In the early 1980s, a new idea fundamentally changed the way students work in the laboratory. That idea is microscale science. In microscale experiments, only the absolute minimum of materials is used. Typical solid chemical amounts are 0.5 g or less while liquid volumes range from 0.5 to 2 mL. The technique has become so popular that all science teachers' meetings now have workshops on the subject, and many educator publications, such as the Journal of Chemical Education, feature regular columns on microscale science.
The advantages of microscale experiments over traditional macroscale procedures are numerous. While the primary benefit of microscale experiments is that they require only small amounts of chemicals and produce little hazardous waste, there are several additional advantages. These experiments require less space to store the hazardous waste, save hazardous waste disposal charges, use less stockroom space, and decrease the risk to students in the laboratory of chemical exposure. Overall, microscale science experiments cost less, also.
Microscale science is not without its problems, however. It is difficult to adapt some traditional exercises to such a small scale. Microscale titration, distillation, and calorimetry experiments, for example, require unique apparatus and, therefore, new techniques. To be successful, students must learn how to handle minuscule amounts of material skillfully. Even a minor spill or mismeasurement can ruin a microscale experiment.
The recent proliferation of microscience laboratory manuals and low-cost microscale equipment have made microscale experiments accessible to most educators. The 3 microscale science experiments described here cover the general science topics of metathesis reactions, chromatography, and buffer solutions.
One of the first types of reactions a beginning science student learns is the metathesis or double-replacement reaction. Since only a small sample of each solution is necessary to observe the reaction products, usually a gas or precipitate, an experiment in metathesis reactions lends itself to microscale. Metathesis reactions can be used to illustrate the driving forces of reactions, to reinforce the solubility rules for inorganic solids, and to provide experience in writing molecular, ionic, and net ionic chemical equations. An experiment that involves mixing together many types of solutions also satisfies a student's inherent curiosity about how substances react.
Metathesis Reactions
Figure 1 A student performs double-
replacement reactions in a microplate.
Prepare 0.1 M concentrations of each of the following 7 solutions: calcium chloride, cupric sulfate, hydrochloric acid, sodium carbonate, sodium hydroxide, sodium phosphate, and zinc sulfate. (If you are unsure how to prepare these solutions, request Carolina's Solution Preparation Manual, B3-84-1201, available free.) These solutions are stable and have a long shelf life.
Before the experiment, ask students to write the molecular, ionic, and net ionic equations for every combination of 2 solutions. Students perform these reactions in a 24-well microplate by adding 1 mL each of 2 solutions to a well using 1 mL pipets. They record the formation of a precipitate or gas, or indicate if no reaction occurred. Ask students to identify the driving force for each reaction and explain any discrepancies between their observations and their predictions. If desired, use the hydrochloric acid and sodium carbonate solutions as unknowns.
Topics for further discussion include the chemistry of household products. Ask students to read the labels of common household chemicals, such as baking soda, vinegar, milk of magnesia, and others, and to determine the major ingredient in each. Write the molecular, ionic, and net ionic equations for the reactions of several pairs of ingredients. For example, sodium carbonate in baking soda reacts with acetic acid in vinegar to produce carbon dioxide, water, and sodium acetate. Be sure to warn students against mixing household cleaners, especially bleach, with one another because of the possible production of hazardous reaction products (Zumdahl 1993).
