Unknown Identification by Simple Stoichiometry This paper describes a brief, simple experiment hy which the student candetermine the identity "fa saluhle carbonate salr using one ~trlghtforwardreaction and gravimetnc analysis. Materials 150-mL beaker 6 M HC1 Bramthymal blue t h r e e decimal balance NaHC03, NazC03, KzCOa(Hz0)w Procedure Weight out about 0.500 g of unknown salt and place it in a previously weighed beaker. Dissolve the salt in several milliliters of distilled water and add 2 drops of Bromthymol blue indieator. Slowly add HC1 until the blue solution turns yellow. Carefully evaporate the solution to dryness, with low heat near the end to avoid loss of material from spatteling. Weigh the beaker and product when rmm temperature is reached. Each student is asked to balance the three potential reaction equations and determine the theoretical amount of chloride salt expected for each. The product from NaHC03 will be 69.6% of the starting weight; NazC03 will he 110%, and the potassium salt 90.3%. These figures are widely separated and should afford unambiguous identifications. Anhydrous &C03 gives a figure very close to that from NazC03 and should not be used. Bro. Thomas McCullough, CSC St. Edward's University Austin. Texas 78704
592
Journal of Chemical Education
