SS2 Chemistry Lesson Note on Preparation and Properties of Chlorine

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TOPIC: HALOGENS

CONTENT:

1. PREPARATION OF CHLORINE (LABORATORY AND INDUSTRIAL)
2. PROPERTIES OF CHLORINE (PHYSICAL AND CHEMICAL)
3. HYDROGEN CHLORIDE GAS: LABORATORY PREPARATION PROPERTIES AND USES,
4. TEST FOR HCL GAS AND FOUNTAIN EXPERIMENT.

PERIOD1: PREPARATION OF CHLORINE (LABORATORY AND INDUSTRIAL)

In the laboratory, chlorine is prepared by the oxidation of concentrated hydrochloric acid with manganese (IV) oxide. The mixture is heated to obtain a greenish-yellow gas (chlorine).

MnO_2(s) + 4HCl _(aq) →  MnCl_2(aq) + 2H₂O + Cl₂

Chlorine is prepared industrially by the electrolysis of brine and molten metallic chlorides

EVALUATION

Describe the laboratory preparation of chlorine

PERIOD 2: PHYSICAL PROPERTIES OF CHLORINE

1. It is a greenish-yellow gas with an unpleasant choking smell.
2. It is denser than air.
3. It is slightly soluble in water.
4. It is poisonous.

The chemical properties of chlorine have been discussed under the general properties of halogens. Let’s discuss the oxidizing properties of chlorine.

1. Chlorine oxidizes hydrogen sulphide to yellow sulphur.

Cl₂  +  H₂S   →   2HCl  +  S

2. Bleaching property of chlorine

Chlorine bleaches by oxidation. When chlorine dissolves in water, it forms hydrochloric acid and oxochlorate (i) acid (chlorine water).

Cl₂ +  H₂O    →   HCl  +  HOCl

In bleaching oxochlorate (i) acid gives out oxygen atom. The oxygen atom then bleach the material by oxidation. This bleaching action is permanent because the material cannot be re-oxidize by atmospheric oxygen.

EVALUATION:

1. State four physical properties of chlorine.
2. Describe the bleaching action of chlorine.

PERIOD 3: HYDROGEN CHLORIDE GAS PREPARATION, PROPERTIES AND USES.

Hydrogen chloride is prepared in the laboratory by the action of concentrated tetraoxosuphate (vi) acid on sodium chloride. The gas is dried by passing it through concentrated tetraoxosulphate (vi) acid and collected by downward displacement of air.

NaCl_(s)  +  H₂SO_4(aq)  →   Na₂SO_4(aq)  +  HCl_(g).

Dissolution of hydrogen chloride in water gives hydrochloric acid.

PHYSICAL PROPERTIES OF HYDROGEN CHLORIDE

1. It is a colourless gas with sharp irritating smell.
2. It is denser than air.
3. It is very soluble in water.
4. It turns moist blue litmus paper red.
5. It is soluble in non-polar solvent like methylbenzene. Its solution in methylbenzene cannot conduct electricity because it does not undergo ionization when dissolved in methylbenzene. But when dissolved in water, it undergoes ionization and so conduct electricity because of the presence of free mobile ions.

CHEMICAL PROPERTIES OF HYDROGEN CHLORIDE

1. It reacts with active metals to liberate hydrogen gas e.g

Zn_(s)   +  2HCl_(g)   →  ZnCl_2(s)  +  H_2(g)

2. It reacts with ammonia to form a dense white fume of ammonium chloride.

HCl_(g)  +  NH_3(g)  →  NH₄Cl_(s)

3. Hydrochloric acid (obtained when hydrogen chloride dissolved in water) reacts with metallic trioxocarbonate (iv) or metallic hydrogentrioxocarbonate (iv) to liberate carbon (iv) oxide.

2HCl_(aq)  +  Na₂CO_3(s)  → 2NaCl_(aq) +  H₂O_(l)  +  CO_2(g)

4. Hydrochloric acid (obtained when hydrogen chloride dissolved in water) precipitates silver chloride from solution.

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