CHEMISTRY TEXTBOOK

Try this...

• Arrange a simple set up as shown in
  the diagram above.


• The lamp will glow when circuit is
  complete.


• Prepare 5 % (mass/volume) solutions
  of cane sugar, acetic acid, sodium
  chloride and urea in distilled water.


• Check the electrical conductivity
  of these solutions using the above
  assembly. Compare these with that
  observed with distilled water.

i. The conducting and nonconducting

nature of solutions can be identified

by measurement of their conductivity.

Sucrose and urea do not dissociate in their

aqueous solutions. The conductivities of

these solutions are nearly the same as

that of water. These substances are called

nonelectrolytes.

On the other hand, substances like

potassium chloride, acetic acid, sodium

hydroxide, HCl dissociate in their aqueous

solutions. The conductivities of their

aqueous solutions are higher than that

of water. These are called electrolytes.

Electrolytes conduct electricity in molten

state or when dissolved in water.

ii. On the basis of high or low electrical

conductivity electrolytes are classified

into strong and weak electrolytes. The

substances such as ionic salts, strong

acids or bases are almost completely

dissociated in aqueous solutions. These

are strong electrolytes. The solutions

of strong electrolytes exhibit high

conductivities.

The weak acids and weak bases are

weak electrolytes. They dissociate to a

very small extent in aqueous solutions

and show lower conductivities than those

of strong electrolytes.

5.2.2 Electrolytic or ionic conduction :
Electrolytic conduction involves conduction
of electric current by the movement of ions
of the electrolytes. In this type of conduction
the charge transfer occurs in the form of
movement of ions through molten electrolytes
or the aqueous solutions of electrolytes.
Substances such as ionic salts, strong or weak
acids and bases are the electrolytes. These
dissociate into ions when dissolved in polar
solvents such as water. Ionic solids dissociate
into ions in molten state as well.

Conduction through electrolytic
conductors involves transfer of matter from
one part of the conductor to the other. It
means that the current flowing through an
electrolytic conductor is accompanied by a
chemical change.

5.2.3 Information provided by measurement
of conductivities of solutions :

Remember...

Electrolyte is a compound that

conducts electricity when molten or

in aqueous solution and breaks down into

ions during electrolysis.

5.3 Electrical conductance of solution :

According to Ohm's law, the electrical

resistance R of a conductor is equal to the

electric potential difference V divided by the

electric current, I :

R =

V

I^ (5.1)

The SI unit of potential is volt (V) and

that of current is ampere (A). The unit of

Switch Battery

Non conductive

frame

Electrodes

Solution

Lamp