non electrolyte part1

Material substances can be mixed together to form a variety of pharmaceutical mixtures such as true solutions, colloidal dispersions, and coarse dispersions. A dispersion consists of at least two phases with one or more dispersed (internal) phases contained in a single continuous (external) phase. The term phase is defined as a distinct homogeneous part of a system sepa¬rated by definite boundaries from other parts of the system. A true solu¬tion is defined as a mixture of two or more components that form a homogeneous molecular dispersion, in other words, a one-phase system. In a true solution, the suspended parti¬cles completely dissolve and are not large enough to scatter light but are small enough to be evenly dispersed resulting in a homogeneous appearance. The diameter of particles in coarse dispersions is greater than ~500 nm (0.5 mm). Two common pharmaceutical coarse dispersions are emulsions (liquid-liquid dispersions) and suspensions (solid-liquid dis¬persions). A colloidal dispersion represents a system having a particle size intermediate between that of a true solution and a coarse dispersion, roughly 1 to 500 nm. A colloidal dis¬persion may be considered as a two-phase (heterogeneous) system under some circumstances. . However, it may also be considered as a one-phase system (homogeneous) under other circumstances. For example, liposomes or microspheres in an aqueous delivery vehicle are considered to be heterogeneous colloidal dispersions because they consist of distinct particles constituting a separate phase. On the other hand, a colloidal dispersion of acacia or sodium carboxy methylcellulose in water is homogeneous since it does not differ significantly from a solution of sucrose. Therefore, it may be considered . as a single-phase system or true solution. A solution composed of only two substances is known as a binary solution, and the components or constituents are referred to as the solvent and the solute. Commonly, the terms component and constituent are used interchangeably to represent the pure chemical sub­stances that make up a solution. The number of components has a definite significance in the phase rule. The constituent present in the greater amount in a binary