Chlorine Gas - Cl2

What is Chlorine gas?

Chlorine is a green yellow gas with a very pungent odour that is twice as dense as air. It is a chemical element belongs to the halogen group with the symbol Cl. It was discovered in 1770’s and soon became useful as a commercial agent.It is found easily in natural state. It should be handled carefully because it is poisonous at low concentrations. Chlorine is very harmful and been used as chemical weapons throughout history.

Other name – Molecular chlorine

Cl2 Chlorine gas
Density 3.2 g/L
Molecular Weight/ Molar Mass 35.453 u
Boiling Point -34.04 °C
Melting Point -101.5 °C
Chemical Formula Cl2

Chlorine gas Structure – Cl2


Physical Properties of Chlorine gas – Cl2

Odour Odour of bleach
Appearance Yellow green gas
Covalently-Bonded Unit 1
Vapour Pressure 85.3 psig
pH 7.4
Solubility Slightly soluble in water

Chemical Properties of Chlorine gas – Cl2

  • Chlorine reacts with organic compounds and ammonia to form chloro-organics or chloramines. Chloramines are part of the group of chlorine compounds that have disinfectant properties and show up as part of chlorine residue test.
  • It acts as a reducing agent present in wastewater. These reactions are called chlorine demand. The reaction is as below.H2O + Cl2 → HCl + HClO

Uses of Chlorine gas – Cl2

  • Chlorine gas was used by the Germans as a chemical weapon against the allied troops during the First World War.
  • The most common use of chlorine in wastewater treatment is for disinfection.
  • Used in odor control and in the control of filamentous organisms in the activated sludge process.
  • Despite of all these it is used for preventing the spread of waterborne disease and the most common means of disinfection in use.

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