- Plants cannot grow in highly alkaline or highly acidic soils. Most food crops grow best at a pH of 7-7.8.The growth of plants suffers when the pH value is outside this range.
- If the soil is too acidic then its pH can be raised by adding lime (or slaked lime) which neutralises 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 neutralise the excess alkali present in the soil.
The pH scale plays a critical role in the human body. Different parts of the human body have different pH.
The mouth has a slightly alkaline pH while the stomach has a very acidic pH. The skin has a slightly acidic pH, and the pH in the Vagina is again very acidic.
- pH in our digestive system
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. A mild base called Magnesium hydroxide (Milk of magnesia) is an antacid which neutralises the excess acid.
- pH change as the cause of tooth decay
The saliva in the oral cavity makes the pH of the mouth alkaline.The alkaline pH facilitates the action of salivary enzymes. It also prevents tooth decay.Tooth decay starts when the pH of the mouth is lower than 5.5.Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating.
- pH of skin and Vagina.
The acidic pH of the skin and vagina prevent colonisation by bacteria, thus serving as a natural defence against infection.
- When pH of rainwater is less than 5.6, it is called acid rain.