SCH4C                     Lab #18 - Oxides of Metals and Non-Metals

Introduction: An electrochemical cell is constructed from two-half cells.  One half cell contains both the oxidized and reduced form of the oxidizing agent.  The other half-cell contains the corresponding forms of the reducing agent.  The half-cells are connected by means of a salt bridge or a porous container filled with an inert material through which ions can pass.  A wire completes the external circuit through which electrons can flow.  The cell voltage is calculated using 1.0 M solutions.  In this experiment, you will construct several cells to determine their Eo or electromotive force.

Problem:  Construct and then compare several electrochemical cells for their Eo force.

Apparatus:   safety goggles, test tubes, 100 mL beakers 250 mL beakers bunsen burner, u-tube, steel wool, galvanometer or voltmeter

Materials: Strips of metals, Cu, Zn, Pb and Mg and others. 1.0 M solutions of each of the above metals in their nitrate form.  Concentrated NH3 solution.  1.0 M NaCl solution, potassium nitrate.

Safety Issues:  Concentrated ammonia solution is very irritating to the eyes.  Wear safety goggles and avoid inhaling the vapour.  Lead compounds are poisonous.  Avoid spills and dispose of these materials properly in the hazardous waste containers.

Procedure: 1.  After reading through this procedure, create a data table to record your results.  Make sure that you cover all possible combinations of electrodes. 2. Clean the metal electrode with sandpaper or steel wool, and set up the apparatus as shown above. 3. Record the voltage of the cell.  If the needle shows a negative deflection in the reading, reverse the connections at the terminals.

Concluding Questions 1. Write balanced equations for each of the spontaneous cell reactions. 2. From a handbook of chemistry, look up the reduction potential of each of the half cells used in your experiment.   Calculate the Eo from these handbook potentials and compare them to your actual experimental results. 3. List some of the possible sources of error.