Overview: Importance of pH in Everyday Life
In Class 10 Science, understanding the role of pH is crucial as it dictates many biological and chemical processes around us. Living organisms, including humans, can only survive within a narrow range of pH change. This topic explores how acidity and alkalinity affect our health, environment, and agriculture.
1. pH in the Digestive System
Our stomach produces Hydrochloric acid (HCl) to help in the digestion of food without harming the stomach lining. However, during indigestion, the stomach produces too much acid, which causes pain and irritation. To correct this, we use bases called Antacids (like Milk of Magnesia or Magnesium Hydroxide) which neutralize the excess acid.
2. pH Change as the Cause of 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. The best way to prevent this is to clean the mouth after eating food. Using toothpaste, which is generally basic, can neutralize the excess acid and prevent tooth decay.
3. Plants and Animals are pH Sensitive
- Soil pH: Plants require a specific pH range for their healthy growth. If the soil is too acidic (low pH), farmers treat it with materials like quick lime (calcium oxide) or slaked lime (calcium hydroxide).
- Acid Rain: When the pH of rain water is less than 5.6, it is called acid rain. When this flows into rivers, it lowers the pH of river water, making survival of aquatic life difficult.
4. Self-Defence by Animals and Plants
| Source | Acid/Chemical | Remedy |
|---|---|---|
| Bee Sting | Methanoic Acid | Mild base (Baking soda) |
| Nettle Leaf Sting | Methanoic Acid | Dock plant leaf (Basic nature) |
| Wasp Sting | Alkaline liquid | Mild acid (Vinegar) |
Quick Revision Points
- Human body pH range: 7.0 to 7.8.
- Stomach Acid: Hydrochloric acid helps digestion.
- Antacids: Bases used to treat acidity.
- Tooth Enamel: Made of calcium hydroxyapatite (hardest substance in body), corrodes at pH < 5.5.
- Nettle Sting: Inject methanoic acid causing burning pain.
Practice Questions
- Why is toothpaste used to clean teeth? (It is basic and neutralizes mouth acid).
- What is the chemical name of the acid present in an ant sting? (Methanoic acid).
- Name a mild base used for relief from bee stings. (Sodium hydrogen carbonate / Baking soda).
- At what pH does acid rain become harmful to aquatic life? (Less than 5.6).
- How can acidic soil be treated for better agriculture? (By adding bases like Chalk or Lime).
