Notes of pH class 10

What is pH?

-A scale developed to measure the concentration of hydrogen ion in a solution is known as pH scale where p in pH implies ‘potenz’ in German.

-this scale is developed by Sorensen.

-pH is defined as the negative logarithm of H+ ion concentration. Hence the meaning of the name pH is justified as the power of hydrogen.

pH = -log [H+]

Another definition of pH

-pH of a solution is inversely proportional to the hydrogen ion concentration.

-A pH scale is a tool for measuring acids and bases. The scale ranges from 0-14:

-Solutions having a value of pH ranging 0 to 7 on pH scale are termed as acidic and for the value of pH ranging 7 to 14 on pH scale are known as basic solutions.

-Solutions having the value of pH equal to 7 on pH scale are known as neutral solutions. --The strength of acids and bases depends on the number of H+ and OH– ions produced. Acids furnishing more number of H+ ions are known to be strong acids and vice versa

.Limitations of pH Scale

pH value of a solution does not instantaneously give us an idea of the relative strength of the solution.

pH is zero for 1N solution of strong acid. 

pH is negative for concentrations 2N, 3N, ION of strong acids.

At higher concentrations, in place of pH Hammett acidity functions are used.

Importance of pH

1.Only a narrow range of pH change can be sustained by a living organism, any further change in pH can make the living difficult. For example: in the case of acid rain, the pH of water is less than 7. As it flows into a river, it lowers the pH of river water which makes the survival of aquatic life difficult.

2.We know that our stomach contains hydrochloric acid which helps in the digestion of food. When the stomach produces too much of hydrochloric acid during indigestion, we feel a lot of pain and irritation. Hence, we generally use antacids or a mild base which increases the pH of the acidic stomach and thus decreases the pain.milk of magnesia has been used in all the antacids because it is basic in nature 

3.Bacteria present in our mouth sometimes lower the pH of our mouth by producing acids through degradation of the food particle. Hence, we are instructed to clean our mouths with toothpaste (which are generally basic) to prevent their decay by maintaining the pH.

4.We experience a lot of pain in case of bee-sting as the bee injects the methanoic acid through its sting. Hence, we are generally advised to apply baking soda or other mild bases on the surface as it helps in maintaining the pH of the surface.