Study Notes On Chemistry : pH Scale

Here we are providing the short notes on Biology which will be help to crack science part in may examinations like SSC, Railway and other competitive exams.


The p in pH stands for ‘potenz’ in German, meaning power.

  • The scale that measures the strength of an acid or a base is called the pH scale. This value lies between 0 and 14.
  • Higher the hydronium ion concentration, lower is the pH value.
  • The pH of a neutral solution is 7. Values less than 7 on the pH scale represent an acidic solution. As the pH value increases from 7 to 14, it represents an increase in OH– ion concentration in the solution, that is, increase in the strength of alkali.
  • Most food crops grow best at a PH of 7-7.8.If the soil is too acidic then its pH can be raised by adding lime (or slaked lime) which neutralizes the excess acid in the soil.Similarly, if the soil is too alkaline then its pH can be lowered by adding gypsum or some other substance which can neutralize the excess alkali present in the soil.
  • The medium in our stomach is highly acidic and has pH around 1.2. Our stomach produces hydrochloric acid which helps in digestion of food. Magnesium hydroxide (Milk of magnesia), a mild base, is an antacid which neutralises the excess acid.
  • Tooth decay starts when the pH of the mouth is lower than 5.5.
  • Acid Rain- When pH of rain water is less than 5.6, it is called acid rain.
  • Gastric juice – 1.2
  • Lemon Juice – 2.2
  • Pure water – 7.4
  • Milk of mgnesia – 10
  • Sodium hydroxide solution – 14
  • Note – The atmosphere of venus is made up of thick white and yellowish clouds of sulphuric acid.

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