Acids are chemical molecules that are capable of donating a proton or receiving an electron pair in a chemical reaction. The Latin word “acid” which means sour was the first name of acid. Most of the acid molecule consists of a hydrogen atom bonded that can dissociate in water and form a cation and an anion.
The strength of an acidic molecule completely depends on its concentration of hydrogen ions. An acid that shows higher strength, produces more hydrogen ions. As a result, the value of pH becomes low in that solution.
The acidic substances are generally identified by their sour taste and they make the blue litmus paper to red color. Their pH values range between 0 – 6.
Definition of acids
Acids are important chemical molecules that have the ability to accept electron pairs and donate hydrogen protons. It has its own nomenclature system. The properties of acidic molecules depend on pH, taste, texture, reactivity, and conductivity.
Examples: Acetic acid (CH3COOH), Formic Acid (HCOOH), Hydrochloric Acid (HCl), Nitric Acid (HNO3), Perchloric Acid (HClO4), Phosphoric Acid (H3PO4), Sulphuric Acid (H2SO4), etc.
Properties of acids
The properties of acids are discussed below:
The acidic compound changes the color of blue litmus to red.
Acidic compound changes the color of Methyl Orange or Yellow to Pink
They convert Phenolphthalein from deep pink to colorless
They have a sour or tart taste
The pH level of acidic substances ranges from 0 to 6.
Acidic compound when reacts with alkaline compound, loses the acidic property.
They produce hydrogen gas when react with metal.
They destroy the base property when react with an alkaline compound.
The acidic compound reacts with the carbonate compound and produces carbon dioxide.
Acidic substances are corrosive in nature and corrode or rust metallic substances.
Theories of acid
Arrhenius Theory
According to this theory, acid is any chemical that produces an H+ ion in water and raises the H+ ion concentration in the solution is known as acid. Example: Hydrochloric acid (HCl) produces H+ in water when dissolved in water, Sulfuric acid (H2SO4) produces 2H+ in water when dissolved in water, and Nitric Acid (HNO3) produces H+ in water during dissociation.
HCl (aq) <—-> H+(aq) + Cl–(aq)
HNO3 (aq) < —– > H+ (aq) + NO3– (aq)
H2SO4(aq) <—> 2H+(aq) + SO42-(aq)
Bronsted Theory
According to this theory, an acid is defined as a donor of protons. The acid can release protons during dissociation and produces a higher concentration of H+ ions in the solution. Example: Hydrofluoric acid (HF) can produce H+ and HCl can produce H+.
HF < — > H+ + F–
HCl < —- > H+ + Cl–
Lewis Theory
According to this theory, acid is a compound that has the ability to take an electron pair. This acid contains electrophilic properties. Lewis Acids have empty orbitals and can accept electron pairs from Lewis bases. The chemical species with a trigonal planar structure and an empty p-orbital is responsible for accepting electron pairs from Lewis bases.
Examples are given below:
Classifications of acids
Classification of acids based on the source
The acid molecules are classified into two categories based on their sources namely organic acid and mineral acid.
Organic Acid: This acid is generally derived from organic materials such as plants and animals. They have the antimicrobial properties and stimulate the enzyme excretion in the gut. They help to supply the nutrients in the gut and develop the mucosal integrity. They are essential to enhance the pepsin and microbial phytase activity.
They induce pancreatic excretion and increase the protein digestion property in the gut. They improve the mineral’s utilization and reduce the competition between the microflora and the host. They develop the health conditions and rate of productivity.
Examples of their sources are oleic acid (Olive oil), Citric acid (Citrus fruits), Formic acid (Bee venom and ants), Oxalic acid (Rhubarb, spinach), Butyric acid (Milk, butter), Lauric acid (Coconut oil), Tartaric acid (Grapes, tamarinds, pineapples), Erucic acid (Rapeseed oil, Mustard oil), etc.
Mineral Acid: This type of acid is produced from mineral sources. Mineral acid is known as inorganic acid. Mineral acids are free from carbon. Mineral acid is highly soluble in water and insoluble in organic solvents. They show corrosive properties and are very much used in electrolytic cells. Examples: Hydrochloric acid (HCl), Nitric acid (HNO3), Phosphoric acid (H3PO4), Sulfuric acid (H2SO4), Boric acid (H3BO3), Hydrofluoric acid (HF), Hydrobromic acid (HBr), Perchloric acid (HClO4), Hydroiodic acid (HI), etc.
Classification of acids based on the presence of Oxygen
Acids are classified into two categories based on the presence of oxygen. They are Oxy-acids and Hydracids.
Oxy-acid: The acid that contains oxygen in its composition is known as Oxy-acid. Examples: Nitric acid (HNO3), Phosphoric acid (H3PO4), Sulfuric acid (H2SO4), Boric acid (H3BO3), etc.
Hydracid: The acid that contains hydrogen combined with other elements and does not contain any oxygen in its composition is known as Hydracid. Examples: HCl, HI, HBr, etc.
Classification of acids based on the Strength
The acids are classified into two types namely strong acids and weak acids based on their strength.
Strong Acid: An acid that can dissociate completely or almost completely in water is known as a strong acid. Examples: Nitric acid (HNO3), Phosphoric acid (H3PO4), Sulfuric acid (H2SO4), Boric acid (H3BO3), etc.
H+ + H2O <—-> H3O+
HCl (aq) <—-> H+(aq) + Cl–(aq)
HNO3 < —– > H+ + NO3–
H2SO4(aq) <—> 2H+(aq) + SO42-(aq)
Weak Acid: An acid that cannot dissociate completely or dissociates slightly in water is known as a weak acid. Examples: Acetic acid, Formic acid, Tartaric acid, etc.
HCOOH (aq) < —— > H+ (aq)+ COOH–(aq)
CH3COOH (aq)< —– > CH3COO–(aq) + H+(aq)
Classification basis on its concentration
The acids are generally two type’s namely concentrated acid and diluted acid.
Concentrated Acid: When an aqueous solution contains a higher percentage of acid is known as concentrated acid. Examples: Concentrated nitric acid, concentrated phosphoric acid, concentrated sulphuric acid, etc.
Diluted Acid: When an aqueous solution contains a lower percentage of acid is known as diluted acid. Examples: dilute sulphuric acid, dilute nitric acid, dilute phosphoric acid, etc.
Classification of acids based on the basic
There are generally three types namely monobasic acid, dibasic acid, and tribasic acid.
Monobasic Acid: This type of acid has only one hydrogen ion. Monobasic acid can attach with one hydroxyl group of the base to form salt and water. Examples: HI, HBr, HCl, etc.
Dibasic Acid: This acid produces two hydrogen ions in water per molecule. Example: Sulphuric acid (H2SO4)
H2SO4 (aq) < —- > 2H+ + SO42-
Tribasic Acid: The acid that produces three hydrogen ions in water per molecule is known as Tribasic acid. Example: Phosphoric acid (H3PO4)
NaOH(aq) + H3PO4(aq) <—> NaH2PO4(aq) + H2O(l)
Uses of Acids
Sulfuric acid is widely used to make batteries which are used in automobile engines. It is very much used to make dyes, explosives, paints, and fertilizers.
Nitric acid is used to make fertilizer, plastic, dye, explosives like TNT, and liquid fuel for rocket engines. Nitric acid is a very important chemical doping agent in electrochemistry.
Dilute HCl acid is used in various industries for heating purposes. It is also used to remove the scale of the boiler.
Acetic acid is widely used to increase the food flavor. It can be used for cleaning windows, floors, utensils, etc. Acetic acid removes the stains on woodwork. It can be used as a food preservative agent.
Citric acid extracted from orange juice and lemon juice can be used as a food preservative material.
Phosphoric acid is widely used for making fertilizer and detergent.
Boric acid is used to make glass, glazes and enamels, leather, paper, adhesives and explosives
Frequently Asked Questions (FAQs)
What is an acid in chemistry?
Acid is a chemical compound that has the ability to accept electron pairs and donate hydrogen protons.
What are the examples of acids?
Hydrochloric Acid (HCl), Nitric Acid (HNO3), Perchloric Acid (HClO4), Phosphoric Acid (H3PO4), Sulphuric Acid (H2SO4), etc.
What are the properties of acids?
The acid compound has the ability to change the color of blue litmus to red as well as change the color of methyl orange or yellow to pink. The pH value of acidic substances ranges from 0 to 6.
What are the uses of acids?
Acids are used very much to make fertilizers, dyes, explosives, paints, glass, glazes and enamels, leather, paper, adhesives, etc.
What are the types of acids?
Acids are generally two types based on their source namely organic acid and mineral acid. Based on the basicity, acids are three types namely monobasic, dibasic, and tribasic acid.
