Bases
- Bases are those chemical substances which have a bitter taste
- A base is a substance which dissolves in water to produce hydroxide ions (OH– ions) in solution.
Properties of Bases
- Bases have bitter taste
- Bases feel soapy to touch
- Bases turn red litmus to blue
- Bases conduct electricity in solution (They are electrolytes)
- Bases react with some metals to form hydrogen gas
- Bases react with acids to form salt and water
- Non-metal oxide + Base—- Salt + Water
Strength of acid and base solutions: pH scale
- In pure water, the concentrations of hydrogen ions and hydroxide ions are equal.
- Due to this, pure water is neither acidic nor basic, it is neutral.
- The universal indicator shows different colours at different concentrations of hydrogen ions in a solution
- A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed.
- The p in pH stands for ‘potenz’ in German, meaning power.
- On the pH scale we can measure pH generally from 0 (very acidic) to 14 (very alkaline).
- pH should be thought of simply as a number which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration, lower is the pH value
Importance of pH in everyday life
plants and animals pH sensitive
- Our body works within the pH range of 7.0 to 7.8.
- Living organisms can survive only in a narrow range of pH change. When pH of rain water is less than 5.6, it is called acid rain.
- When acid rain flows into the rivers, it lowers the pH of the river water.
- The survival of aquatic life in such rivers becomes difficult.
pH in our digestive system
- our stomach produces hydrochloric acid.
- It helps in the digestion of food without harming the stomach.
- During indigestion the stomach produces too much acid and this causes pain and irritation.
- To get rid of this pain, people use bases called antacids
- These antacids neutralise the excess acid. Magnesium hydroxide (Milk of magnesia), a mild base, is often used for this purpose
- pH change as the cause of tooth decay
- Tooth decay starts when the pH of the mouth is lower than 5.5.
- Tooth enamel, made up of calcium phosphate is the hardest substance in the body.
- It does not dissolve in water, but is corroded when the pH in the mouth is below 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 toothpastes, which are generally basic, for cleaning the teeth can neutralize the excess acid and prevent tooth decay
- Self Defense by Animals and Plants Through Chemical Warfare
- when a honey-bee stings a person, it injects an acidic liquid into the skin which causes immense pain and irritation
- baking soda solution on the stung area of the skin gives relief
- When a wasp stings, it injects an alkaline liquid into the skin.
- So, if a wasp stings a person, then rubbing a mild acid like vinegar on the stung area of the skin gives relief
- An ant’s sting injects methanoic acid into the skin of a person causing burning pain.
- Being acidic, an ant’s sting can be neutralized by rubbing a mild base like baking soda on the affected area of the skin.
- When a person happens to touch the leaves of a nettle plant accidentally, the stinging hair of nettle leaves inject methanoic acid into the skin of the person causing burning pain.
- The nettle sting, being acidic, can be neutralized by rubbing baking soda on the skin.
