More active metals give up electrons to less active metals. If
metals of different activities are placed in an electrolyte,
electrons will be transferred from the more active metal to the
less active metal. If a circuit of wires connects the two metals,
the electrons will flow through these wires and can do work. This
is how an electrochemical cell works.
An electrochemical cell uses chemical changes to produce electricity. If several electrochemical cells are combined, they are called a battery of electrochemical cells, or just a battery.
When an electrochemical cell uses a liquid as an electrolyte, it is
called a wet cell. If the electrochemical cell uses a paste as an
electrolyte, it is called a dry cell. A automobile battery is an
example of a battery of wet cells. A flashlight battery is an
example of a battery of dry cells.
The places where electrons leave or return to the
electrochemical cell are called the electrodes. Dry cell batteries
commonly use zinc and carbon as electrodes. Electrodes are
conductors which carry electrons into or out of a cell. The zinc
is in the form of a can. The can holds the electrolyte paste,
which has a carbon rod in the center. The electrolyte in the paste
of most dry cells is potassium hydroxide. Since potassium
hydroxide is a base (an alkaline substance), such cells are known
as alkaline batteries. However, acids can also be used as
electrolytes for dry cells.
In the dry cell, the zinc gives up electrons which enter the
paste electrolyte. The electrons then leave the dry cell through
the bottom of the can. The bottom of the can is commonly called
the negative terminal or the cathode. The electrons then flow
through a circuit and do work. The electrons return to the dry
cell by way of the positive terminal (anode) and enter the carbon
rod where they are stored for reuse. A dry cell can produce a
maximum of 1.5 volts of electricity. A six volt flashlight battery
is composed of four dry cells. Most dry cells are not
rechargeable. However, some are. One type that is rechargeable is
the nickel cadmium battery or NiCad battery.
The most common type of wet cell battery is the automobile
battery. This battery of wet cells uses the metals lead and lead
dioxide. The electrolyte is sulfuric acid mixed with water. The
lead gives up electrons to the lead dioxide. The electrons leave
the battery by way of the negative terminal (cathode), go through
the circuits of the car to do work, and return by way of the
positive terminal (anode). Each wet cell produces a maximum of two
volts of electricity. Since the typical car battery is a 12 volt
battery, such a battery is composed of six wet cells.
A car battery is recharged by the car's generator or alternator.
The generator or alternator generates a an electric current that
flows in the opposite direction of the flow of electrons in the
battery. This reverses the flow of electrons and places electrons
back on the lead. Such a battery can be recharged for years before
it wears out.
The car battery primarily produces electric current only to run
the car's starter. Once the car engine is running the alternator
or generator takes over and supplies the electric current to run
all the features of a car which require electric current. The only
time the battery supplies all of this electric current is when
these features are on and the car's engine is not running, or if
the generator or alternator is not functioning.
Another chemical source of electricity is the fuel cell. The
fuel cell differs from wet and dry cells in that some of the
materials that react are supplied from outside of the cell. In a
fuel cell, hydrogen and oxygen are supplied from outside of the
cell. At one electrode, hydrogen is oxidized, at the other oxygen
is reduced. Therefore, there is an electron flow from the hydrogen
to the oxygen. Water is the by-product of this chemical reaction.
The draw back to the fuel cell is that it produces small amounts of
electricity. In addition, hydrogen gas is very explosive and
dangerous to transport and use. Oxygen gas also has certain
hazards associated with it, especially that of fire.
Electric current can be used to breakdown many compounds. The
breakdown of any compound by the use of electric current is called
electrolysis. For example, bauxite is a compound containing both
aluminum and oxygen. Electrolysis is used to separate the aluminum
from the oxygen, so that aluminum can be made into useful
materials. An electric current is also used to separate water into
hydrogen gas and oxygen gas.
Electric current can also be used to deposit a metal on a
conducting metal. This technique is called electroplating.
Electroplating is used to plate cheaper metals with metals which
are resistant to corrosion such as: gold, silver, nickel and
In electroplating, a battery supplies electrons to the cheaper
metal which is to be plated. The metal which is to be plated on to
the cheaper metal is in a salt solution which contains positive
ions. These positive ions are attracted to the negatively charged
electrons causing this metal to bind to the cheaper metal and plate
it. Much jewelry is gold or silver plated. Nails are plated with
zinc to galvanize them. Screws and door knobs are often plated
with brass (an alloy of copper and zinc). Automobile bumpers are
something plated with chromium.