Chlorine Gas - Practice Questions & MCQ

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Chlorine(Cl2) is considered one the most difficult concept.
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The products obtained when chlorine gas reacts with cold and dilute aqueous NaOH are :

$CI^{-} and\, CIO^{-}$

$CI^{-} and\, CIO_{2}^{-}$

$CIO^{-} and \, CIO_{3}^{-}$

$CIO_{2}^{-} and \, CIO_{3}^{-}$

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Chlorine(Cl2)

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 H2SO4 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 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.

$2 \mathrm{Al}+3 \mathrm{Cl}_{2} \rightarrow 2 \mathrm{AlCl}_{3}$

$\mathrm{P}_{4}+6 \mathrm{Cl}_{2} \rightarrow 4 \mathrm{PCl}_{3}$

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

$\mathrm{H}_{2}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl}$

$\mathrm{C}_{10} \mathrm{H}_{16}+8 \mathrm{Cl}_{2} \rightarrow 16 \mathrm{HCl}+10 \mathrm{C}$

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

$2 \mathrm{NaOH}+\mathrm{Cl}_{2} \rightarrow \mathrm{NaCl}+\mathrm{NaOCl}+\mathrm{H}_{2} \mathrm{O}$

$6 \mathrm{NaOH}+3 \mathrm{Cl}_{2} \rightarrow 5 \mathrm{NaCl}+\mathrm{NaClO}_{3}+3 \mathrm{H}_{2} \mathrm{O}$

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

$\mathrm{CH}_{4}+\mathrm{Cl}_{2} \stackrel{\mathrm{UV}}{\longrightarrow} \mathrm{CH}_{3} \mathrm{Cl}+\mathrm{HCl}$

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 oxidising 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. 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 woodpulp, bleaching 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 sterilising drinking water
It is used in the preparation of poisonous gases such as phosgene (COCl₂), tear gas(CCl₃NO₂), mustard gas (ClCH₂CH₂SCH₂CH₂Cl).

HCl, HBr and HI

Hydrogen Chloride

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

$\begin{array}{l}{\mathrm{NaCl}+\mathrm{H}_{2} \mathrm{SO}_{4} \: \overset{\mathrm{420K}}{\longrightarrow} \mathrm{NaHSO}_{4}+\mathrm{HCl}} \\ {\mathrm{NaHSO}_{4}+\mathrm{NaCl} \stackrel{823 \mathrm{K}}{\longrightarrow} \mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{HCl}}\end{array}$

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 ionises as follows:

$\mathrm{HCl}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O(l)} \rightarrow \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq})$

Its aqueous solution is called hydrochloric acid. High value of 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, 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

$\mathrm{NaI\: +\: H_{3}PO_{4}\: \rightarrow \: HI\: +\: NaH_{2}PO_{4}}$