This SIR is designed to support an interactive drill on the meanings of polarity, current and electron flow, oxidation, reduction, anode, cathode, and the directions of electrode and net reactions. These are all interrelated, and if you know the direction of one you can infer the directions of all the others. There are four options.
The first is a generalized electric circuit, whose unknown polarity has been set by the computer. By clicking on the various question marks you may reveal the polarity of source and load, and the directions of current flow, electron flow, and the meter reading (positive or negative).
The key to this, and all of the other circuits in this SIR, is to decide which item is the source. A DC source forces conventional (positive) current out of its positive terminal, and negative electrons out of the negative one. A most effective use of this and the other displays, is to reveal any one of the items, and ask the class to use Coulomb's law and the definition of polarity to predict each of the others before it is uncovered.
The remaining three displays extend these circuit ideas to electrochemical cells.
Electrolytic Cell
The load is a chromium plating cell. New directional processes hidden behind question marks are the weight of each electrode, the location of oxidation/reduction, anode/cathode, the electrode reactions, and the directions of ion migration. An effective use of this display is to begin by clicking on one of the items that originally says This gets ? and ask students to infer the directions of the other processes.
Reversible Cell
This is a Cr-Cd cell, of low potential, with a salt bridge, which may be driven either way by an external battery. The problems are the same as for the electrolytic cell; the point is that the cell is reversible.
Voltaic Cell
This allows you to construct a great number of voltaic cells from a selection of seven metal - metal ion electrodes. A voltaic cell is itself the source, and drives the circuit. There is a meter in the circuit, whose polarity is a new unknown. It’s interesting to see which definitions are the same as for the other cells. You can show why, in an electrolytic cell, the anode is positive and the cathode negative, while, in a voltaic cell, these polarities are reversed.
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Updated July 24, 2000