8.1 Formation of Solutions

Reading Focus

Key Concepts

• What are three processes that can occur when substances dissolve?

• What are some properties of a solution that differ from those of its solvent and solutes?

• What happens to energy when a solution forms?

• What factors affect the rate of dissolving?

Vocabulary

• solute

• solvent

• dissociation

• dispersion

• ionization

Reading Strategy

Comparing and Contrasting Copy the Venn diagram below. Contrast dissociation and ionization by listing the ways they differ.

d

Figure 1 If divers surface too quickly from great depths, the nitrogen that has dissolved in their blood and other tissues bubbles out of solution. These bubbles can become trapped in joints and cause great pain, a condition called “the bends.”

Scuba divers, like the one in Figure 1, are able to breathe underwater with the aid of a tank containing compressed air. Like the air you breathe at sea level, the air inside the tank contains about 78 percent nitrogen. As a scuba diver descends to greater depths, the pressure of the air in the diver's lungs increases. At a depth of 10 meters, the air in the diver's lungs is already twice the pressure of the air at sea level.

The human body consists mainly of water. When gases come in contact with water, they dissolve in the water to form a solution. The deeper a scuba diver goes, the greater is the air pressure in her lungs, and the more nitrogen dissolves in the blood and tissues of her body. The idea of a gas dissolving may seem strange to you. When you hear the word dissolve, you probably think of a solid dissolving in a liquid, such as sugar added to tea. However, any states of matter—solid, liquid, and gas—can become part of a solution. For a solution to form, one substance must dissolve in another.