Acid, Bases and Salts : pH Scale


pH Scale and Its Importance                                                                                                    

In our life , we always like fresh, tasty food. Have you ever think how our taste buds decide the good food or bad food. In simple words if i say How sour is the soup, you can decide whether u may like it or not. Similarly for many food items (for humans, for animals and even for plants) the acidity and basicity is parameter to consume that food or not. To measure this acidity in simple way, a scale is developed called pH scale. Higher pH means more sour , low pH means more bitter. 

But pH is not limited up to food items only, but it is useful to decide the products of many Chemical reactions. (Although, Food digestion is a big process involving many Chemical Reactions).

How pH is measured ? 

pH is defined as negative logarithm of H+ ion concentration.

pH = – log [H+]

  • The pH of a solution varies from 0 to 14 at 25ºC. 
  • Solutions having value of pH ranging 0 to 7 are termed as acidic solutions. More Close to 0 , more acidic the solution.
  • If the value of pH ranging 7 to 14 are known as basic solutions. More Close to 14 more basic solution.
  • Solutions having value of pH equal to 7 are known as neutral solutions.




pH of some of the acids and bases:

Acid/Base pH
Hydrochloric acid 0.1 – 1.0
Sulphuric acid 1.0 – 1.2
Phosphoric acid 1.3 -1.5
Acetic acid (Vineger) 2.9 – 3.0
Carbonic acid 3.8 – 4.0
Water 6.9 – 7.0
Ammonia 10.8 – 11.2
Sodium hydroxide 13 – 14


Importance of pH:

  • Our life sustain in narrow pH range close to 7.4 . Change in pH by 0.5 unit can make the survival of microorganisms, Enzymes difficult.
  • In case of acid rain, the pH of water is less than 7. As it flows into river, it lowers pH of river water which makes the survival of aquatic life difficult.
  • We know that our stomach contains hydrochloric acid which helps in the digestion of food. When 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.
  • Bacteria present in our mouth sometimes lower the pH of our mouth by producing acids through degradation of food particle. Hence, we are instructed to clean our mouth with toothpaste’s (which are generally basic) to prevent the decay by maintaining the pH.
  • 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.

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Metals and Non-Metals : Physical properties of Metals

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