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Acetic acid is an organic substance in the carboxylic acid family. Acetate is a salt, ester, or acylal of acetic acid that is produced by the fermentation and oxidation of naturally occurring carbohydrates.
- Acetic acid is required for making cellulose acetate, vinyl acetate, plastics, photographic films, textiles, and volatile organic esters.
- They are frequently used as solvents for resins, paints, and lacquers
- This acid is also used in the preparation of metal acetates, which are used as an important material in some printing processes.
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Key Terms: Acid, Metal, Ethanoic Acid, Solvent, Acetic Acid, Methyl Group
What is Acetic Acid?
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An organic substance having the chemical formula CH3COOH is acetic acid. It is a carboxylic acid with a functional group of carboxyl linked to a methyl group. The chemical formula for acetic acid is C2H4O2, and its systematic IUPAC name is ethanoic acid.
- A mixture of acetic acid and water, vinegar has a volume percentage of ethanoic acid ranging from 5% to 20%.
- The acetic acid that is found in it gives it a strong scent and sour flavour.
- Glacial acetic acid is a term used to describe an undiluted acetic acid solution.
- At temperatures below 16.6oC, it develops crystals that resemble ice.
- Being a polar, protic solvent, it has several uses.
- Glacial acetic acid is frequently used in analytical chemistry to calculate weakly alkaline compounds.
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Structure of Acetic acid
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In a solid form of acetic acid, a chain of molecules is seen where each molecule is joined to the next by a hydrogen bond. At temperatures of about 120o, ethanoic acid dimers can be detected in the vapour phase.
When ethanoic acid is present in a diluted solution, its dimers can be detected even in the liquid phase.
- Solvents that encourage hydrogen bonding have a negative impact on these dimers.
- Acetic acid's chemical formula is CH3(C=O) OH or CH3CO2H.
The following diagram shows acetic acid's structure.
Diagrammatic representation of acetic acid
The second-simplest carboxylic acid in terms of structure is ethanoic acid, which is basically a methyl group with a carboxyl functional group connected to it. The simplest carboxylic acid is formic acid, HCOOH.
Acetic Acid as a Solvent
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In its liquid state, CH3COOH is a protic solvent that is both polar and hydrophilic (easily dissolves in water). In this way, acetic acid and water mixtures are comparable to ethanol and water mixtures. Moreover, acetic acid mixes readily with hexane, chloroform, and a number of oils. Yet it does not combine miscible with long-chain alkanes (such as octane).
Acetic acid is a highly significant industrial solvent due to its advantageous solvent characteristics and capacity to mix miscible with both polar and nonpolar chemicals. It is extensively utilised in the production of dimethyl terephthalate (DMT).
Physical Properties of Acetic Acid
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While being regarded as a weak acid, concentrated ethanoic acid has significant corrosive properties and may even harm human skin if exposed to it. The following is a list of acetic acid's general characteristics.
- Ethanoic acid seems to be a colourless liquid and has a strong scent.
- Ethanoic acid has melting and boiling temperatures at STP of 289K and 391K, respectively.
- Acetic acid has a molar mass of 60.052 g/mol and a liquid density of 1.049 g/cm-3.
- Ethanoic acid's carboxyl functional group has the potential to ionise the chemical, as shown by the following reaction: CH3COOH ⇌ CH3COO - + H + Ethanoic acid
- The primary reason acetic acid is acidic is due to the proton release mentioned by the equilibrium process above.
- Ethanoic acid has an acid dissociation constant (pKa) of 4.76 in a solution of water.
- Acetic acid's conjugate base, acetate, is produced through the reaction CH3COOH + H2O ⇌ CH3COO- + H3O+
- A 1.0M concentration of ethanoic acid has a pH of 2.4, which suggests that it does not entirely dissociate.
- Acetic acid has a dielectric constant of 6.2 and is a polar, protic solvent when it is liquid.
In many animals, the binding of acetic acid to coenzyme It serves as the main catalyst for the metabolism of lipids and carbohydrates. Typically, the interaction between methanol and carbon monoxide produces this molecule (carbonylation of methanol).
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Chemical Properties of Acetic Acid
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Acetic acid experiences chemical reactions that are comparable to those of other carboxylic acids. The following chemical equations describe how this molecule decomposes at temperatures over 440oC to produce either methane and carbon dioxide or water and ethenone.
CH3COOH + Heat → CO2 + CH4
Heat + CH3COOH → H2C=C=O + H2O
When exposed to acetic acid, several metals, such as magnesium, zinc, and iron, corrode. Acetate salts are created as a result of these interactions.
Mg (CH3COO)2 (magnesium acetate) + H2 = 2CH3COOH + Mg
According to the chemical equation shown above, the reaction between ethanoic acid and magnesium produces magnesium acetate and hydrogen gas.
Uses of Acetic Acid
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In the daily activities of humans, ethanoic acid plays a crucial role as an organic component. This is a list of some of acetic acid's key applications.
- Since it has antibacterial properties, acetic acid is utilised as an antiseptic.
- Ethanoic acid is used in the production of rayon fabric.
- Acetic acid has been used medically to cure cancer by injecting it right into the tumour.
- As it makes up the majority of vinegar, it is used to pickle a variety of vegetables.
- Ethanoic acid is used in the production of rubber.
- It is also used in the production of several fragrances.
- It is frequently used in the creation of VAM (vinyl acetate monomer).
- Acetic anhydride is the end product of the condensation process between two acetic acid molecules.
Popular Uses of Acetic Acid
There are several uses for acetic acid. As a result, the acid is employed in many other applications in addition to being used as a food preservative (vinegar). Some of the most popular and significant uses are as follows:
Use in Industry
Acetic acid is a chemical reagent used to create a range of chemical compounds including acetic anhydride, ester, vinyl acetate monomer, vinegar, and a variety of other polymeric materials. Acetic acid is also utilised in numerous industrial processes to create substrates. It can be used to purify organic compounds since it can be used as a solvent for recrystallization.
Usage in Medicine
Many medical procedures employ acetic acid. Its main use is as an antiseptic against germs such staphylococci, enterococci, streptococci, and pseudomonas. Also, it is employed in the diagnosis of infections and the detection of cervical cancer.
Industry of Food
In the food industry, acetic acid is most frequently employed in industrial pickling processes and condiments including mayonnaise, mustard, and ketchup. Moreover, it is used to season a variety of dishes, including salads. Also, when vinegar and alkaline substances like baking soda react, a gas is produced that helps baked items puff up.
Usages at Home
Acetic acid is frequently used as vinegar and comes in the form of a dilute solution. And as we all know, vinegar is frequently employed in households for a range of tasks, including cleaning, doing laundry, cooking, and many others. Farmers use acetic acid to cow silage in order to prevent bacterial and fungal development.
Preparation of Acetic acid
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Carbonylation of methanol results in the industrial production of acetic acid. Here are the chemical equations for each of the three phases in this procedure.
HI (hydrogen iodide) + CH3OH (methanol) → CH3I (methyl iodide intermediate) + H2O
CO (carbon monoxide) + CH3I → CH3COI (acetyl iodide)
Acetic acid (CH3COOH) + HI = CH3COI + H2O
In this instance, methanol and hydrogen iodide react to produce a methyl iodide intermediate. The acetic acid product is then produced by reacting this intermediate with carbon monoxide and treating the resultant chemical with water. It is essential to remember that step 2 of this method requires the employment of a metal carbonyl complex as a catalyst.
Other Methods of Preparing Acetic Acid
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Cobalt, chromium, and manganese naphthalene salts can be used as metal catalysts in the oxidation of acetaldehyde. This reaction's chemical equation looks like this:
2CH3CHO + O2 → 2CH3COOH
The following chemical reaction describes the oxidation of ethylene (C2H4) to acetic acid in the presence of a palladium catalyst and a heteropoly acid.
C2H4 + O2 → CH3COOH
Certain anaerobic microorganisms may easily convert sugar into acetic acid.
C6H12O6 → 3CH3COOH
It should be emphasised that these bacteria's anaerobic fermentation of sugar does not result in the formation of any ethanol intermediates.
Things to Remember
- The molar mass of acetic acid is calculated to be 60.05 g/mol.
- Acetic acid has a melting point of 289.5K, or 16.5°C. Below this temperature, it cools and crystallises into ice.
- The production of several colours, polymers, rayons, silk, and fragrances all include the usage of ethanol.
- It works against the majority of other bacteria and is an active micro bactericidal disinfectant.
- Acetic acid is helpful in the production of esters, acetone, and acetate, all of which are employed in different sectors.
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Sample Questions
Ques. Acetic acid ___________. (3 Marks)
(a) Is insoluble in water
(b) Is pale yellow in colour
(c) Turns blue litmus red indicates its acidic
(d) None of the above
Ans. The Correct option is c) Turns blue litmus red indicates its acidic
Explanation: Acetic acid is extensively soluble in water, however most of the substance dissolves into molecules, leaving it a weak electrolyte. It exhibits an acidic reaction by turning blue litmus paper red. Due to the fact that it does not fully dissociate in aqueous solution, it is a weak acid.
Acetic acid, commonly referred to as ethanoic acid, is an organic chemical substance well known for imparting vinegar's sour flavour and strong odour. It is colourless.
Ques. Write down a test to distinguish between pentan-2-one and pentan-3-one. (2 Marks)
Ans. The iodoform test can be used to distinguish between pentan-2-one and pentan-3-one. Since pentan-2-one has a -CO-CH3 group, it precipitates iodoform into a yellow substance. Pentan-2-one and pentan-3-one do not have a -CO-CH3 group, although pentan-2-one has a positive iodoform test result.
Ques. Carbon-carbon bonds must be broken in order for ketones to oxidise. List the by-products of 2, 5-dimethylhexan-3-one oxidation. (2 Marks)
Ans. The combinations of ketone and carboxylic acids produced by the oxidation of 2, 5-dimethylhexan-3-one are the end products. Carboxylic acids are then produced by further oxidising ketones. Overall, 2-methylpropanoic acid, 3-methylbutanoic acid, ethanoic acid, and methanoic acid are the results of this process.
Ques. Although carbonyl groups are present in carboxylic acids, unlike aldehydes or ketones, they do not exhibit the nucleophilic addition process. Why? (3 Marks)
Ans. In a carbonyl molecule, the oxygen atom pulls more shared pairs of electrons towards it, giving carbon a partial positive charge while giving oxygen a partial negative charge. Therefore, a nucleophile attacks the carbon in the carbonyl atom. Resonance prevents carbonyl-containing carboxylic acids from exhibiting the nucleophilic addition reaction like aldehydes or ketones.
Ques. Why is glacial acetic acid destructive to the environment? (2 Marks)
Ans. Just 1% water and 99.5 percent pure acetic acid make up the extremely concentrated form of glacial acetic acid. It gets quite corrosive when the amount of acid in it increases. With a temperature of 118 degrees Celsius, the boiling point of glacial acetic acid is unusually high.
Ques. How will you determine whether acetic acid is acidic? (3 Marks)
Ans. A pH scale is used to assess a compound or solution's nature. Using this metric, solutions are tested using litmus paper. The substance is acidic if it causes the blue litmus paper to turn red. If the compound converts the red litmus paper into blue, then the chemical is basic. Using blue litmus paper, acetic acid's acidity is determined. As it causes the blue litmus paper to become red, acetic acid is an acidic substance.
Ques. What are the dangers of acetic acid? (3 Marks)
Ans. The use of acetic acid carries a number of risks, including
- Acetic acid can be harmful and, in rare circumstances, can result in serious wounds and burns if exposure is sustained.
- Acetic acid can enter the airways fast and irritate them for a period in those who are experiencing respiratory distress, making them more vulnerable to issues.
- Acetic acid can irritate the throat and make breathing difficult if consumed or inhaled by the user. The user has to visit a doctor in these situations and receive the required medical care right away.
Ques. Are there any alternative ways to make acetic acid? (5 Marks)
Ans. Indeed, some cobalt, chromium, and manganese salts of naphthalene can act as metal catalysts in the oxidation of acetaldehyde. Such a reaction's chemical formula will be:
2CH3CHO + O2 → 2CH3COOH
The following chemical reaction describes the oxidation of ethylene (C2H4) to acetic acid in the presence of a palladium catalyst and a heteropoly acid:
O2 + C2H4 = CH3COOH
Certain anaerobic microorganisms may quickly transform sucrose into acetic acid.
3CH3COOH = C6H12O6
It should be emphasised that no ethanol intermediate is produced when these bacteria digest sugar anaerobically.
Ques. What roles does acetic acid play in the creation of chemicals? (5 Marks)
Ans. Acetic acid has a wide range of applications in chemical synthesis, including the following:
- Making cellulose acetate, a material used in the production of textiles and photographic films, requires the usage of acetic acid.
- The production of terephthalic acid benefits from the use of acetic acid as a solvent. The method is known as the Amoco method. Oxidation of p-xylene results in terephthalic acid. PET, a material often used to make plastic bottles, is created using terephthalic acid.
- When reacting with different alcohols to create esters, acetic acid is particularly helpful. Derivatives of acetic acid ester are widely utilised as food additives.
- Vinyl acetate monomer is created using acetic acid. The polymerization of this monomer produces poly (vinyl acetate), generally known as PVA. PVA is used in a variety of industries, including the manufacturing of paper and medicine, because of its biocompatibility with nanotechnology (as a stabilising agent).
- Several organic catalytic processes benefit from the use of acetic acid as a solvent.
Ques. What are ethanoic acid's physicochemical characteristics? (5 Marks)
Ans. Ethanoic acid is a colourless, odourless liquid with a strong aroma. As it is a lower carboxylic acid, ethanoic acid is liquid at normal temperature.
Because ethanoic acid is completely soluble in water, vinegar is made from it. The solubility of acids in water declines with an increase in their molecular weight. Acetic acid freezes at 290 K; at this threshold, it crystallises to produce glacial acetic acid.
Ethanoic acid has a boiling point of 391 K. Acetic acid has a density of 1.05 g cm-3. Its density exceeds that of water, which is 1g cm-3. Having an ethanoic acid pH of 2.4. Acetic acid is polar and has a dielectric constant of 6.2 when it is liquid. The dielectric constant of acetic acid, a polar protic solvent, is 6.2. At 25°C, ethanol's dissociation constant is 4.76.
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