Acid,Base and Salts

Previously, acids, bases, and salts were determined by examining their aqueous solutions. An acid is a substance that tastes sour in water, turns blue litmus red, and neutralises bases. A base is a substance whose aqueous solution tastes bitter, turns red litmus blue, or neutralises acids.

In aqueous solution, salt is a neutral substance that has no impact on litmus. Faraday defined electrolytes as acids, bases, and salts. Furthermore, Liebig proposed that acids are hydrogen-containing compounds that can be replaced with metals.

Acids

Acidity is a distinguishing property of acids. Aside from hydrochloric acid, our environment contains a wide range of acids. Citrus fruits like lemons and oranges contain citric and ascorbic acids, while tamarind paste contains tartaric acid. 

The words “acid” and “acidity” are derived from the Latin word “acidus,” which means “sour.” When put in acid, blue litmus paper turns red, however red litmus paper does not change colour. When acids react with certain metals, dihydrogen is produced.

Bases

Red litmus paper turns blue when exposed to  bases, whereas blue litmus paper remains blue. They have a soapy texture and a harsh taste. Another example of a base is sodium bicarbonate, which is used in cooking, and household bleach.

Salts

Sodium nitrate, barium sulphate, and potassium chloride are also common salts. When hydrochloric acid (acid) reacts with sodium hydroxide, sodium chloride, often known as common salt, is formed (base). In solid sodium chloride, electrostatic forces keep a cluster of positively charged sodium ions and negatively charged chlorine ions together.

Dissociation And Ionisation

When a solid ionic substance dissolves in water, dissociation occurs, resulting in the separation of ions from an ionic crystal. Ionisation, on the other hand, is the process by which a neutral molecule dissolves in a solution and breaks into charged ions. The strength of ion-ion bonding and the extent of ion solvation determine the extent of ionisation.

The following are the most important and current concepts in acids and bases:

The Arrhenius Concept

Acids are substances that produce H+ ions when dissolved in water, while bases are substances that ionise in water to form OH– ions, according to the Arrhenius idea. 

HA→ H++A–  (Acid) 

BOH→B++OH–(Base) 

Acid-base reactions, according to Arrhenius, are characterised by acids dissociate in aqueous solution to form hydrogen ions (H+) and bases dissociation in aqueous solution to form hydroxide (OH–) ions.

The Arrhenius Concept’s Limitations

1.To act correctly, acids and bases require the presence of water. When HCl is dry, it cannot be employed as an acid. Only water, and no other solvent, forms an acid when it combines with HCl.

2.The method fails to explain why compounds in non-aqueous solvents are acidic or basic.

3.Although reactions involving salt formation can occur in the absence of a solvent, the neutralisation process is only plausible for aqueous-solution reactions.

4.Some salts, such as AlCl3, have an acidic characteristic in aqueous solution that is unknown.

5.A lengthy and convoluted explanation is required to clarify the basic nature of NH3.

Bronsted-Lowry Theory

In 1923, Bronsted and Lowry developed a more comprehensive concept of acids and bases. According to them, an acid is any hydrogen-containing material (molecule, anion, or cation) that may give a proton to another substance and a base is any hydrogen-containing material (molecule, anion, or cation) that can accept a proton from another substance. Any material (molecule, cation, or anion) that can accept a proton from another substance is referred to as a base. Acids, on the other hand, are proton donors, while bases are proton acceptors. 

Consider a reaction in which acids conjugate acid-base pairs.

Acid1 + Base2 →Acid2 +Base1 

 H2O + HCl→ H3O+ + Cl– 

In this process, HCl gives a proton to H2O, converting it to an acid. Water, on the other hand, receives a proton from HCl and hence is a base. In the reverse reaction, H3O+ ions transfer a proton to the Cl– ion, which, at equilibrium, occurs at the same rate as the forward reaction, turning  H3O+ into an acid. Because it receives a proton from the  H3O+ ion, Cl– ion is a basic.

Conjugate acid-base pairs are acid-base pairs in which the reaction components can be formed from each other by gaining or losing protons.

Bronsted Lowry’s Concept’s Limitations

1.Bronsted Lowry was unable to explain the reaction that took place in non-protonic solvents such as COCl3, SO2, N2O4, and others.

2.It can’t explain reactions between acidic oxides like etc. and basic oxides like etc., which can happen even when there’s no solvent present, e.g. (No proton transfer)

3.Despite the fact that substances like BF3 , AlCl3, and others lack hydrogen and hence are unable to contribute a proton, they still behave as acids.

Conclusion

We conclude that Acids and bases are used in a variety of applications in today’s world, not just in scientific laboratories. Acids and bases have a role in our daily lives, from food digestion to the medications we take, as well as the cleaning products we use.