Page 165 - Chemistry ICSE Class X

Electrolysis 151

Why do molten electrolytes and solutions of electrolytes
conduct electricity
All electrolytes when dissolved in water or when melted, break up into free
–
+
ions. For example, when sodium chloride (Na Cl ) is melted or dissolved in
–
+
water, free sodium (Na ) and chloride (Cl ) ions are formed. These ions are
randomly distributed in the solution.
–
+
Na Cl (l) o Na + + Cl –
molten sodium sodium ion chloride ion
chloride (cation) (anion)
Fig. 6.2 When electrical potential is
–
+
NaCl(s) + H O(l) o Na (aq) + Cl (aq) applied across the solution, the cations
2
sodium water sodium ion chloride ion start moving towards cathode
chloride (cation) in solution (anion) in solution (–ve electrode), and anions start moving
When electrical potential is applied across the solution, the cations towards anode (+ve electrode)
start moving towards cathode (–ve electrode) and the anions towards
anode (+ve electrode).
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of electricity through the molten electrolyte or solution of electrolyte.
Some Important Terms Related to Electrolysis

ƒ Electrolysis. The process of chemical decomposition of an electrolyte
in a solution or in molten state, by the passage of electric current is
called electrolysis.
ƒ Electrolytes. The substances which furnish ions in aqueous solution
or on melting are called electrolytes.
Or
Substances which conduct electricity when dissolved in water or
when melted are called electrolytes.
ƒ Electrolytic cell. # EQPVCKPGT QT XGUUGN ſVVGF YKVJ VYQ GNGEVTQFGU KP Fig. 6.3 An electrolytic cell
which electrolysis is carried out is called electrolytic cell or voltameter.
ƒ Electrodes. The plate, rod or wire of a metal, graphite, or conducting
carbon through which the current enters and leaves the electrolytic cell
is called electrode. Electrodes are of two types: Anode and Cathode.
Š Anode. The electrode connected to the positive terminal of a battery
is called anode. At anode, oxidation takes place.
Š Cathode. The electrode connected to the negative terminal of a
battery is called cathode. At cathode, reduction takes place.
ƒ Ion. An atom or group of atoms carrying a positive or negative charge
is called an ion. There are two types of ions — the positively charged
and the negatively charged.
2+
+
Š The positively charged ion is called cation. For example, Na , Ca ,
3+
Al , etc. are cations.
–
–
Š The negatively charged ion is called anion. For example, Cl , OH
3–
2–
SO , PO , etc. are anions.
4
4
Electrolysis
What is electrolysis
The word electrolysis means breaking up by the action of electricity. It may
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