Bases and Properties, pH in Everyday Life

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.