Page 19 - Pharmaceutical analytical chemistry |

Density and specific gravity of solutions
Density and specific gravity are terms often encountered in the
analytical literature. The density of a substance is its mass per unit
volume, whereas its specific gravity is the ratio of its mass to the
mass of an equal volume of water at 4°C. Density has units of
kilograms per liter or grams per milliliter in the metric system while
specific gravity is dimensionless. The two terms are used
interchangeably.

ACID – BASE EQUILIBRIA

 Electrolyte solutions

Electrolytes are substances (acids, bases, or salts) that form ions when
dissolved in water and thus produce solutions that conduct electricity.
The amount of ionization is dependent on the strength of the electrolyte.
Strong electrolytes ionize essentially completely in a solvent; where as
weak electrolytes ionize only partially.

 Acid-base theories

1) Arrhenius theory
An acid ionizes in H2O to give hydronium ion.

HA + H2O ↔ H3O+ + A-
A base ionizes in H2O to give hydroxyl ion.

B + H2O ↔ BH+ + OH-
This theory did not discuss the role of solvent in the ionization process.

2) Brönsted-Lowry theory
According to the Brönsted-Lowry theory, an acid is a proton donor and a
base is a proton acceptor. In order for a species to behave as an acid, a
proton acceptor (or base) must be present. The reverse is also true.

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