We have observed in our daily life, that a jewellery of silver is looked like a gold jewellery but it is not that. Only a layer of Gold is electroplated over the silver jewellery. Have you ever thought how electroplated is carried out ?? In this article we will learn about this process in detail.Before going through electroplating, we must know about ELECTROLYSIS.
The word ” Electrolysis ” contains two terms, one is electro and other is lysis.
Electro means ” to flow of electron ” that is electricity where as lysis means ” to break down” .
Hence, Electrolysis means to breakdown of a chemical substance by the passage of electricity. But this break down requires a condition and the condition is that the substance should be in molten state or in solution state.
Definition of Electrolysis :
When elecrtricity passes through a chemical substacne in molten state or in solution state, it breaks down into its components. This process is called as Eelctrolysis.
Definition of Electrolyte :
The chemical substance in molten state or in solution state which breaks down into its components by the passage of electricity, is called as electrolyte.
Examples : Hydrochloric acid, sulphuric acid, nitric acid, sodium chloride, copper sulphate etc.
i ) It conducts electricity when it is in molten state or in fused state or in soluiton state.
ii ) It breaks down into its components when electricity passes throuhg its molten state or fused state or solution state.
iii ) It conducts electricity through migration of ions.
Definition of Non electrolyte :
The chemical substance in molten state or in solution state which does not break down into its components by the passage of electricity, is called as non-electrolyte.
Examples : Plastic, Distilled water or pure water, alcohol, kerosene, benzene, glucose urea etc.
Types of Electrolytes :
There are two types of electrolytes
1 ) Strong electrolyte
2 ) Weak electrolyte
1 ) Strong Electrolytes :
The elctrolytes which are completely dissociates into its components when the electricity passes through its molten state or fused state or solution state, are called as the strong electrolyte.
i ) It allows a large amount of electricity to pass through them.
ii ) It dissociates completely in molten state or solution state on passing electricity.
iii ) Strong electrolytes are good conductor of electrocity .
iv ) It allows a bulb to glow brightly.
v ) Its solution contains only free and mobile ions.
Acid : Hydrochloric acid, nitric acid, sulphuric acid etc
Salts : Sodium chloride ( molten or solution ), Lead bromide ( molten ), Copper chloride ( aqueous ) and copper sulphate ( aqueous ) etc.
Base : Sodium hydroxide and Potassium hydroxide etc.
2 ) Weak Electrolyte :
The elctrolytes which partially dissociate into its components when the electricity passes through its molten state or fused state or solution state, are called as the weak electrolyte.
i ) It allow a small amount of electricity to pass through them.
ii ) It dissociates partially in molten state or solution state on passing electricity.
iii ) Strong electrolytes are poor conductor of electrocity .
iv ) It allows a bulb to glow dimly.
v ) Its solution contains ions as well as molecules.
Acid : Carbonic acid, Oxalic acid and Accetic acid etc.
Base : Ammonium Hydroxide and Calcium Hydroxide etc
Salts : Ammonium Carbonate and Lead Acetate etc.
Electrolytic Cell :
A non conducting vessel which converts electrical energy into chemical energy is called as electrolytic cell.
The electrolytic cell in which electrolysisof water is carried out, is called as Voltameter.
Now, students……………. you are thinking that if the electrolytic cell is non conducting then how would we supply electricity to the solution so that electrolysis occurs. To overcome this problem, two metal plates or wires or graphite rods or gas carbon rods are immersed into the solution thorugh which the current enters and leaves the electrolytic cell. This metal plates or wires or graphite rods or gas carbon rods are called as Electrodes.
Types of Electrodes :
There are two types of electrodes one is anode and other is cathode
1 ) Anode :
The electrode which is connected with the positive terminal of the battery, is called as Anode.
Properties of Anode :
i ) Anode is the electron deficient and therfore it is electron acceptor.
ii ) Oxidation takes place at anode.
iii ) Anion is migrated towards anode.
2 ) Cathode :
The electrode which is connected with negative terminal of the battery, is called as cathode.
Properties of Cathode :
i ) Cathode is the electron rich electrode and therfore it is electron donor.
ii ) Reduction takes place at anode.
iii ) Cation is migrated towards cathode.
Electrolysis of Water :
As we know that pure water or distilled water is non electrolyte, it is acidified so that it conducts electricity.
Electrolyte : Distilled water + Dilute sulphuric acid.
[ Dilute Hydrochloric acid and Nitric acid are not used to acidify distilled water as these acids are volatile at room temperature but dilute sulphuric acid is non volatile at room temperature. ]
Electrodes : Platinum ( as it is inert ) connected with the battery via copper wires.
Ionisation of acidified water :
H2O ⇌ H+ + OH–
A molecule of distilled water ionises into hydrogen ion ( H+ ) or H3O+ and hydroxyl ion ( OH– )
Reaction at Cathode :
H+ + e– → [ H ]
[ H ] + [ H ] →H2 ( gas )
Hydrogen ion migrates towards cathode and gains an electron to give nascent hydrogen and this nascent hydrogen combines with other nascent hydrogen to give hydrogen gas. Hence, hydrogen gas is produced at cathode.
Reaction at Anode :
OH– – e– → OH
4OH → 2 H2O + O2 ( gas )
Hydroxyl ion migrates to anode and loses an electron to become OH and then four OH combines to give two molecules of water and one molecule of oxygen gas. Hence, oxygen gas is produced at anode.
1 ) Hydrogen ion ( H+ ) is collected at cathode.
2 ) Hydrogen gas is produced at cathode.
3 ) Hydroxyl ion ( OH– ) is collected at anode.
4 ) Oxygen gas is produced at anode.
5 ) Dilute sulphuric acid is used to acidify distilled water. It catalyse the ionisation of water. Hence, electrolysis of acidified water is considered catalysis.
Application of Electrolysis :
1 ) Extraction of Metals
2 ) Purification of Metals
3 ) Electroplatig
1 ) Extractio of Metals :
Extraction of Aluminium :
Electrolytes : 60 parts of Cryolite + 20 Parts of fluospar ( Molten state )
20 Parts of pure alumina is added to the aobve mixture in molten state.
Cathode : Gas carbon
Anode : Graphite rods
Now, battery is switched on and electricity is passed through anode into the solution. Then the electrolyte ionises into its components which is given below.
Al2O3 ⇌ 2Al+3 +3 O-2
Reaction at Cathode :
Aluminium ion migrates towards cathode as it is electron rich. Then it gains 3 electrons and beocme Neutral Aluminium.
Al+3 + 3e → Al
Reaction at Anode :
Oxide ion migrates towards anode it is connected with the positive terminal of the battery. There it loses 2 electrons and become nascent oxygen. As soon as nascent oxygen is produced, it combines with other oxygen atom to become oxygen molecule.
O-2 – 2e– → [ O ]
[ O ] + [ O ] → O2