BACKGROUND: Liquids of different densities will form layers when mixed together in a container. If the liquids are miscible, they may blend together to form a single layer. In order to get the greatest number of layers, it will be necessary to add the liquids to the container in the correct sequence. In this experiment you will mix together three different liquids in a test tube to form as many layers as possible.
PROBLEM: The three liquids you will use are water with yellow food coloring, methanol with blue coloring, and 1.0M sugar water with red coloring. Use beral pipets to slowly add the liquids to a test tube. Determine which liquid is the most dense, and which is the least dense. How many extra layers can be made by mixing the solutions together in various proportions? Be sure to include detailed descriptions of how the solutions were mixed and all observations of how they combined.
TEACHER NOTES: The food coloring is added to help see to what degree the various solutions mix. Make 1.0M sugar (sucrose) water by dissolving 342 grams of table sugar per liter of solution. The density of the sugar water can be modified by adding the colored water to it in different proportions. Other alcohols, such as ethanol or 2-propanol, can be substituted for the methanol. The sequence of adding the liquids should be from the most to least dense, starting with the sugar solution(s), then pure water, then the methanol. Water and methanol are miscible, if the mixture is stirred. However, if the two are slowly combined, an interface layer will form between them. With careful layering, eight or more layers can be easily achieved.
An alternative type of experiment is designed to challenge the student and force them to be creative in their approach to solve a specific problem. Instructionless lab experiments provide only enough information so that the student knows what needs to be discovered in the lab, but not all of details about how to do it. The student must decide which physical and chemical characteristics can be used to evaluate outcomes, what measurements and calculations are needed, and method of lab analysis would be best suited to solve the problem. In some cases, it may be necessary to provide a specific procedure or apparatus set-up to be used in an experiment. This information can be provided without detracting from the planning and thinking required by the student.