Acid, Bases and Salts

You will learn in this chapter about:

*        Acids and bases.
*        Arrhenius theory.
*        Bronsted Lowry theory.
*        Lewis concept.
*        Properties of acids and bases.
*        Neutralization.
*        Basicity and acidity.
*        Strength of acids and bases.
*        Salts.
*        Classification of salts and some important salts.
*        Dissociation of water.
*        The concept of pH and pH scale.
*        The importance of pH.
*         Acid-base titration.
*        Standard solution.

9.1 ACIDS AND BASES:      

Introduction:

By the 15th century, chemists recognized a group of substances which had sour taste called acids (In Latin acidus meaning 'sour"). They also recognized another group of substances which had bitter taste and were used as good cleaning agents, called Bases.

In the 16th century, it was recognized that bases react with acids to 'destroy' or "neutrailize" them, forming an ionic compound called salt.

Nearly all fruits and foods contain acids. Lemons, oranges, grape-fruits, contain citric acid. All citrous fruits contain large amount of ascorbic acid (C6H8O6), or vitamin-C. Ascorbic acid also acts as an anti-oxidant. Apples contain maleic acid. The souring of milk produces lactic acid; butter on rancidity gives butyric acid. The extract of vinegar is acetic acid. Chemists prepare large quantities of important industrial acids. They are manufactured from minerals and Eire known as inorganic acids or more commonly mineral acids. These include hydrochloric acid (HCL), nitric acid (HNO3), sulphuric acid (H2SO4) and phosphoric acid (H3PO4). The most important acid is H2SO4. The consumption of (H2SO4) is an index to the state of civilization and prosperity of a country. The important acid for making explosives and fertilizers is (HNO3), and (HCL) is used as cleaning agent. It composes about 0.4% of gastric juice of our stomach and aids in digestion of food.

There are several substances found in almost every home, called bases, house hold ammonia (NH3+H2O solution) is common cleaning agent. Lye is commercial (NaOH) used for cleaning, sink-drains. Lime water is a solution of Ca(OH)2. Milk of magnesia (Mg (OH)2) is used as an antacid, laxative, and an antidote, when strong acids are swallowed.

Salts have a positive ion other than (H+) combined with a negative ion, other than (OH-). However, one must keep in mind that all the salts are not neutral, some behave like acids and others like bases. Thus many substance were grouped into one of the three classes, acids, bases, and salts.

 
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