Introduction
Organic compounds such as aldehydes, ketones, and carboxylic acids are classified based on their functional groups. Aldehydes have the general formula RCHO, ketones are represented as RCOR, while carboxylic acids are written as RCOOH or RCO₂H.
In aldehydes, the carbonyl carbon is bonded to a hydrogen atom and double-bonded to oxygen. Ketones contain a carbonyl carbon bonded to two carbon atoms. Carboxylic acids, on the other hand, consist of a carbonyl group and a hydroxyl group attached to the same carbon atom, giving them unique chemical and physical properties.
What Are Carboxylic Acids?
Carboxylic acids are organic acids that contain the carboxyl functional group (–COOH). A common example is acetic acid, widely known as vinegar. The general formula for carboxylic acids is RCOOH.
These acids are found naturally in many plants and animals. Citrus fruits like oranges and lemons contain citric acid, while lactic acid is produced during fermentation and plays an important role in the food industry. The simplest members of this group include methanoic acid, ethanoic acid, and propanoic acid.
Structure of Carboxylic Acids
A carboxylic acid molecule has a central carbon atom bonded to:
- an –OH group through a single bond
- an oxygen atom through a double bond
- another carbon atom or hydrogen through a single bond
This structure allows strong hydrogen bonding, which explains many of their physical properties.
Common Examples
Some important carboxylic acids include acetic acid, propanoic acid, benzoic acid, valeric acid, palmitic acid, and stearic acid.
Fatty acids such as oleic acid and linoleic acid are present in both plants and animals. Amino acids, which contain both amino and carboxyl groups, are essential to life. Examples include histidine, leucine, lysine, methionine, tryptophan, and valine.
Butanoic acid is also naturally produced in human sweat glands and contributes to body odor.
Physical Properties
Carboxylic acids are usually colorless and have a sour taste. Lower carboxylic acids are liquids at room temperature, while higher ones are solids.
As the number of carbon atoms increases:
- melting and boiling points increase
- solubility in water decreases
They dissolve well in organic solvents like ethanol, toluene, and diethyl ether. Pure, water-free acetic acid is known as glacial acetic acid.
Naming of Carboxylic Acids
Carboxylic acids are named using IUPAC rules. The parent alkane name is taken and the suffix “oic acid” is added.
- CH₃COOH → ethanoic acid
- C₆H₅COOH → benzoic acid
For amino acids, the position of the amino group is indicated by numbering from the carboxyl carbon. For example, NH₂–CH₂–CH₂–COOH is named 3-aminopropanoic acid.
Chemical Properties
Carboxylic acids have relatively high boiling points due to strong intermolecular hydrogen bonding. They are weak Brønsted–Lowry acids, meaning they can donate one proton to form a carboxylate ion (RCOO⁻).
Their acidity varies depending on the attached groups. For example, oxalic acid has a pKa of 1.27, while benzoic acid has a pKa of about 4.2.
Uses of Carboxylic Acids
There are many important carboxylic acid uses across different industries.
They are widely used in the food industry—vinegar is a common preservative. Ethanoic acid derivatives are used in medicines like aspirin. Salicylic acid is a key ingredient in acne treatments.
Butanoic acid is used in making toothpaste, mouthwash, and lipsticks. Formic acid (methanoic acid) is used to coagulate rubber latex. Carboxylic acids also play a major role in the production of soaps, detergents, polymers, adhesives, perfumes, and artificial flavorings.
Understanding these applications helps students connect chemistry concepts to real life, which is why clear explanations like these are valuable for learners preparing for exams and even those enrolled in the best psle tuition in singapore, where foundational science knowledge is emphasized.
Summary
Carboxylic acids are an important group of organic compounds that contain the carboxyl functional group (–COOH). Along with aldehydes and ketones, they belong to the family of carbonyl compounds, but carboxylic acids are distinguished by having both a carbonyl group and a hydroxyl group attached to the same carbon atom. Their general formula is RCOOH. A common example is acetic acid, widely known as vinegar.
Carboxylic acids occur naturally in plants and animals. Citric acid is found in citrus fruits, lactic acid is produced during fermentation, and fatty acids such as oleic and linoleic acids are essential components of living organisms. Amino acids, which contain both amino and carboxyl groups, are the building blocks of proteins. These compounds play a crucial role in biological and industrial processes.
Physically, carboxylic acids are usually colorless and have a sour taste. Lower members of the group are liquids, while higher carboxylic acids are solids at room temperature. Their boiling and melting points increase with molecular size due to strong hydrogen bonding. As the carbon chain length increases, their solubility in water decreases, although they dissolve well in organic solvents.
Chemically, carboxylic acids are weak Brønsted–Lowry acids. They can donate one proton to form a carboxylate ion, and their acidity depends on the nature of the attached alkyl or aryl group. The strong hydrogen bonding also explains their relatively high boiling points.
There are many practical carboxylic acid uses in daily life. They are widely used in food preservation, medicines such as aspirin, skincare products, soaps, detergents, perfumes, polymers, and adhesives. Understanding these concepts helps students relate chemistry to real-world applications, which is especially useful for learners building strong science foundations, including those studying at the best psle tuition in singapore.
