Lecture 15- Chlorine (Cl) is a chemical element having atomic number 17Cl2.pdf

Chlorine (Cl) is a chemical element having atomic number 17...........

1. Module: 3
Lecture: 15 Chlorine
Dr. N. K. Patel



N P T E L

93
Module: 3
Lecture: 15
CHLORINE
INTRODUCTION
Chlorine (Cl) is a chemical element having atomic number 17. It is the second
lightest halogen after fluorine. The element forms diatomic molecules under STP,
called dichlorine. It has the highest electron affinity and the third highest
electronegativity of all the elements; for this reason, chlorine is a strong oxidizing
agent.

Chlorine gas was obtained by Jan Baptist van Helmont in1630. The synthesis
and characterization of elemental chlorine occurred in 1774 by Carl Wilhelm
Scheele, who called it "dephlogisticated muriatic acid air," having thought he
synthesized the oxide obtained from the hydrochloric acid. Because acids were
thought at the time to necessarily contain oxygen, a number of chemists, including
Claude Berthollet, suggested that Scheele's dephlogisticated muriatic acid air must
be a combination of oxygen and the yet undiscovered element, and Scheele
named this new element within this oxide as muriaticum. In 1809, Joseph Louis Gay-
Lussac and Louis-Jacques proved that this newly discovered gas was the simple
element which was reconfirmed by Sir Humphry Davy in 1810, who named it
chlorine, from the Greek word chlōros meaning "green-yellow."

Chlorine can be manufacture by several methods such as electrolysis,
Deacon‘s, heating of auric acid and platonic chloride. All methods exce pt
electrolysis are costly. So, chlorine is largely manufacture by electrolysis process
MANUFACTURE
1. Using diaphragm cells
Chlorine can be obtained as co-product during the manufacture of caustic
soda by electrolysis process as discussed in Module: 3, Lecture: 9.
2. Deacon’s method
Hydrochloric acid is partially oxidizes to chlorine by heating of HCl gas with
oxygen (air) at 400-450
0
C in presence of porous earthenware impregnated CuCl 2 as
catalyst.

2. Module: 3
Lecture: 15 Chlorine
Dr. N. K. Patel



N P T E L

94
4HCl + O2 2Cl2 + 2H2O

OR

2CuCl2 2CuCl + 2Cl2
4CuCl + O2 2Cu2OCl2
Cu2OCl2 + 2HCl 2CuCl2 + H2O

Cl2 mixed with unconverted HCI and system is washed with cold water and
dried with conc. H2SO4. This is an old method for manufacture of chlorine and is not
in used now.
3. Other methods
Pure chlorine can also be prepared by heating Auric chloride (AuCl3)or
platonic chloride (PtCl4)in a hard glass tube.

175
O
C 190
O
C
2AuCl3 2AuCl + 2Cl2 Au + 3Cl2
375
O
C 600
O
C
PtCl4 PtCl2 + Cl2 Pt + 2Cl2

PROPERTIES

 Molecular formula : Cl2
 Molecular weight : 70.906gm/mole
 Appearance : Yellow green gas
 Odour : similar to house hold bleach
 Boiling point : -34
0
C
 Melting point : -101
0
C
 Vapour density : 2.48 (v/s air)
 Vapour pressure : 4800mmHg (20
0
C)
 In upper atmosphere, chlorine containing molecules such as chlorofluoro-
carbons have been implicated in ozone depletion.
 Elemental chlorine is extremely dangerous and poisonous for all life forms
 It is necessary to most forms of life, including humans, in form of chloride ions.
 It is the only acidic gas which turns damp blue litmus red and bleaches it to
white.
 It is two and a half times heavier than air. It becomes a liquid at −34 °C.
 The affinity of chlorine for hydrogen is so great that the reaction proceeds
with explosive violence in presence of light

3. Module: 3
Lecture: 15 Chlorine
Dr. N. K. Patel



N P T E L

95
USES

 Used for producing safe drinking water.
 Chlorinated compounds are used mostly for sanitation, pulp bleaching and
textile processing.
 Used for the manufacture of chlorates and it is important in organic chemistry,
forming compounds such as chloroform, carbon tetrachloride, polyvinyl
chloride, and synthetic rubber.
 Used in dyestuffs, petroleum products, medicines, antiseptics, insecticides,
foodstuffs, solvents, paints and plastics.
 As an oxidizing agent and in substitution reactions.
 In paper and pulp, solvents, explosives, plastics, pesticides and sanitation
 As a common disinfectant, chlorine compounds are used in swimming pools
to keep them clean and sanitary.