Properties.

Degree of electrolytic dissociation of HCl is quite high. It makes up 92,6% in a 0,1 M solution at 18 ^oC (therefore, HCl is a strong acid).

Like other acids, HCl reacts:

HCl + [M, MO, M(OH) _n, salts]

HCl reacts also with strong oxidants:

NaClO + 2 HCl = H₂O + NaCl + Cl₂

HCl + [MnO₂, KMnO₄, PbO₂]:

PbO₂ + 4HCl_(conc.)= PbCl₂ + Cl₂ + 2 H₂O (like MnO₂)

Ion Cl^- can act as a ligand in coordination compounds:

CuCl₂ + 2Cl^- = [CuCl₄] ^{2 -}

Chlorides mostly are well water-soluble (exceptions are PbCl₂, AgCl, CuCl, and AuCl).

Oxygen compounds of chlorine. Chlorine can display oxidation states from +1 to +7 in compounds with oxygen. Among the most interesting are oxygen-containing acids and their salts.

Cl₂ has no direct reaction with O₂ due to Cl—O bond weakness and positive values of standard G^o of such compounds formation. Therefore, all oxides of chlorine are prepared in indirect way!

The names of oxygen-containing acids:

HClO hypochlorous (Cl +1)

HClO₂ chlorous (Cl +3)

HClO₃ chloric (Cl +5)

HClO₄ perchloric (Cl +7)

Cl₂O (dichlorine monoxide). It is a toxic gas with a strong smell, of brownish colour, b.p = 3,80 ^oC. A molecule Cl₂O has an angular shape, its valence angle is 111^о. At heating it explodes forming Cl₂ and O₂. It can explode at contact with organic materials and even at transition into the liquid state.

Preparation: 2Cl₂ + 2HgO = Cl₂O + HgCl₂^. HgO

Properties. It readily dissolves in water (1 volume : 200 volumes Cl₂O), it is the anhydride of hypochlorous acid HClO:

Cl₂O + H₂O = 2HClO;

Cl₂O + 2NaOH = 2NaClO + H₂O

HClO (hypochlorous acid). It exists only in the diluted solutions (maximal concentration at 20^о C makes up only 0,03 M), it is very weak acid (K_HClO = 4^.10^-8) and strong oxidant. HClO can be obtained at dissolution of Cl₂ in water:

Cl₂ + H₂O HCl + HClO (hypochlorous).

Among two acids that are the products of disproportionation of Cl₂, hydrochloric and hypochlorous, the first one is very strong, and the second is weak (weaker a H₂CO₃).

This sharp difference in strength of both acids is used for their separation. If to shake up a powder of chalk CaCO₃ in water and after it to pass through the suspension gaseous Cl₂, the acid HCl, which is formed, reacts with chalk, therefore removing itself:

CaCO₃ + 2HCl = CaCl₂ + CO₂ + H₂O

and the remaining HClO accumulates in the solution.

The practical method of preparation of hypochlorites is based on the use of interaction of Cl₂ with water_. As both compounds are products and stand in the right hand side of the equation, HCl and HClO are formed in solution H⁺ ions. Equilibrium of that reaction can be displaced to the right at binding the H⁺ ions. To perform it in the most simple way into solution are added some alkali, then it gives:

Cl₂ + H₂O HCl + HClO

HCl + HClO + 2KOH = KCl + KClO + 2H₂O

or, in general case:

2KOH + Cl₂ = KCl + KClO + H₂O

Solution which is formed in this case is named Javel water. This reaction proceeds on cold.

The hypochlorite and chloride solution obtained in this way is used for bleaching. Its bleaching properties are due to the fact that potassium hypochlorite readily decomposes when acted upon the carbon dioxide contained in air, hypochlorous acid being formed:

KOCl+CO₂+H₂O = KHCO₃+HOC1

It is this acid that bleaches pigments by oxidizing them.

A similar solution containing sodium hypochlorite is obtained when chlorine is passed into a sodium hydroxide solution. Both solutions can be prepared by the electrolysis of potassium or sodium chloride solutions if the evolving chlorine is allowed to react with the alkalis formed during electrolysis.

When chorine reacts with dry slaked lime, lime chloride or chlorinated lime is obtained. The high-quality sorts of chloride lime approximately correspond to the composition 3Ca(OCl)Cl^.СаCl₂^.nH₂O and contain up to 35% of active chlorine (“active chlorine” is that which is formed at action of HCl). Its main constituent part is the CaOCl₂ salt formed according to the equation:

Ca(OH) ₂ + Cl₂ = CaOCl₂ + H₂O

This salt, which is often written in the form of CaCl(OCl), has the structural formula Ca , according to which it should be considered as a mixed salt of hydrochloric and hypochlorous acids.

Chlorinated lime is a white powder with a sharp smell. It has strong oxidizing properties. In humid air, it gradually decomposes under the action of carbon dioxide, liberating hypochlorous acid:

2CaOCl₂ + CO₂ + H₂O = CaCO₃ + CaCl₂+ 2HOC1

When chlorinated lime is reacted with hydrochloric acid, chlorine is evolved:

CaOCl₂+ 2HC1 = CaCl₂+ CI₂+ H₂O

Chlorinated lime is used for bleaching vegetable fibres (fabrics, paper), and for disinfection.

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