Chapter 3

### LEARNING OBJECTIVES

After completing this chapter, the reader should be able to:

• ► Define and classify liquid systems on the basis of their physical properties.

• ► List the identification terms, symbols, and definitions of common concentration expressions.

• ► Clearly understand each concentration expression.

• ► Solve problems by utilizing concentration expressions and convert from one concentration unit to another.

• ► Define and demonstrate an understanding of the colligative properties of nonelectrolyte and electrolyte solutions.

• ► Calculate the molecular weight of a solute from any of the colligative properties.

• ► Recognize the significance of Liso and ΔTf.

• ► Calculate osmolarity from concentration and vice versa.

• ► Show familiarity with the physiologic implications of colligative properties.

• ► Define an isotonic solution.

• ► Perform the calculations for preparing an isotonic solution.

• ► Use the appropriate tables to find freezing point depression values of solutions, sodium chloride equivalent values, and Sprowls' values.

### GENERAL CONSIDERATIONS

A solution is defined as a chemically and physically homogeneous mixture of two or more substances. Homogeneous is a term used to imply that a mixture is uniform; that is, all the parts are identical. When subjected to routine chemical and physical analysis, the parts test the same. A binary solution is a mixture of only two components. These two components are called the solute and the solvent. For a solution of a solid material in a liquid such as water, the solute is the solid component and the solvent is the liquid component—water in the case of most pharmaceutical applications. The possibilities for a solute and solvent mixture as a solution for all states of matter are 3 × 3 = 9, as shown here:

Solute Solvent Example
Gas Gas Air
Liquid Gas Fog
Solid Gas Iodine vapor in air
Gas Liquid Carbonated water
Liquid Liquid Alcohol in water
Solid Liquid Aqueous sodium chloride solution
Liquid Solid Mineral oil in paraffin
Solid Solid Gold-silver mixture, mixture of alums

Pharmaceutical solutions are mostly solids dissolved in a liquid, which is usually water or water combined with other liquids. They may be named for their use in the patient as outlined here:

Classification Characteristics
Oral solutions (elixir, syrup) Taken by mouth, inactives for flavor and viscosity, water usual solvent
Topical solutions Application to skin or mucous membranes, aqueous or alcoholic
Otic solutions (aural) For the ear; usually not aqueous; glycerin, propylene glycol, and polyethylene glycol
Ophthalmic solutions For use in the eye, inactives for viscosity, free of particulates, isotonic, sterile
Parenteral solutions For injection IV, IM, or SQ; few if any inactives; rigid standards for sterility; free of particulates; free of pyrogens; isotonic; immediate effect

The advantages of solutions as a ...

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