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Unit 8: When Chemicals Meet Water—The Properties of Solutions

Section 1: Introduction

Solutions are mixtures of substances that are uniform throughout. They are found all around us, from the apple juice in our refrigerator to the fillings in our teeth, from the plasma of our blood to the air we are breathing. Solutions are fixtures of our daily lives and a critical subject in chemistry.

In this unit, we will define solutions and learn about their important characteristics and some of the techniques that chemists use to determine those properties. Next, we will examine the physical properties of solutions, with a special focus on the interaction of gases and liquids. Finally, we'll look at some methods of separating and purifying materials after they have been mixed together.

Food Coloring in Water

Figure 8-1. Food Coloring in Water

© Science Media Group.

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Food Coloring in Water

Figure 8-1. Food Coloring in Water

Yellow food coloring is added into a glass of water. Initially, we see that the dark yellow color is spreading out into the water. Eventually, it will form one distributed homogeneous solution that is all pale yellow and more dilute than the original food coloring.

Understanding the chemistry of solutions is important because most chemical reactions, both in the laboratory and in nature, take place in solutions. Because water is one of the most ubiquitous chemicals on Earth and is necessary for life, many important biological reactions involve aqueous solutions, which consist of substances dissolved in water. (Figure 8-1) In this case, the water is what we call the "solvent," and the substances dissolved in it are referred to as the "solutes." For example, water accounts for more than half of an average person's body weight, and a number of electrolytes (mineral salts) that regulate important physical functions are dissolved in it. If a person does not drink enough water and becomes dehydrated, his or her electrolyte concentrations can be thrown out of balance, which may cause symptoms such as dizziness, cramps, or irregular heartbeat.

Solutions chemistry is also central to many industrial processes. It can be a challenge to dissolve all of the reagents needed for a reaction into the same solution so they can react with one another in a timely manner. With an understanding of solutions, we can analyze problems such as how to blend medicines at appropriate concentrations for infants, children, and adults, or how to make industrial processes greener by making better solvents, recovering the solvents after the reaction is done, or eliminating solvents all together.

Glossary

Solutes

In a solution, the substances that are dissolved.

Solvent

In a solution, the substance in which the solute is dissolved.

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