Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Our body works within a narrow pH range of to . Living organisms can survive only in a narrow range of pH change.
When the pH of rain water is less than , it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water, making the survival of aquatic life difficult.
Our stomach produces hydrochloric acid () that helps in the digestion of food without harming the stomach. During indigestion, the stomach produces too much acid, causing pain and irritation. To get rid of this, people use bases called antacids like Magnesium hydroxide (), also known as Milk of Magnesia.
Tooth decay starts when the pH of the mouth is lower than . Tooth enamel, made of calcium phosphate (), is the hardest substance in the body but gets corroded when the pH falls below due to acids produced by bacteria from food particles.
Bee-stings leave an acid (methanoic acid or ) which causes pain and irritation. Use of a mild base like baking soda () on the stung area gives relief.
Stinging hair of nettle leaves inject methanoic acid () causing burning pain. A traditional remedy is rubbing the area with the leaf of the dock plant, which is basic in nature.
📐Formulae
(Neutralization reaction in the digestive system)
(Action of antacid)
(Neutralizing a bee sting)
💡Examples
Problem 1:
A farmer finds that the soil of his field is too acidic ( is low). Suggest two substances he can add to the soil to neutralize it.
Solution:
The farmer can add Quicklime (Calcium Oxide, ) or Slaked lime (Calcium Hydroxide, ).
Explanation:
Plants require a specific pH range for healthy growth. If the soil is too acidic, basic substances like , , or Chalk () are used to neutralize the excess acidity.
Problem 2:
Why is it advised to brush your teeth after eating sugary food?
Solution:
Brushing with toothpaste (which is generally basic) neutralizes the excess acid produced by bacteria in the mouth.
Explanation:
Bacteria present in the mouth produce acids by the degradation of sugar and food particles remaining in the mouth after eating. If the pH drops below , the tooth enamel () begins to corrode. Toothpastes contain mild bases that react with the acid: .