Identification of ionic compounds may be accomplished by studying their physical and chemical properties. One of the first physical properties that students readily recognize is color. One of the first chemical properties used to teach students to predict the result of mixing compounds is their solubility in water to determine if a precipitate will be observed. In this experiment students are given eight solutions and must identify them using a physical property, color and by their reactivity to form precipitate as is commonly done in qualitative analysis experiments and is a common component of high school and undergraduate curricula. Very often compounds containing toxic cations such as Pb2+ and Ba2+ are used since the precipitates form quickly and sink to the bottom of a test tube. This experiment uses greener and less toxic copper, cobalt, and strontium solutions. In this experiment, 10 M solutions of cobalt(II) nitrate, cobalt(II) sulfate, copper(II) nitrate, copper(II) nitrate, sodium sulfate, sodium carbonate, sodium hydroxide, and strontium nitrate are provided to students labeled A-G. The students identify the unknowns by their color and reactivity with each other. Students are asked to predict whether a precipitate will form using a solubility table. Known solutions are available to the students to aid in the identification of their unknowns.
The link to the laboratory procedure includes a predictions grid and a report template.
Summary prepared March 2012 by Dr. James Goll, Edgewood College
Goll, J. Identifying chemical compounds in solution by physical and chemical properties, Department of Chemistry, Geoscience and Physics, Edgewood College, Madison, Wisconsin, 2012