Electrolysis - Part I
Electrolysis is a process by which electrical currents can be passed through solutions. Pure water is a non-conductor of electricity. But if a salt such as NaCl is dissolved in it, the solution will start conducting if two electrodes are placed in it along with a battery that provides the initial current. In the present chapter we will see what is electrolysis and how it is useful in our day to day life.
we will study in this chapter
To see how electricity is conducted through a solid compound, a molten compound and an aqueous solution of the compound, do the following. Take two metal rods, a 6V battery, a bulb or an ammeter, wires. Take sodium chloride in a petri dish. Keep a burner and water in a beaker also. Connect the circuit as shown in the figure below. Bulb or an ammeter will visually indicate the passage of current.
notice the following :
the above experiment, instead of salt solution, try other solutions like
sugar solution, glycerin, alcohol, dilute sulphuric acid, copper sulphate
solution, acetic acid.
will notice the following :
above experiments show that there is a relationship between the passage of
electricity and the chemical reactions taking place due to it. All compounds
do not conduct electricity; and the state of the compound, whether molten or
aqueous, is an important factor.
definitions regarding electrolysis
2.Electrolyte : A compound that allows electric current to pass through
itself, when either in a molten state or in an aqueous solution, is called
an electrolyte. In the above experiment, solutions of sodium chloride,
copper sulphate, dilute sulphuric acids, acetic acid are electrolytes.
Strong electrolytes are those that allow large electric currents to be
passed through them. Solutions of sodium chloride, copper sulphate, dilute
sulphuric acid are examples of strong electrolytes. Weak electrolytes are
those compounds which are poor
conductors of electricity when they are in a molten state or in an aqueous
solution. The solution of acetic acid in the experiment above, showed that
it is a weak electrolyte.
: A compound which does not allow electric current to pass through itself in
any state, molten or aqueous, is called a non-electrolyte. In the above
experiments we have seen that sugar
solution, glycerin, alcohol, are non-electrolytes.
: The strips of metals
inserted in the electrolytes for conduction of electricity are called
electrodes. The metal electrode connected to the positive terminal of the
battery is called the anode (+).
The metal electrode connected to the negative terminal of the battery is
called the cathode (-).
On the other hand, in case of
molten NaCl, the bond length between the Na+ and the Cl-
ions has loosened. The bond is weakened. Hence the ions can become mobile
and conduct electricity.
In an aqueous solution of NaCl,
water molecules separate the Na+ and the Cl- ions.
This makes them very mobile. The
mobility is enhanced when two electrodes in the form of anode (+) and
cathode (-) are inserted in the salt solution. The Na+ ions get
attracted toward the cathode and the Cl- ions get attracted
toward the anode. The aqueous solution of NaCl
is therefore a good electrolyte.
can conclude from the above discussions that the movement of ions is
responsible for the flow of current in an electrolytic cell.
occurring during the passage of electricity in an electrolytic cell with
NaCl aqueous solution :
Dissociation of NaCl :
at the anode :
Cl- 1e- +
To summarize the process of electrolysis, we can say the following