Acids and bases

Acids and bases

An acid is defined as a substance that gives off protons while a base is a substance that accepts protons as per the theory of Lowry and Bronsted. Thus, an acid is a proton (H⁺) donor and a base is a proton (H⁺) acceptor.

The general equation that represents the dissociation of an acid is as follows:

An acid dissociates to form proton and its conjugate base. On the other hand, the conjugate base combines with proton to form acid. The difference between an acid and its conjugate base is the presence or absence of a proton. In general, a strong acid has a weak conjugate base while a weak acid has a strong conjugate base. For instance, strong acid HCl has weak conjugate base Cl^–, weak acid HCN has a strong conjugate base CN^–

A few examples of acids and their corresponding conjugate bases are as follows.

Acids          Protons       Conjugate Bases

H₂O   ->      H⁺     +       OH^–  

HCl             ->      H⁺     +       Cl^–    

H₂CO₃         ->      H⁺     +       HCO3^–

CH₃COOH  ->      H⁺     +       CH3COO^‑

NH4⁺ ->      H⁺     +       NH₃

Acids and bases in biological systems

In general, acids are produced in the body as the end products of many metabolic reactions. These include the volatile acids like carbonic acid (most predominant, about 20,000 mEq/day) or non-volatile acids (about 80 mEq/day) such as lactic acid, sulphuric acid, phosphoric acid etc. Carbonic acid is formed from the metabolic product CO₂; lactic acid is produced in anaerobic metabolism; sulphuric acid is generated from proteins (sulfur containing amino acids); phosphoric acid is derived from organic phosphates (e.g. phospholipids). All these acids add up H⁺ ions to the blood.

The formation of bases in the body under normal circumstances is negligible. Some amount of bicarbonate is generated from carbondioxide. The ammonia produced from amino acids is converted to urea.