Chlorine Gas (Cl2) - Structure, Molecular Mass, Properties and Uses

Imagine walking into a public swimming pool and feeling confident that the water does not contain any bacteria or viruses that will prove detrimental to your health. Alternatively, consider the convenience of turning on a tap and finding that safe potable water is already available without any second thoughts formally taken. Such everyday comforts are realized through the ubiquitous use of chlorine gas in the water treatment and sanitation process.

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This Story also Contains

1. Physical Properties of Group 13 – 1
2. Group 13 - 2 Physical Properties
3. Hydrogen Chloride
4. Hydrogen bromide and Hydrogen iodide
5. Relevance and Applications
6. Some Solved Examples
7. Summary

Discovered in 1774 by Swedish chemist Carl Wilhelm Scheele, chlorine gas has over the years evolved to become not only one of the highly used elements but also one of the essential chemicals in many industries today, from health to industrial manufacturing. It's from this gas that among the world's most powerful disinfecting actions have been developed, revolutionizing thus how hygiene and sanitation are approached today. It efficiently kills a wide spectrum of pathogens and is really of great importance to the concern for safety regarding the hygiene of drinking water and swimming pools.

Physical Properties of Group 13 – 1

Chlorine gas, though of the halogen group in the periodic table, falls under Group 17 and not Group 13. But its physical properties are of importance. Chlorine is a greenish-yellow gas with a pungent, suffocating odour. It is denser than air; the density comes to about 3.21 grams per liter at room temperature. The melting and boiling points of chlorine are -101.5°C and -34.04°C respectively, making it a gas under standard conditions: well soluble in water to give a pale-yellow solution, soluble in organic solvents like carbon tetrachloride. Such physical properties make chlorine gas very reactive and easily dispersible, the boon and bane in its applications.

Preparation

It can be prepared by anyone of the following methods:

• By heating manganese dioxide with concentrated hydrochloric acid.
  $
  \mathrm{MnO}_2+4 \mathrm{HCl} \rightarrow \mathrm{MnCl}_2+\mathrm{Cl}_2+2 \mathrm{H}_2 \mathrm{O}
  $
  However, a mixture of common salt and concentrated $\mathrm{H}_2 \mathrm{SO}_4$ is used in place of HCl .
  $
  4 \mathrm{NaCl}+\mathrm{MnO}_2+4 \mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{MnCl}_2+4 \mathrm{NaHSO}_4+2 \mathrm{H}_2 \mathrm{O}+\mathrm{Cl}_2
  $
  By the action of HCl on potassium permanganate.
  $
  2 \mathrm{KMnO}_4+16 \mathrm{HCl} \rightarrow 2 \mathrm{KCl}+2 \mathrm{MnCl}_2+8 \mathrm{H}_2 \mathrm{O}+5 \mathrm{Cl}_2
  $

Properties

It is a greenish-yellow gas with a pungent and suffocating odour. It is about 2-5 times heavier than air. It can be liquefied easily into greenish-yellow liquid which boils at 239 K. It is soluble in water.
Chlorine reacts with a number of metals and non-metals to form chlorides.

$\begin{aligned} & 2 \mathrm{Al}+3 \mathrm{Cl}_2 \rightarrow 2 \mathrm{AlCl}_3 \\ & \mathrm{P}_4+6 \mathrm{Cl}_2 \rightarrow 4 \mathrm{PCl}_3\end{aligned}$

It has great affinity for hydrogen. It reacts with compounds containing hydrogen to form HCl.

$\begin{aligned} & \mathrm{H}_2+\mathrm{Cl}_2 \rightarrow 2 \mathrm{HCl} \\ & \mathrm{C}_{10} \mathrm{H}_{16}+8 \mathrm{Cl}_2 \rightarrow 16 \mathrm{HCl}+10 \mathrm{C}\end{aligned}$

With cold and dilute alkalies chlorine produces a mixture of chloride and hypochlorite but with hot and concentrated alkalies it gives chloride and chlorate.

$\begin{aligned} & 2 \mathrm{NaOH}+\mathrm{Cl}_2 \rightarrow \mathrm{NaCl}+\mathrm{NaOCl}+\mathrm{H}_2 \mathrm{O} \\ & 6 \mathrm{NaOH}+3 \mathrm{Cl}_2 \rightarrow 5 \mathrm{NaCl}+\mathrm{NaClO}_3+3 \mathrm{H}_2 \mathrm{O}\end{aligned}$

Chlorine reacts with hydrocarbons and gives substitution products with saturated hydrocarbons and addition products with unsaturated hydrocarbons.

$\stackrel{\text { CH }}{\mathrm{CH}_4}+\mathrm{Cl}_2 \xrightarrow{\mathrm{UV}} \mathrm{CH}_3 \mathrm{Cl}+\mathrm{HCl}^{-}$

Chlorine water on standing loses its yellow colour due to the formation of HCl and HOCl. Hypochlorous acid (HOCl) so formed, gives nascent oxygen which is responsible for oxidizing and bleaching properties of chlorine.

Chlorine is a powerful bleaching agent; bleaching action is due to oxidation. It bleaches vegetable or organic matter in the presence of moisture. The bleaching effect of chlorine is permanent.

$\mathrm{Cl}_2+\mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{HCl}+\mathrm{O}$

Uses

• It is used for bleaching wood pulp, cotton, and textiles
• It is used in the extraction of gold and platinum
• It is used in the manufacture of dyes, drugs, and organic compounds such as CCl₄, CHCl₃, DDT, refrigerants, etc.
• It is used in sterilizing drinking water
• It is used in the preparation of poisonous gases such as phosgene (COCl₂), tear gas(CCl₃NO₂), and mustard gas (ClCH₂CH₂SCH₂CH₂Cl).

Group 13 - 2 Physical Properties

The chlorine gas is made up of a diatomic molecule with the chemical formula Cl₂. The gas is highly electronegative in nature and hence acts as an excellent oxidizing agent because of its electronegative nature and electron affinity. It disproportionates in water to form hydrochloric acid, HCl, and hypochlorous acid, HClO—this reaction forms the basis for its disinfectant properties. Chlorine gas is also known to react with a wide range of substances, including metals, nonmetals, and organic compounds. Its reactivity and toxicity mean it has to be handled and stored safely, mostly pressurized in cylinders or as a liquid under pressure. Knowing this kind of information about properties is quite important in using chlorine gas both safely and effectively in various settings.

Hydrogen Chloride

Preparation

In the laboratory, it is prepared by heating sodium chloride with concentrated sulphuric acid.

$\begin{aligned} & \mathrm{NaCl}+\mathrm{H}_2 \mathrm{SO}_4 \xrightarrow{420 \mathrm{~K}} \mathrm{NaHSO}_4+\mathrm{HCl} \\ & \mathrm{NaHSO}_4+\mathrm{NaCl} \xrightarrow{823 \mathrm{~K}} \mathrm{Na}_2 \mathrm{SO}_4+\mathrm{HCl}\end{aligned}$

HCl gas can be dried by passing through concentrated sulphuric acid.

Properties

It is a colourless and pungent-smelling gas. It is easily liquefied to a colourless liquid (b.p.189 K) and freezes to a white crystalline solid(f.p. 159 K). It is extremely soluble in water and ionizes as follows:

$\mathrm{HCl}(\mathrm{g})+\mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{H}_3 \mathrm{O}^{+}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq})$

Its aqueous solution is called hydrochloric acid. The high value of the dissociation constant (K_a) indicates that it is a strong acid in water. It reacts with NH₃ and gives white fumes of NH₄Cl.

$\mathrm{NH}_3+\mathrm{HCl} \rightarrow \mathrm{NH}_4 \mathrm{Cl}$

When three parts of concentrated HCl and one part of concentrated HNO₃ are mixed, aqua regia is formed which is used for dissolving noble metals, e.g., gold, and platinum.

Uses

• It is used in the manufacture of chlorine, NH₄Cl, and glucose (from corn starch).
• It is used for extracting glue from bones and purifying bone black.
• It is used in medicine and as a laboratory reagent.

Hydrogen bromide and Hydrogen iodide

$\begin{aligned} & \mathrm{NaI}+\mathrm{H}_3 \mathrm{PO}_4 \rightarrow \mathrm{HI}+\mathrm{NaH}_2 \mathrm{PO}_4 \\ & \mathrm{NaBr}+\mathrm{H}_3 \mathrm{PO}_4 \rightarrow \mathrm{HBr}+\mathrm{NaH}_2 \mathrm{PO}_4\end{aligned}$

In the laboratory, HBr and HI are prepared in the following ways:

$\begin{aligned} & 2 \mathrm{P}(\text { red })+3 \mathrm{Br}_2 \rightarrow 2 \mathrm{PBr}_3 \xrightarrow{+6 \mathrm{H}_2 \mathrm{O}} 6 \mathrm{HBr}+2 \mathrm{H}_3 \mathrm{PO}_3 \\ & 2 \mathrm{P}(\text { red })+3 \mathrm{I}_2 \rightarrow 2 \mathrm{PI}_3 \xrightarrow{+6 \mathrm{H}_2 \mathrm{O}} 6 \mathrm{HI}+2 \mathrm{H}_3 \mathrm{PO}_3\end{aligned}$

Relevance and Applications

There are a number of industries and public health initiatives where chlorine gas is put into practice every day. Mainly applied in purifying water to kill bacteria, viruses, and many other types of pathogens, it works to ensure safe drinking water across the globe. In the manufacture of paper, chlorine is broadly used in textile production and plastics like polyvinyl chloride or PVC. This, however, is a fairly versatile plastic used in construction and packaging. Chlorine compounds in the medical field are antiseptics and disinfectants; hence, these will prove useful in avoiding infections. It is further used by many pharmaceutical firms for making a large number of remedial pharmaceutical products, some of which are life-saving drugs. However, since chlorine itself is a toxic and corrosive gas, causing respiratory troubles and skin irritations, it needs handling with due care. Proper measures of safety and regulations related to handling such a dangerous gas will keep their risks under check.

Recommended topic video on (Chlorine gas)

Some Solved Examples

Example 1
Question:

When O₃ reacts with HCl, it converts HCl into

1)HClO

2) (correct)Cl₂

3)Cl^-

4)ClO₃^-

Solution:

As we have learned,

Halides generally react with good oxidizing agents and are converted to the respective halogen. Thus, ozone oxidizes HCl to form Chlorine gas.

$2 \mathrm{HCl}+\mathrm{O}_3 \rightarrow \mathrm{Cl}_2+\mathrm{H}_2 \mathrm{O}+\mathrm{O}_2$

Hence, the answer is the option (2).

Example 2
Question:

Pure Cl₂ is obtained by heating

1)AgCl

2)MgCl₂

3) (correct)AuCl₃

4)FeCl₃

Solution:

As we have learnt,

Pure Chlorine can be obtained by heating the chlorides of metals having low reactivity like Au or Pt. The reactions are given as,

$2 \mathrm{AuCl}_3 \xrightarrow{\Delta} 3 \mathrm{Cl}_2+2 \mathrm{Au}$

$\mathrm{PtCl}_4 \xrightarrow{\Delta} 2 \mathrm{Cl}_2+\mathrm{Pt}$

Hence, the answer is the option (3).

Example 3
Question:

When sodium thiosulphate reacts with Cl₂ it forms

1)NaOH

2) (correct)NaHSO₄

3)Na₂S₂O₃

4)Na₄S₄O₆

Solution:

As we have learnt,

Reaction of Chlorine with Sodium thiosulfate,

_{$\mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3+4 \mathrm{Cl}_2+5 \mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{NaHSO}_4+8 \mathrm{HCl}$}

Hence, the answer is the option (2).

Summary

Among the myriad important chemicals that find versatile applications in almost all spheres of human life is water purification, through industrial manufacturing, to healthcare-stands chlorine gas. The physical properties, such as high reactivity and good solubility, make chlorine gas a good disinfectant and a valuable industrial reagent. However, its very toxic nature does guarantee that extra care is exercised during its handling and stringent safety measures are ensured.