11.1 The Dissolution Process

​Phase Transitions

Phase Diagrams

By the end of this section, you will be able to:

• Define and give examples of electrolytes

• Distinguish between the physical and chemical changes that accompany dissolution of ionic and covalent electrolytes

• Relate electrolyte strength to solute-solvent attractive forces

​For many gaseous solutes, the relation between solubility, C_g, and partial pressure, P_g, is a proportional one:

Cg=kPg

where k is a proportionality constant that depends on the identities of the gaseous solute and solvent, and on the solution temperature. This is a mathematical statement of Henry’s law: The quantity of an ideal gas that dissolves in a definite volume of liquid is directly proportional to the pressure of the gas.

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At 20 °C, the concentration of dissolved oxygen in water exposed to gaseous oxygen at a partial pressure of 101.3 kPa is 1.38 × 10⁻³ mol L⁻¹. Use Henry’s law to determine the solubility of oxygen when its partial pressure is 20.7 kPa, the approximate pressure of oxygen in earth’s atmosphere.

​Some liquids may be mixed in any proportions to yield solutions; in other words, they have infinite mutual solubility and are said to be miscible.

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Ethanol, sulfuric acid, and ethylene glycol (popular for use as antifreeze, pictured in Figure 11.13) are examples of liquids that are completely miscible with water.

​Separate layers are formed when immiscible liquids are poured into the same container. Gasoline, oil, benzene, carbon tetrachloride, some paints, and many other nonpolar liquids are immiscible with water.

​The dependence of solubility on temperature for a number of solids in water is shown by the solubility curves in Figure 11.16. Reviewing these data indicates a general trend of increasing solubility with temperature, although there are exceptions, as illustrated by the ionic compound cerium sulfate.