An acid is defined as a proton donor. This is because when dissolved in water it dissociates releasing a proton (H⁺) which combines with water molecules to form an acidic solution  [H₃O⁺] > [OH^–] on the other hand bases are defined as a substance present H3O⁺ hence reducing their concentration. A base is thus defined in simple terms as a proton acceptor and the solution formed after combining with H₃O⁺ is basic([H₃O⁺]<[OH-].some bases however accept the proton without dissociating. Acids and Bases can be classified as strong or weak acids or bases. The strength is measured by the ease with which they ionize when dissolved in water. A strong bases or acid ionize to a big extent and hence change the PH of the solution markedly. Examples of strong base and acid are sodium hydroxide a (NaOH) and hydrochloric acid (HCL) .sodium hydroxide  ionize almost completely in water raising the PH markedly as it contributes a large increase of hydroxyl ions in the solution  while HCL ionize substantially and contribute an increase in H⁺ hence lowering the PH greatly. On the other hand a weak base for instance ammonia accepts protons from the aqueous solution in which it’s dissolved to a small extent while a weak acid like acetic acid ionizes slightly in water and hence alter the PH just slightly. When an acid dissociates or donates a proton the product is the conjugate base of that acid while a base ionizes to form the conjugate acid of that base these are termed as acid/ base pairs.

Buffers are defined as solutions that resist PH airs. change .they are made up of a weak acid and its conjugate base and thus the weak base resists PH change when an acid (H⁺) is added while the weak acid resists PH change when a base (OH^–) is added. A good example of a buffer is a mixture of sodium acetate and acetic acid.

The strong base has been converted to a weak base CH₃COO ^– which will have very little effect on pH.

When acid like HCL is added it combines with the buffer to form a weak acid with little effect on PH as shown in the equation below.

CH₃COO^– +   H ⁺   →CH₃COOH

 On the other hand when a strong base like NaOH is added it combines with the buffer and the product is a weak base with little effect on the PH.

CH₃COOH +   OH^–   → CHCOO^–+ H₂O.

Physiological buffers

The most widely used buffer system in the body is a mixture of carbonic acid (H₂CO₃) and its conjugate base bicarbonate ion (HCO₃ ^–).