Strength of Acid Or Base Solutions

Strength of Acid Or Base Solutions

A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. The p in pH stands for ‘potenz’ in German, meaning power.

At 25 degree Celsius,

pH =7

Neutral Solution

H3O+ = OH 


Basic Solution

H3O+ < OH –


Acidic Solution

H3O+ > OH –


 Universal Indicator-

The Universal Indicator is a mixture of many different indicators (or dyes) that gives different colours at different pH values of the entire pH scale.

Importance of pH:

  • Human body works at a pH of about 7.4.
  • Our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach. During indigestion the stomach produces too much acid and this causes pain and irritation. To get rid of this pain, people use bases called antacids. These antacids neutralize the excess acid. Magnesium hydroxide (Milk of magnesia), a mild base, is often used for this purpose.
  • Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium hydroxyapatite (a crystalline form of calcium phosphate) is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.