Carboxylic Acids Acidity: Overview, Questions, Preparation

Carboxylic acids get separated when put in water, thus forming carboxylate ions and hydronium ions. Carboxylate ions stay stable because they contain negative charges, which help in effective delocalization in water and maintain the acetate ion’s resonance structure.

The carboxylic acid acidity can be derived from the nature of the alkyl, aryl, or alkenyl groups (commonly called R- Group) as they are attached to the carboxyl group. As mentioned above, the electron extraction and insertion can cause the acidity level to go up and down. It also ensures the effective and proper delocalization of the negative and positive charge through resonance.

1. Solubility: The hydroxyl and carbonyl groups form the carboxyl group. Small carboxylic acids are dissolvable or soluble in water as the concentration of the alkyl group present in them is small. On the other hand, large carboxylic acids are insoluble or have limited solubility when it’s compared with the first. This is due to the large concentration of the alkyl group present in it.

2. Boiling point: Compared to water, a carboxylic acid has a higher boiling point because it has a large surface area.

3. Acidity: Acidity present in carboxylic acids is greater than the phenols. Carboxylic acids are the organic acids, often referred to as weak acids, because they can partially separate in the water and form two solutions, i.e., H3O+ cations and RCOO− anions.

• It serves as a disinfectant.
• Formic acid is used as a reducing agent and for textile treatment.
• Acetic acid is used for the production of cellulose plastics and esters. 
• Methanoic acid has its applications in rubber, textile, dyeing, leather and electroplating industries.
• Hexanedioic acid’s usage is in the manufacture of nylon-6, 6.
• Oleic acid is applied in the manufacturing of soaps and detergents.
• Esters of benzoic acid are noted for their use in perfumery. 
• Acrylic acid is deployed for the production of acrylic esters and resins, which are primarily used in coatings and adhesives.
• Methacrylic acid acts as a raw material for the manufacture of ion-exchange resins.

• Homovanillic acid and vanillylmandelic acids, present in body fluids, are helpful for diagnosing neurological disorders.
• The drugs containing carboxylic acid groups like aspirin and phenacetin are used to treat pain and diseases.
• They have a variety of applications in the preparation of cosmetics. Palmitic acid and stearic acid are examples of acids used in cosmetics, soaps, candles and pharmaceutical products.
• They act as solubilizers for modifying the solubility and lipophilicity of antibiotic drugs.
• Alpha-hydroxy acids play a vital role in skin whitening and the treatment of acne.

• They are naturally available in fruits and vegetables, like malic acids in grapes and apples, oxalic acids in parsley and broccoli and citric acids in citric fruits.
• Some of the acids are added as preservatives (lactic acid, sodium benzoate), emulsifiers (tartaric acid), antioxidants (ascorbic acid) and as flavours (propionic acid).
• Ethanoic acid is used as a solvent and as vinegar.
• Some of the carboxylic acids, like folic and nicotinic acid, act like vitamins for microbial nutrition.

The topic is under the chapter ‘Aldehydes, ketones and carboxylic acids’. By the end of the unit, one can distinguish the functional groups and IUPAC names of aldehydes, ketones and carboxylic acids. Also, learn their structure, preparation, properties and uses. Multiple-choice questions from this topic are more common in the NEET exams. As per the current year 2021, the chapter - Aldehydes, Ketones & Carboxylic acid holds a weightage of 3-4 marks for Class 12.

1. Give the IUPAC names of the following compounds: (i) Ph CH2-CH2-COOH (ii) (CH3 ) 2-C=CH-COOH

Answer: (i) 3-phenyl propanoic acid (ii) 3-Methyl but-2-enoic acid

2. To which of the following groups does soap belong?

i) Esters ii) Amines iii) Salts of organic higher fatty acids iv) Aldehydes

Answer: Salts of organic higher fatty acids

3. Find the wrong statement from the below.

i) Oxalic acid used for making metal polish

ii) Benzoic acid used in the manufacture of dyes

iii) Oxalic acid in the form of ferrous potassium oxalate used as a developer in photography

iv) Benzoic acid as a disinfectant

Answer: iv) Benzoic acid, which is used as a food preservative and in antiseptic and dyes.

4. The following illustration explains the structure of the carboxyl group. As you can understand from the structure below, the carbon bonds to the group lie on the same plane but separated by 120 degrees -

5. The following example explains the process of preparation of carboxylic acid with the help of alkylbenzenes - 

6. The following diagram consists of two physical properties/traits of carboxylic acids. The first one can be used to understand the structure when in a vapour state, and the second one when the bonding of carbons is miscible with water -

[Image courtesy: NCERT]