Reducing Heavy Metal Waste in Potentiometric Exercises in the General Chemistry Laboratory

Potentiometric laboratory exercises in general chemistry are known for producing a considerable amount of heavy metal waste. This manuscript describes strategies for reducing this waste and increasing the efficiency of operations by using miniaturized half-cells and Cl-(aq) based verification of the Nernst equation. Standard electrode half-cells and the reference electrode Ag(s)|AgCl(s)|Cl-(aq,3.0 M) are constructed in autopipettor tips. The standard half-cells are: Ag(s)|Ag+(aq), Cu(s)|Cu2+(aq), Pb(s)|Pb2+(aq), Zn(s)|Zn2+(aq) and Ag(s)|AgCl(s)|Cl-(aq). The inclusion of the Ag(s)|AgCl(s)|Cl-(aq) standard half-cell allows the determination of Ksp (AgCl(s)) from one cell measurement and from a combination of two cells. The cell used to investigate the effect of concentration on the cell potential is Ag(s)|AgCl(s)|Cl-(aq,3.0 M)||Cl-(aq, α M)|AgCl(s)|Ag(s). These strategies have reduced heavy metal waste twenty-fold.