of an ethanoic acid solution of 1.0M concentration is 2.4.
Acetic acid is a polar, protic solvent, with a dielectric constant of 6.2 in its liquid form.
Acetic Acid Reactions
Acetic acid undergoes nearly all carboxylic acid reactions.
Acetic acid undergoes decomposition when heated above 440°C to yield either methane and carbon dioxide or water and ethanone, given by the equations.
CH₃COOH + Heat → CO2 + CH4
CH₃COOH + Heat → H2C=C=O + H2O
When exposed to acetic acid, some metals such as magnesium, iron, and zinc undergo corrosion. This reaction leads to the formation of acetate salts. When magnesium reacts with acetic acid, it gives magnesium acetate and hydrogen given in the equation.
2CH₃COOH + Mg → Mg(CH₃COO)2 (magnesium acetate) + H2
2Ca + 2CH₃COOH—----> (CH₃COO)₂Ca (calcium acetate) +H₂
Acetate salts are formed when acetic acid reacts with alkalis as described in the equation.
CH₃COOH + KOH → CH₃COOK + H2O
Compounds formed in reaction with carbonates are acetate salts, water, and carbon dioxide.
2CH₃COOH + Na2CO3 (sodium carbonate) → 2CH₃COONa + CO2 + H2O
CH₃COOH + NaHCO3 (sodium bicarbonate)→CH₃COOHNa + CO2 + H2O
Ethanoyl chloride is formed when PCl₅ reacts with ethanoic acid.
Uses of Acetic Acid
Ethanoic acid is used in the manufacturing of various dyes, plastics, rayons, silk, and perfumes.
It is most simply used as table vinegar.
In medicines, it is used as a local irritant.
In the rubber industry, it is also used as a coagulating agent.
It is useful in the manufacturing of acetate, acetone, and esters used in various industries.
It is widely used in the production of VAM (vinyl acetate monomer).
In the treatment of cancer, it is directly injected into the tumour.
Acetic acid has desirable solvent properties, along with the ability to form miscible mixtures with both polar and nonpolar compounds. Hence, it is a very important industrial solvent. It is widely used in the industrial preparation of dimethyl terephthalate (DMT).
It is an active micro bactericidal disinfectant that is also effective against most other bacterias.
Acetic Acid's Most Important and Popular Applications
Acetic acid has a wide range of applications. As a result, in addition to being utilised as a food preservative (vinegar), the acid is used in a variety of applications. The following are some of the most common and important applications:
Use in Industry
Acetic acid is used in various industrial processes to make substrates and as a chemical reagent to make a variety of chemical compounds such as acetic anhydride, ester, vinyl acetate monomer, vinegar, and a variety of other polymeric materials. It may also be employed as a solvent for recrystallization, which makes it useful for purifying organic molecules.
Usage in Medicine
Acetic acid is used in a variety of medical applications. Its primary application is as an antiseptic against pseudomonas, enterococci, streptococci, staphylococci, and other bacteria. It's also used in the detection of cervical cancer and the treatment of infections.
Industry of Food
Acetic acid is most typically used in commercial pickling operations and condiments such as mayonnaise, mustard, and ketchup in the food business. It's also used to season a variety of foods, such as salads. Additionally, vinegar can react with alkaline chemicals like baking soda, releasing a gas that aids in the puffing up of baked goods.
Uses in the Home
Acetic acid, in the form of a weak solution, is widely used as vinegar. And, as we all know, vinegar is commonly used in the home for cleaning, laundry, cooking, and a variety of other purposes. To combat bacterial and fungal growth, farmers spray acetic acid on cattle silage.
FAQs on Acetic Acid – Properties, Reactions, and Uses
1. Mention some preparation methods of acetic acid.
Industrially, acetic acid is prepared by carbonylation of methanol. These two compounds react to form a methyl iodide intermediate which is then reacted with carbon monoxide. The resulting compound reacts with water to yield acetic acid. Here, the carbonyl complex is necessary as a catalyst in the second step. The equations of the preparation process are as follows:
CH₃OH (methanol) + HI (hydrogen iodide) → CH₃I (methyl iodide intermediate) + H₂O
CO (carbon monoxide) + CH₃I → CH₃COI (acetyl iodide)
H₂O+CH₃COI→ CH₃COOH (acetic acid) + HI
2. What are the hazards of acetic acid?
Though acetic acid is a weak acid, its concentrated form is corrosive to the skin which produces blisters and burns. Prolonged inhalation exposure about eight hours to acetic acid vapours at 10 ppm can produce some irritation of the eyes, nose, and throat. Lung irritation and possible damage to lungs, eyes, and skin may result at 100 ppm. Workers coming in contact with acetic acid for a long period can suffer from bronchitis, pharyngitis, erosion of exposed teeth, and conjunctivitis as well. So, mainly the hazard depends on the concentration of the acid.
3. What are the household uses of vinegar?
Acetic acid, in the form of a dilute solution, is widely used as vinegar. And, as we all know, vinegar is commonly used in the home for cleaning, laundry, cooking, and a variety of other purposes. To combat bacterial and fungal growth, farmers spray acetic acid on cattle silage. Acetic acid is a sour substance found in vinegar, pickled vegetables, and sauce, as well as a spice raw material.
