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CBSE Class 7 Chemistry Notes- Chapter 2 Acids, Base and Salts

                                           CHAPTER 2 ACIDS, BASES AND SALTS
Acid comes from the Latin word ‘acere’ which means ‘sour’. Acids taste sour. Some naturally occurring acids are:
Acetic acid- found in vinegar
Formic acid- found in ant’s sting
Citric acid- found in citrus fruits like lemon, orange, etc.
Lactic acid- found in curd
Tartaric acid- found in tamarind
Bases are bitter in taste. Their solution in water feels soapy. Some bases are:
Calcium Hydroxide- found in lime water
Ammonium Hydroxide- found in window cleaners
Sodium hydroxide- found in soap
The substances which are neither acidic, nor basic are called neutral substances.
There are certain types of substances which can test if a substance is acidic or basic. Such substances are called indicators.
Some common indicators are litmus, China rose, etc.
 LITMUS: A litmus paper is available in two colours- red and blue. Red litmus paper turns blue when dipped in a base and blue litmus paper turns red when it is dipped in an acid. When the litmus paper does not change colour, the solution is neutral.
When acid and base are mixed, they neutralize the effect of each other. This process is called neutralization. Neutralization results in salt formation and gives out heat.
                                          Acid + Base  Salt + Water + Heat
Neutralization in everyday life:

  • Indigestion: When our stomach contains too much acid, we take an antacid which contains a base and therefore neutralizes the effect of acid.
  • Ant sting: Ant sting injects acidic liquid into the skin. Rubbing moist baking soda neutralizes its effect.
  • Factory wastes: Factory wastes are primarily acidic and are therefore treated with a base.

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