A typical household battery is an electrochemical (or galvanic) cell:  a cell that produces a flow of electrons, i.e. a current.  To accomplish this, one reagent must be oxidized and another must be reduced; the reagents must also be physically separated, forcing the electrons to flow through an external circuit to move from one reactant to the other.  Chemists define the electrode at which oxidation occurs as the anode, and that at which reduction occurs as the cathode.  
	This module simulates the construction and operation of electrochemical cells.  The standard two-compartment cell has two solid electrodes connected by a wire where the voltage of the cell can be measured.  In this simulation, each compartment may contain one of the seven redox couples (generally an oxidized species in solution and a reduced solid electrode). 
A porous disk allows ions to flow between compartments while keeping the two bulk solutions from mixing.  The NO3- in solution undergoes ion migration to offset charge buildup that would otherwise occur as electrons flowed. The concentrations of the species in each solution may be adjusted, and several different oxidation and reduction reactions are available.  The voltage is calculated and displayed after any change is made.

INSTRUCTIONS

1.  Select an anode reactant species by clicking on one of the
     seven Anode option buttons.
2.  Choose concentration of the solution species at the anode
     by adjusting the anode concentration scroll bar, which adjusts
     the concentration between 0.10 and 1.0 M.
3.  Select the cathode by clicking on one of the seven Cathode buttons.
4.  Choose the solution concentration species at the cathode by 
     adjusting the cathode concentration scroll bar.  This scroll bar 
     adjusts the concentration value between 0.10 and 1.0 M.
5.  As changes are made, the voltage of the cell is displayed in the 
     volt meter above the cell.