Unit Solutions, Dilutions and Concentrations

Materials: Water, Finger nail polish remover (Acetone), table sugar, salt, cigarette filters, candle wax, butter, dish soap, cups, sharpie pens, napkins, and cooking oil.

Objective: The goal of this lesson is to familiarize 7^th Grade students with solutions and concentration of substances within solutions.

Background:

Solvent (definition) - A substance usually a liquid capable of dissolving another substance. There are different types of solvents and most are liquids. For instance, one great solvent is water. Water is capable of dissolving many substances and holding them in solution.

Solute (definition) - A substance dissolved in another substance, usually the component of a solution present in the lesser amount. One great example of a solute is salt in water. Notice that salt is not called a solute when it is not part of a solution. Once it becomes part of a solution it then becomes the solute.

Solution (definition) - a homogeneous mixture of two or more substances, which may be solids, liquids, gases, or a combination of these.

Precipitate (verb definition) - to be separated from a solution as a solid.

Precipitate (noun definition) - A product resulting from a process, event, or course of action

Together, the solvent and the solute make a solution. A solvent by itself is not called a solution.

Once a solid substance has been dissolved into solution, the solute may precipitate out of solution perhaps by reacting with another substance, or by changing the temperature of the solution or by changing the pressure under which the solution is held.

Procedure:

Present the materials to students and ask them if they were to make a solution out of these substances, then to identify which ones would be solvents and which ones might be solutes. Ask students to write down their predictions regarding their plan for making solutions.

Once students make their predictions about each of the solvents and solutes, allow them to explore their ideas. It may be best for the instructor to perform the requests of the students as they state their predictions.

The acetone and the water are solvents.

The other substances can be considered solutes once they are dissolved in the solvent to make a solution.

The cigarette filters should dissolve in the acetone but not in the water.

The Butter will dissolve in water only if the water has soap in it.

The acetone will dissolve a sharpie pen mark

Some other common solvents that you would find in a scientific laboratory include ethanol and methanol.

Sometimes these solvents are used to allow a certain substance to be dissolved in water. For instance some substances that are not soluble in water can be dissolved in water by first dissolving it in another solvent and then mixing that solution with water.

To illustrate this, first show students that acetone and water can mix together

Try to dissolve some of the substances that are insoluble in one solvent by first dissolving it in the other solvent and then mixing the solution and the solvent together. For example, dissolve the cigarette filter in the acetone. The resulting solution should be a white milky color. Then try to mix this white milky solution with water. Does everything stay in solution or does the solute precipitate out of solution?