Answer the following question in detail:

1. With reference to PH scale,

I. i.Write formula of pH and pOH

ii Mention pH and concentration of H₃O ⁺ or OH^- in acidic, basic and neutral aqueous solutions.

iii Mention limitations of pH scale.

2. Explain the importance of pH in everyday life.

3. “The aqueous solution of the salt produced by neutralization of weak acid and strong base possesses basic nature, while an aqueous solution of salt produced by neutralization of a weak base and strong acid possesses acidic nature” – Explain.

1 i.pOH = -log₁₀[OH^-]

pH = -log₁₀[H₃O ⁺ ]

ii. 1.acidic solutions have hydronium ion concentration greater than 10^-7 M and hydroxide ion has a concentration of less than 10^-7 M. Thus the pH of the acidic solution is less than 7.

2. Basic solutions have hydroxide ion concentration greater than 10^-7 M and hydronium ion has a concentration of less than 10^-7 M. Thus the pH is greater than 7.

3. in a neutral solution, the concentration of hydronium ions is equal to that of hydroxide ions which is equal to 10^-7 M. thus the pH is 7.

iii. The limitations of the pH scale are as follows:

•pH scale is applicable to aqueous solutions only.

•pH scale is valid for aqueous solutions having concentration bless than 1 M because its range is 0 to 14.

2. the importance of pH in our daily life is as follows:

•Importance of pH for the existence of living beings:

The various reactions that occur inside living beings require a specific pH range of 7.0 to 7.8. the living beings are not able to survive large changes in pH.

•Importance of pH in digestive systems:

As the food enters the stomach, hydrochloric acid is secreted. This decreases the pH in the stomach. The pH in the stomach turns between 1 and 3. In the decreased pH, the enzyme pepsin becomes active and helps in the process of digestion.

•Importance of pH in stopping the decay of teeth:

When the pH on the inner side of our mouth is less than 5.5 then the tooth decay starts. To prevent the teeth from decaying we use basic toothpastes which neutralise the acid produced inside our mouth.

3. The aqueous solution of the salt produced by neutralization of weak acid and strong base possesses basic nature. This is because the salt produced undergoes hydrolyzes during which it combines with H ⁺ ions from water liberating free hydroxide ions.

For example: Sodium acetate is a salt made by the reaction between strong base NaOH and weak acetic acid.

It undergoes hydrolyzes as follows to liberate hydroxide ions:

An aqueous solution of salt produced by neutralization of a weak base and strong acid possesses acidic nature. This is because such salt undergoes hydrolyzes and produces hydronium ions.

For example ammonium nitrate is made from the reaction between strong acid nitric acid and weak base ammonium hydroxide.