Difference Between Voltaic Cells And Wet Cell
The flow of electrons, or electricity, in oxidation-reduction reactions presents an interesting possibility. What if the flow of electricity could be harnessed and used in a practical way? This is what happens whenever we use a car battery to power headlights, or a dry-cell battery to power a handheld calculator, flashlight, or other portable device. The batteries supply electricity through oxidation-reduction, or “electron-transfer,” reactions.
Batteries of all sorts are voltaic cells. A voltaic cell is a device in which chemical energy is changed into electric energy. Let us follow what happens when we build our own simple voltaic cell.
Wet-Cell, or Secondary, Batteries
The simple battery we are about to describe is an example of a wet cell, perhaps more commonly known as a storage battery or secondary battery.
First, we place an electrode made of zinc (Zn) into a beaker filled with a solution containing zinc ions (Zn2+). Next to it, we place a copper electrode in a beaker filled with a solution containing copper ions (Cu2+). Both solutions likewise contain negative sulfate ions (SO42−), but they will not be directly involved in our chemical reactions.
Next, we connect the two beakers with a glass tube that contains a solution of a third electrolyte such as potassium sulfate (K2SO4). The electrolyte ions in this salt bridge provide a way for electrons, or electrical current, to pass between the two solutions.
Finally, we connect the copper system and the zinc system by linking their electrodes with a metal wire. Immediately, an electron-transfer reaction occurs, and electricity begins flowing from the zinc electrode to the copper electrode.
The important effect is a continuous current of electricity passing through the wire that connects the two solutions. This electricity can be tapped to perform useful work such as powering lights or operating a device such as a calculator or a portable radio. The electric current will continue until the zinc electrode is used up. The zinc electrode can be recharged, or restored to its original condition, by applying an electric current from an outside source. This reverses the overall reaction.
The lead-acid battery used to start an automobile is another example of a wet cell. It is continuously recharged by a generator or alternator when the car engine is running.