Discovery
The Swedish chemist Carl Wilhelm Scheele first prepared chlorine in 1770 by treating hot concentrated hydrochloric acid with manganese dioxide.
Introduction
Some Basic Features of Chlorine
| Symbol | Cl |
| Formula | Cl2 |
Position of Chlorine in the Periodic Table
1.Chlorine is placed second after fluorine in group VIIA.
2. Other members of this group are fluorine, bromine, iodine and astatine (the last member is radioactive).
Occurrence
Chlorine belongs to the 'halogen' family. All the elements of this family are non-metals. They exhibit similar properties and they all form salts similar to sodium chloride.
Preparation of Chlorine
From concentrated hydrochloric acid by oxidation
Chlorine can be prepared by removing the hydrogen from hydrochloric acid using an oxidizing agent. Any oxidising agent such as manganese dioxide, lead dioxide, trilead tetroxide, potassium permanganate or potassium dichromate can be used. Firstly, the oxidising agents are taken in the round bottomed flask.
Physical Properties of Chlorine
Vapor density
The vapor density of chlorine = 35.5, which is nearly 2.5 times denser than air (Vapor density of air = 14.4).
Chemical Properties of Chlorine - Combustibility
Chlorine does not burn in air, but supports the combustion of many substances in it, forming the respective chlorides.
Chemical Properties of Chlorine - Addition Reactions
With metals
Besides the above reactions of chlorine with metals, chlorine also undergoes addition reactions with heated metals like aluminium, zinc, iron, etc. to form their chlorides. Metals with variable valencies always form the chloride of the higher metallic valency.
Chemical Properties of Chlorine - As an Oxidizing Agent
All the reactions especially those of chlorine with metals are examples of redox reactions.
Affinity for Hydrogen
Chlorine combines with free hydrogen to form hydrogen chloride. It can also react with the hydrogen present in other compounds such as water, ammonia, hydrocarbon, hydrogen sulphide etc.
Bleaching Action of Chlorine
Chlorine bleaches (removes the color) organic colors by the process of oxidation in presence of moisture.
Displacement of the Halogens by Chlorine
Halogens are the most electronegative elements. Fluorine is the most electronegative, followed by chlorine then bromine and then iodine.
Reaction with Slaked Lime
Chlorine reacts with slaked lime to give bleaching powder. Sprinkle some slaked lime powder into a jar of chlorine. Close the gas jar with a disc and shake it up. Soon the greenish yellow color of chlorine disappears and a off-white powder is left behind in the jar.
Tests for Chlorine
1. Chlorine is a greenish yellow gas with a pungent and irritating odor.
2. It turns wet blue litmus paper red and then bleaches it.
Uses of Chlorine
The strong oxidizing action of chlorine destroys organic matter like bacteria, fungus and other micro-organisms. In most of the advanced countries chlorine has now been mostly replaced by ozone, which is more environment friendly disinfectant.
Summary
Chlorine is prepared by the oxidation of concentrated hydrochloric acid using oxidising agents like manganese dioxide, lead dioxide, trilead tetra oxide, potassium permanganate and potassium dichromate.
