Lecture 15- Chlorine (Cl) is a chemical element having atomic number 17Cl2.pdf
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Chlorine (Cl) is a chemical element with atomic number 17, known for its strong oxidizing properties and highest electron affinity. It was first isolated by Jan Baptist van Helmont in 1630, later characterized by Carl Wilhelm Scheele in 1774, and is primarily manufactured through electrolysis. Chlorine has various applications, including water purification, sanitation, and production of numerous chemical compounds, though it is also dangerous and toxic to life.
Lecture 15- Chlorine (Cl) is a chemical element having atomic number 17Cl2.pdf
- 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 except 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 400-4500C in presence of porous earthenware impregnated CuCl2 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. 175OC 190OC 2AuCl3 2AuCl + 2Cl2 Au + 3Cl2 375OC 600OC 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 : -340C Melting point : -1010C Vapour density : 2.48 (v/s air) Vapour pressure : 4800mmHg (200C) 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.