You will learn in this chapter about:
* Acids and bases.
* Arrhenius theory.
* Bronsted Lowry theory.
* Lewis concept.
* Properties of acids and bases.
* Basicity and acidity.
* Strength of acids and bases.
* Classification of salts and some important
* Dissociation of water.
* The concept of pH and pH scale.
* The importance of pH.
* Acid-base titration.
* Standard solution.
9.1 ACIDS AND BASES:
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.