What is a solution?

Solutions

What is a solution?

Learning Target 3.3.1: I can explain the dynamic process by which a solution is formed when one or more solute dissolve in a solvent. I can calculate solution concentration in terms of molarity, percent concentration, and parts per million.

Solutions

Goal 3.3.1.a: I can define the terms solute, solvent, and solution.

Goal 3.3.1.b: I can identify a solvent and a solute in a given solution.

A solution is a special kind of homogeneous mixture that has something dissolved in something else. For example, tap water is a solution because it contains minerals, salts, and other chemicals in addition to water molecules.^[1] Conversely, distilled water is not considered a solution because all the of the chemicals and minerals have been removed, leaving only water molecules. Distilled water is said to be “pure”, because it contains only one type of compound, i.e. H20.

Every solution has two parts: a solute and a solvent. A solute is the substance that is being dissolved. A solvent is the substance that is dissolving something else. If we think about our tap water example, the solutes are the minerals and chemicals, and the solvent is the water. Another simple example of a solution is salt water. If we dissolve table salt in a glass of water, the salt is the solute, and the water is the solvent. See the picture below.

^[2]solute (salt) dissolving in solvent (water)

Most solutions that we will talk about are liquid solutions that have one or more gas or solid solutes dissolved in a liquid solvent. However, there are also solutions where a gas solute is dissolved in a gas solvent, and solid solutions that have one solid dissolved in another solid. See the table below.

Table 3.3.1 Types of Solutions^[3]

Concept check:

For each of the solutions given, identify the solute and the solvent. Give a brief explanation for each.

5. Kool-Aid

6. Sugar added to water

7. Carbonation in pop

8. 45.8 g of NaCl added to 540 mL of C2H5OH (ethanol).

Student misconception: Many students think that mixtures are solutions.

Explanation of misconception: As discussed above, solutions are a special kind of homogeneous mixture. Heterogeneous mixtures are not solutions. See the Classification of Matter map below.

Classification of Matter:

Do the lab, Lab # 2: Separation of a Mixture Procedure^[4]