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Applications of Electrolysis- Physics Guide for Class 8

Applications of Electrolysis Class 8 Science Guide

Information about Applications of Electrolysis

Title

Applications of Electrolysis

Class

Class 8

Subject

Class 8 Physics

Topics Covered

  • Applications of Electrolysis
  • Process of electroplating
  • Practical Applications of Electroplating
  • Faraday's Discovery
  • Electro-Magnetic Induction


Applications

The chemical effects of current (electrolysis) have some important scientific and industrial applications. 

Some of these applications are: 
  1. Extraction of metals from ores: Certain metals are extracted from their ores by the process of electrolysis. For example, metals like aluminium, sodium, potassium, calcium are extracted by this method.
  2. Electrorefining of metals: It is the process of obtaining pure metal from the impure one by the process of electrolysis. For example, in electrorefining of copper, a pure copper rod is made the cathode, and the impure copper rod as anode, with copper sulphate solution taken as the electrolyte.
  3. Electroplating: The process of depositing a thin layer of any desired metal on another material, by the passage of electric current, is known as electroplating. We can demonstrate this process through the following activity. 

Activity 1
  • Take two conducting plates (10cm × 4cm), one of zinc and the other of copper.
  • Take 250 ml of distilled water in a clean and dry beaker.
  • Dissolve two table spoonful of copper sulphate in it. 
  • Add a few drops of dilute sulphuric acid (using appropriate precautions) to make it more conductive. 
  • Connect the copper electrode to the positive terminal and the zinc electrode to the negative terminal of the battery.
  • Allow a steady current to pass through this electrolyte for 20-30 minutes.
  • Now, carefully take out the plates from the solution.
What do we observe? Do we find a coating on one of the plates? 
We will find a reddish copper coating on the zinc plate (cathode) connected to the negative terminal of the battery. It is copper, from copper sulphate solution, that has got deposited on this zinc electrode. We call this process of depositing a thin layer/ coating of any desired metal on another metallic object (by passing an electric current), as electroplating

How does this deposition on the electrode happen?
To understand this, let us trace the flow of charges (ions). When electric current is passed through the copper sulphate solution, the copper sulphate solution dissociates into copper and sulphate ions. The free mobile copper ions are drawn to the cathode (zinc plate), get converted into copper atoms and then get deposited on it. Sulphate ions move to the cooper plate (anode) where they react with copper to form copper sulphate again. Thus, copper is effectively removed from the anode and deposited on the cathode.

Process of electroplating

Some conditions that help in getting a smooth and firm deposit during electroplating.
  1. The article, to be electroplated, should be made the cathode of an electrolytic cell.
  2. The anode is made of that pure metal which is to be coated on the article.
  3. A suitable soluble salt of the anode metal is taken as the electrolyte.

Practical Applications/Need of Electroplating

Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of different metals.

Some practical reasons for which object/articles are electroplated.
  1. To improve/alter their appearance: We all have seen the shining handles of bicycles and bath taps which are otherwise made of iron. This is done by electroplating them with chromium or nickel. Similarly, articles of base metals are often coated with precious metals to make them look more attractive.
  2. To provide a protective/strengthening coating: We often find a chromium plating on bath taps, car bumpers, bicycle handles, towel rails, kitchen gas burners, wheel rims and so on. The chromium deposit not only provides a shiny appearance but also helps to avoid corrosion and effects of 'wear and tear' and scratches. Some coatings also help to increase the strength of the base metal.
  3. To minimise the cost: We know that some of the metals, like gold, silver, platinum, nickel and chromium are very expensive. It would not be (generally) economical to make the whole object out of these metals. So the object/article is made from a less expensive metal and only a thin coating of the expensive metal is deposited over it. For example, artificial jewellery is often made by electroplating gold or silver on less expensive metals.

Faraday's Discovery

A very important phenomenon was discovered in 1831 by Michael Faraday. (A similar discovery, in that very year, was made independently by Josheph Henry.) This phenomenon is, now, the basis of production of (almost) all large scale electricity produced in the world.

It is because of this reason that it is often said:
"Had there been no Faraday, there would have been no electricity." 

The magnetic effects of electric currents can be viewed as conversion of electrical energy into magnetic energy. Faraday's discovery was, in a way, the reverse of these magnetic effects of current. He showed that we can get electricity from magnetism. To understand Faraday's discovery, let us perform the following activity.

Activity 2
  1. Take a hollow cylindrical pipe of iron and wind a large number of turns of well-insulated copper wire on it.
  2. Clean the two ends of the wire and attach a torch bulb/LED to it.
  3. Now, take a strong bar magnet and move it rapidly towards the centre of the pipe (without touching it). 
What do we observe?
  • We find that the bulb glows. However, it glows only for a while and stop glowing  as soon as the magnet is stopped.
  • If we now withdraw the magnet away from the coil, we find that the bulb again 'glows up' momentarily. 
  • We are, thus, getting electricity through this motion of the magnet near/through a coil. 

Electro-Magnetic Induction

The phenomenon, in which electric current can be generated by a changing magnetic field, is known as electro-magnetic induction.

The discovery and understanding, of the phenomenon of electro-magnetic induction, is based on a series of experiments carried out by Faraday and Henry.

Their experimental observations can be summed up as follows:
  1. Whenever there is a relative motion between a magnet and a coil, that is part of an electric circuit, a current flows through the coil.
  2. The flow of current stops as soon as the magnet and the coil are at rest with respect to each other.
  3. The faster is the relative motion, between the magnet and the coil, the more is the current that flows through the coil.
  4. The direction of current, obtained by moving the magnet away from the coil, is opposite to its direction when the magnet is moved towards the coil.
The phenomenon of electro-magnetic induction forms the underlying principle of all modern day generators and transformers.
The generators help us to convert mechanical energy into electrical energy. Today's civilisation owes its progress, to a very great extent, to the discovery of this phenomenon of electro-magnetic induction. 

Points to Remember

  • The tin cans, we use for storage of food items, are made by electroplating tin onto iron. As tin is less reactive than iron, the food items do not come into contact with iron and are protected from getting spoiled.
  • An artificial satellite may have a long metallic chain/cable (≈10 km long) attached to it. When the satellite orbits a particular planet, it cuts the magnetic field lines of that planet. An induced e.m.f. (motional e.m.f.) gets developed in the metallic chain/cable. This (motional) e.m.f. can supply electrical power to the satellite.
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