• Most of the electrolytes are wither liquid (molten) ionic compounds or the aqueous solution of ionic compounds.

• Figure below shows the arrangement of ions of solid sodium chloride, molten sodium chloride and aqueous solution of sodium chloride.

• In solid, the ions are not free to move whereas in liquid (molten) and in aqueous solution, the ions can move freely.

ELECTROCHEMICAL CELL

VOLTAIC/GALVANIC CELL

• In voltaic cell, chemical is used to produce electricity. In this cell, chemical energy is converted to electrical energy.

• In electrolytic cell, electric current is flowed through an electrolyte to produce a chemical reaction. Electrical energy is converted to chemical energy, and the process is called electrolysis.

• There are 2 electrodes in an electrolytic cell:• The electrode connected to the positive terminal of the cell is

positive electrode and is given a name, anode.• The electrode connected to the negative terminal of the cell is

negative electrode and is called the cathode.

ELECTROLYTIC CELL

Electrolysis Of Molten Ionic Compound

• The ions in the electrolyte must be free to move to the electrodes for electrolysis to work.

• They are free to move in aqueous solution and in molten liquids. • However, the ions are in fixed positions in solid ionic compounds

- they cannot move around, so electrolysis does not work in solids.

Ions in ionic solids are arranged in a giant lattice and cannot move around

• When a molten (melted) ionic compound is electrolysed:• The positive ions are discharged at the cathode• The negative ions are discharged at the anode• For example, during the electrolysis of molten lead bromide:

-lead ions, Pb2+, move to the cathode and are discharged as lead-bromide ions, Br–, move to the anode and are discharged as

bromine• Half equations

-You should be able to write half equation for the reactions happening at the electrodes during the electrolysis of a molten electrolyte if you are given the formulae of the ions it contains.

Electrolysis Of Aqueous Solution

• In the electrolysis of aqueous solution only one ion involved in the selective discharge of ions at each electrode during the electrolysis and their ions are free to move.

•Theirs ion are cation and anion.

The positive ion are attracted to the negative electrode The negative ion are attracted to the positive ion

•Position of the ions in the electrochemical series

•Nature of electrode •Concentration of the ions in the solution

The ion is selected for discharge at an electrode depend on a number of factors, that is:

Position of ions in electrochemical series:

The figure shows an idealized drawing of a cell in which an aqueous solution of sodium sulphates electrolyzed

Electrochemical Series

INDUSTRIAL APPLICATIONS OF

ELECTROLYSIS

EXTRACTION OF SILVER

Silver is extracted from the ore-argentite (Ag2S). The process of extraction of silver iscalled as cyanide process as sodium cyanide solution is used.The ore is crushed, concentrated and then treated withsodium cyanide solution. This reaction forms sodium argentum cyanide Na[Ag(CN)2]. AgS+4NaCN⇌2Na[Ag(CN)2]+Na2S

The solution of sodium argentum cyanide combines with zinc dust and formssodium tetra cyanozicate and precipitated silver.This precipitated silver is called spongy silver.

Zn+2Na[Ag(CN)2]→Na2[Zn(CN)4]+2Ag

The spongy silver is fused with potassium nitrate to obtain pure silver.Then the silver obtained is purified by electrolytic process.

ELECTROPLATING• Electroplating is the process of plating one metal onto

another by hydrolysis, most commonly for decorative purposes or to prevent corrosion of a metal. There are also specific types of electroplating such as copper plating, silver plating, and chromium plating. Electroplating allows manufacturers to use inexpensive metals such as steel or zinc for the majority of the product and then apply different metals on the outside to account for appearance, protection, and other properties desired for the product. The surface can be a metal or even plastic.

• The cathode would be the piece to be plated and the anode would be either a sacrificial anode or an inert anode, normally either platinum or carbon (graphite form). Sometimes plating occurs on racks or barrels for efficiency when plating many products. Please refer to electrolysis for more information. In the figure below, the Ag+ ions are being drawn to the surface of the screw and it eventually becomes plated. The process is undergone using silver as the anode, and a screw as the cathode. The electrons are transferred from the anode to the cathode and is underwent in a solution containing silver.

Voltaic cell1. A cell that produces electrical energy when chemical reactions occur in it.

2. Energy changes in voltaic cell is chemical energy to electrical energy.

3. Produced when two different metals are dipped in an electrolyte and are connected by an external circuit.

4. The voltage of chemical cell depends on the distance between the two metals in the electrochemical series, where the further the distance between them, the higher is the voltage.

5. A more electropositive metal become the negative terminal of the cell. A less electropositive metal become positive terminal:

Negative Terminal

• More electropositive metal.

• Metal atom will release electrons that will flow through the external circuit. Metal atom becomes metal ion (becomes thinner)

Positive Terminal

• Less electropositive metal.

• The electron that flow from the external circuit are received by the positive ion in the electrolyte through this terminal.

Daniell cell it is an example of voltaic cell which consists of zinc electrode dipped in Zinc Sulphate solution, copper electrode dipped in copper (II) Sulphate solution and connected by a salt bridge or porous pot.

The function of porous pot or salt bridge is to allow the flow of ions through it so that the electric circuit is completed.

Main Uses of

Electrolysis

To predict the terminal of

chemical cell

To Predict the voltage of

chemical cell

To predict the metal

displacement reaction

To predict the selected ion

discharged at the electrode