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The Chemistry Behind Chlorine And Hydrogen Chloride

Introduction

In Chemistry, even though Hydrogen Chloride and Chlorine are different elements we tend to study them together. Besides, they share a close relationship, for example, most HCl is produced as a co-product of reactions involving chlorine. So this basically makes it desirable to consider the two chemical substances together. That being said, here we will look at the methods for the preparation of Hydrogen Chloride and Chlorine.

Hydrogen Chloride

Hydrogen Chloride was first prepared in the year 1648 by Glauber by heating sodium chloride with concentrated

$$\begin{array}{l}H_{2}SO_{4}\end{array}$$
In the year 1840, Davy showed that HCl is a compound of chlorine and hydrogen. The common name for hydrochloric acid is muriatic acid.

Preparation of Hydrogen Chloride

Muriatic acid is prepared by warming NaCl crystals with concentrated H2SO4 (Sulphuric acid).

$$\begin{array}{l}NaCl + H_{2}SO_4{\rightarrow }NaHSO_{4} + HCl\end{array}$$

Usually, most of the hydrogen chloride/hydrochloric acid that is formed is a co-product of some other chemical reactions. HCl is also formed by the chlorination of hydrocarbons.

Properties of Hydrogen Chloride

• HCl is an uncoloured gas and has a pungent aroma.
• Hydrochloric acid is the aqueous solution of hydrogen chloride.
• HCl is soluble in water.
• It liquefies at 189K to form a colourless liquid and freezes at 159k to form a white solid.

Uses of Hydrogen Chloride

• HCl is used in the preparation of chlorine, aqua regia, and other chlorides.
• It is used as a solvent to dissolve noble gases.
• It acts as a reagent in laboratories.

Chlorine

Chlorine has an atomic number 17 and occupies group 17 and period 3 in the periodic table. The chemistry behind chlorine plays a vital role in meeting the daily requirements. At the same time scientists around the world work on the advancements in renewable energies and modern medicines. In the year 1774, Scheele discovered the presence of this greenish-yellow gas by observing the action of HCl on MnO2. This gas wasn’t given a name until Davy rooted its elementary description and recommended the name based on the colour of the gas.

Preparation of Cl2

This gas can be prepared in any of the following processes:

• When Manganese dioxide is heated with concentrated HCl.

MnO2+4HCl→MnCl2+Cl2+2H2O

• Conc. HCl acid can be replaced by a combination of conc. H2SO4 and common salt.

4NaCl+MnO2+H2SO4→MnCl2+4NaHSO4+2H2O+Cl2

• HCl in action with potassium permanganate gives

2KMnO4+16HCl→2KCl+2MnCl2+8H2O+5Cl2

Other processes to prepare Chlorine.

Electrolytic process: In this process, brine undergoes electrolysis. Brine is a concentrated solution of sodium chloride. After electrolysis Cl2 is discharged at the anode.

Deacon’s method: In this method Cl2 is obtained by oxidising HCl gases with oxygen in the presence of a catalyst. CuCl2 acts as a catalyst in this process at 723 K.

Properties of Cl2

• Cl2 is a gas with greenish-yellow colouration and pungent odour.
• The nature of the gas is poisonous.
• The gas boils at 239.11K and melts at 171.6K.
• Chlorine water is formed when Cl2 is dissolved in water. The yellow colour of the water gets dissipated when exposed to the sunlight due to the formation of hypochlorous acid and HCl. This hypochlorous acid formed is unstable, hence it decomposes to give nascent oxygen which is responsible for the bleaching and oxidising action of Cl2.

Cl2 + H2O → HCl + HOCl

HOCl → HCl + [O]

• Cl2 is highly electronegative in nature
• Cl2 has great affinity towards hydrogen. It reacts with hydrogen to form HCl.

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