2. pH change as the cause of tooth decay:
When we eat food containing sugar, then the bacteria present in our mouth break down the sugar to form acids such as lactic acid.
Thus, acid is formed in the mouth after a sugary food has been eaten. This acid lowers the pH in the mouth making it acidic. Tooth decay starts when the pH of acid formed in the mouth falls below 5.5.
This is because then the acid becomes strong enough to attack the enamel of our teeth and corrode it. This sets in tooth decay.
The best way to prevent tooth decay is to clean the mouth thoroughly after eating food by rinsing it with lots of clean water.
Many tooth pastes contain bases to neutralise the. Mouth acid. The pH of tooth paste is about 8.0. Therefore, using the tooth paste, which is generally basic, for cleaning the tooth can neutralise the excess acid in mouth and prevent tooth decay.
3. Soil pH and plant growth:
Most of the plants grow best when the pH of the soil is close to 7. If the soil is too acidic or too basic the plants grow badly or do not grow at all. The soil may be acidic or basic naturally. The soil pH is also affected by the use of chemical fertilizers in the fields.
Most often the soil in the Fields is too acidic. If the soil is too acidic, (having low pH), then it is treated with materials like quick lime (.calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate). If the soil is too alkaline then its basicity is reduced by adding decaying organic matter which is acidic.
4. pH range and survival of animals:
Our body works well within a narrow pH range of 7.0 to 7.8. If due to some reason, this pH range gets disturbed in the body of a person, then many ailments can occur. The aquatic animals (like fish) can survive in river water within a narrow range of pH.
When the pH of rain water is about 5.6, it is called acid rain. Too much acid rain can lower the pH of river water to such an extent (and make it so acidic) that the survival of aquatic animals becomes difficult. The high acidity of river water can even kill the aquatic animals (like fish).
Acids are also present on other planets. For example, the atmosphere of planet Venus is made up of thick white and yellowish clouds of sulphuric acid. Hence, life cannot exist on the planet Venus.