Acid base concepts know it easy

Acid – Base concepts

Arrhenius concept

Swedish chemist Svante Arrhenius published his theory of acids and bases in the year 1887

According to the Arrhenius concept ::

•   A substance is classified as an acid  if it produces Hydrogen ions(H+) or Hydronium (H3O+) ions in water(aqueous solution)

•   A substance is classified as a base if it produces Hydroxyl ions (OH-) in water

Bronsted-Lowry concept - ( Proton-donor-acceptor concept)

Independently proposed by Bronsted and Lowry in the year 1923

• An acid  is a substance (molecule or ion) that can donate a proton, i.e., a hydrogen ion, H+, to some other substance

 

• A base is a substance that can accept a proton from an acid

•  An acid is a proton donor (protogenic) and a base is a proton acceptor (protophilic)

• A conjugate acid-base pair is formed , which differs in only the protons between the reactant and the product

Example::

HCl + H2O ↔ H3O + Cl-

• HCl acts as an acid because it donates a proton to the water molecule.

• Water, on the other hand, behaves as a base by accepting a proton from the acid.

Lewis concept

This concept was proposed by G.N. Lewis in 1939

·         

•  An Lewis acid is a substance that accepts an  electron pair and will have vacant orbitals in them , they are electrophiles ,All cations are lewis acids , Any atom, ion, or molecule with an incomplete octet of electrons can act as an Lewis acid (e.g., BF3, AlF3).

• A Lewis base is a substance that can donate an electron pair and will have lone-pair of electrons in their orbitals , they are nucleophiles , an atom, ion, or molecule with a lone-pair of electrons can  be a Lewis base (e.g ., OH−, CN−)

Amphoterism / amphoteric substances

Substances that are  capable of acting as either an acid or a base are amphoteric , the phenomenon is called amphoterism

·         Water , Ammonia are important amphoteric substances