Page 184 - Chemistry ICSE Class X
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170 ICSE Chemistry – 10
Let us say it Again
Electrolyte. A substance which furnishes ions in a solution or when melted is called an electrolyte. Sodium chloride and
sodium hydroxide are typical electrolytes.
Nonelectrolytes. The compounds which do not conduct electricity both in pure molten state and in their solutions are
called nonelectrolytes. Alcohol, urea, sugar, etc. are nonelectrolytes.
Flow of electricity through solution. The movement of ions towards respective electrodes causes the flow of electricity
through a molten electrolyte or through an aqueous solution of an electrolyte.
Electrolysis. The process of splitting of an electrolyte with the help of electricity is called electrolysis.
During electrolysis, cations get reduced at cathode and anions get oxidised at anode.
Electrolysis of molten sodium chloride gives sodium metal at cathode and chlorine gas at anode.
Electrolysis of an aqueous solution of sodium chloride gives chlorine at anode, hydrogen at cathode and a solution of
sodium hydroxide (NaOH) around cathode.
Classification of electrolytes. Electrolytes are classified as
Strong electrolytes
Weak electrolytes
Application of electrolysis. The principle of electrolysis is used in electrometallurgy, electrorefining of metals,
electroplating, etc.
Highly electropositive metals like sodium, potassium, magnesium, aluminium, etc. are obtained by the electrolysis of
their molten compounds.
Electroplating. The process of depositing a thin layer of any superior metal over an object of an inferior metal with the
help of electricity is called electroplating.
Chrome plating of iron or brass is done to protect it from corrosion and also for giving it a decorative look.
During electroplating, the object to be electroplated is made cathode and a thin sheet of pure metal to be electroplated
is made anode.
Reactivity (or activity) series of metals. The arrangement of metals in a vertical column in the order of decreasing
reactivity is called reactivity (or activity) series of metals.
The electropositive character decreases as we go down from top to bottom in the activity series of metals.
A more electropositive metal displaces less electropositive metal from its salt solution.
More reactive metals occur in the combined form, whereas less reactive metals occur as free metals in nature.
The metals which occur in the upper part of the electrochemical series have high tendency to get oxidised and give
their cations.
The cations of the most electropositive metals, i.e., metals which appear near the top of the electrochemical series, do
not get easily discharged at the cathode during electrolysis.
The cations of the metals which appear below hydrogen in the electrochemical series get discharged (or reduced)
more easily at the cathode during electrolysis.
The tendency of anions towards oxidation at the anode follows the order,
–
–
–
–
–
OH > I > Br > Cl > NO > SO 2–
3 4
The higher the concentration of an ion in the solution, higher is its tendency for discharge at the respective electrode
in preference to the ion having lower concentration.
