Page 62 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Where ‘z’ is called electrochemical equivalent (E C E) of the substance.
M = mass of material deposited.
Q = quantity of electricity passed through the electrolyte.
I = the current.
t = time in seconds for which current is passed.
Second law: If the same quantity of electric charge is passed through different electrolytes, the masses of the
substances liberated or deposited are proportional to their chemical equivalent weight.
Atomic weight
Equivalent weight =
Valency
Electrochemical Equivalent (ECE)
ECE of a substance is the mass of the substance liberated or deposited in electrolysis by the passage of 1
coulomb of charge. Its SI unit is kilogram/coulomb. It has the same value for one element but different for other
element.
Problem:

25x25 cm metal plate is to be copper plated. If the current is adjusted to 5ampere and has been passed for 40
minutes, find the thickness of deposited copper. Take ECE of copper= 0.000329 gm per coulomb and density=
8.2.
Area of plate = 25x25 = 625 sq cm.
Area of both the sides = 2x625 = 1250 sq cm
We know M=Zit and mass= density x volume (volume = area x thickness)
M = 0.000329x5x40x60

M = 8.9x1250x thickness
329x5x40x600
Thickness = = 0.0003459 cm
1250x89x1000000
Application of electrolysis
• Electroplating.
• Electro refining of metals.

• Electro typing
Electroplating
Electroplating is the deposition of a metal coating on a metallic or other conductive surface by electrolysis in an
electrolytic cell. Electroplating is widely used in giving an attractive appearance and finish to all types of industrial
products. In this process inferior metals are coated with costly metals such as silver, chromium etc to give better
appearance and rust proof surface.
Low pressure DC is always used for electroplating. It varies from 1 to 16 V depending upon the rate of plating. The
value of current is adjusted according to the metal deposited. The shunt dynamo is usually used for electroplating.
It delivers large current at low pressure and it requires a large commutator and brush gear. The generated voltage
of dynamo is controlled by the voltage regulator.
Nickel plating

The object and metal being plated is immersed in tank which containing the electrolyte. When PD is applied
positive ions drift to the cathode and metal is deposited on the object. The negative ions drift to the anode ie the
metal being plated is dissolves. The amount of metal deposited is directly proportional to the number of electrons.
This relationship is a reflection of faradays law of electrolysis. The object to be plated is made cathode. The anode
is usually the metal being plated. The article to be plated must have a chemically cleaned surface. The object is
immersed in a solution which contain the metal salt of the metal being plated. The solution is called electrolyte.

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CITS : Power - Electrician & Wireman - Lesson 13-19 CITS : Power - Electrician & Wireman - Lesson 13-19