Hold down the T key for 3 seconds to activate the audio accessibility mode, at which point you can click the K key to pause and resume audio. Useful for the Check Your Understanding and See Answers.
Lesson 1: A Model of Solutions
Part a: What is a Solution?
Part a: What is a Solution?
Part b:
Solubility and Structure
Part c:
The Dissolving Process
Part d:
Solubility, Temperature, and Pressure
Part e:
Dissociation of Ionic Compounds
Solutions Are Everywhere
In Chapter 2 of our Chemistry Tutorial, we discussed the distinction between pure substances and mixtures. In nature, mixtures are considerably more common than pure substances. And even in our daily lives, the consumer products that we encounter are more likely to be mixtures of two or more substances than they are to be pure substances.
One type of mixture is a solution. It is mixture in which its parts or components are intermingled in such a matter that you cannot distinguish between them. Solutions are everywhere. The air you breathe is a solution of several gases, predominantly nitrogen and oxygen gas. The water you drink is a solution of numerous minerals and salts, and on occasion, dissolved gases. The likelihood is hight that the food you eat, the clothes you wear, the products in your refrigerator and kitchen cabinets, the surfaces you walk on and sit on and sleep on, and just about everything else is a solution. Given their prevalence, a Chemistry Tutorial that focuses on the study of matter would not be complete without a discussion of solutions.
What is a Solution?
A solution is a homogeneous mixture of two or more substances. In referring to a solution as homogeneous, we mean uniformly distributed. The two (or more) parts are intermingled evenly. The air you breathe at head level is guaranteed to be identical to the air at the top and the bottom of the room since its parts are distributed uniformly.
A solution is a stable mixture. Provided temperature and pressure conditions are maintained, the parts of the solution will not separate and settle out. This makes a solution quite different than a heterogeneous mixture like oil and vinegar salad dressing. When the salad dressing is mixed, the oil and vinegar intermingle. But their intermingling is a temporary condition, and within time the oil and vinegar will once again settle out into their separate phases. A solution is not like that; the intermingling of its parts is not a temporary condition. It is a stable mixture; its parts will not settle out.
A solution consists of a solvent and at least one solute. These can be solids, liquids, or gases. While air is a mixture of several gases, tap water is a mixture of numerous solids and some gases dissolved in liquid water. A metal alloy, discussed in Lesson 3a of Chapter 11, is most often a mixture of two or more solids. Vinegar is a homogenous mixture of water and acetic acid. A soda is a mixture of water, flavorings, sweeteners, colorants, and dissolved carbon dioxide gas.
The solvent is generally regarded as the dissolving medium or the major component in the mixture. The solutes are the other components that are dispersed about the dissolving medium. Maintaining a stable solution requires that the solvent and the solute interact at the particle level through interparticle forces that hold them in place and ensure their stability. We will discuss the role of these interparticle forces in greater detail in Lesson 1b.
Aqueous Solutions
An aqueous solution is a solution in which water is the solvent. Partly because water is so abundantly available on Earth, and partly because it is such an effective solvent, aqueous solutions are the most common type of solution both inside and outside of the Chemistry classroom. Water is very effective at dissolving ionic compounds and polar covalent compounds. Even biological compounds like protein, enzymes, and B and C vitamins readily dissolve in water. Only nonpolar substances like oils, fats, gasoline, and other hydrocarbons are unable to dissolve in water.
Most of our studies of solutions in Chapter 13 will be focused on aqueous solutions. The particles that are dissolved in an aqueous solution can be atoms, molecules, or ions. As we continue through these lessons, we will learn why and how solutes dissolve, why and when the dissolved particles are ions, the factors that affect the amount of dissolved solute, and how to mathematically describe the amount of solute that is dissolved in water.
Before You Leave
- The Check Your Understanding section below include questions with answers and explanations. It provides a great chance to self-assess your understanding.
Check Your Understanding
Use the following questions to assess your understanding. Tap the Check Answer buttons when ready.
1. Describe the difference between a pure substance, a homogeneous mixture, and a heterogeneous mixture.
2. Consider the following descriptions of a sample of matter. Based on the description, is the sample (in
bold lettering) a solution or not?
- The bottle of high pulp orange juice has not been used for a while. Most of the pulp is located in a layer at the bottom of the bottle.
- A brass candlestick consists of 68% copper and 32% zinc.
- When picking up the can of paint at the paint store, the employee put the can in a machine that shook it vigorously. She then gave you three paint sticks and said "be sure to stir the paint vigorously before using it."
- You purchased a new brand of contact lens cleaner in a clear bottle and it appears to be a single substance; yet the label lists a variety of ingredients.
- The box of baking soda in the refrigerator boasts of consisting of pure sodium bicarbonate.
3. Water is sometimes referred to as a universal solvent. Does that mean that water dissolves everything?
4. Explain how you can tell the difference between the solute and the solvent for a solution.