5th Lecture on Elements of groups 16, 17 & 18 Chemistry Part I12th Standard by Rizwana Mohammed

1. The Malegaon High School & Jr. College
Malegaon, (Nashik), 423203
5th Lecture on Elements of
groups 16, 17 & 18
Chemistry Part I, 12th Science
By
Rizwana Mohammad

2. Chlorine and compounds of chlorine:
Chlorine: (Greek, chloros = greenish yellow)
a. Preparation:
1. Chlorine can be prepared by the oxidation of HCl with any of
following oxidising agents.
i. Manganese dioxide:
MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O
ii. Potassium permanganate:
2KMnO4 + 16HCl → 2KCl + 2MnCl2 + 8H2O + 5Cl2
2. Chlorine can also be prepared by the action of conc. H2SO4 on a
mixture of NaCl and MnO2.
4NaCl + 4H2SO4 → 4NaHSO4 + 4HCl
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
4NaCl + MnO2 + 4H2SO4 → 4NaHSO4 + MnCl2 + 2H2O + Cl2

3. b. Manufacture of chlorine:
i. Deacon’s process:
4HCl + O2 2Cl2 + 2H2O
ii. Electrolytic process:
By the electrolysis of brine, chlorine is liberated at the anode.
NaCl ⇌ Na+ + Cl-
Cathod: 2H2O + 2e- → H2 + 2OH-
Na+ + OH- → NaOH
Anode: Cl- → Cl + e-
Cl + Cl → Cl2
c. Physical properties of chlorine:
i. Chlorine is a greenish yellow gas having pungent and suffocating
odour.
ii. It is poisonous in nature.
iii. It can be easily liquify into a greenish yellow liquid, which boils at
293K.
iv. It dissolves in water to give chlorine water.
v. It is 2-5 times heavier than air.
C Clu 2
723K

4. d. Chemical properties of chlorine:
i. Reaction with metals:
2Al + 3Cl2 → 2AlCl3
2Na + Cl2 → 2NaCl
2Fe + 3Cl2 → 2FeCl3
ii. Reaction with nonmetals:
P4 + 6Cl2 → 4PCl3
S8 + 4Cl2 → 4S2Cl2
iii. Affinity for hydrogen:
H2 + Cl2 → 2HCl
H2S + Cl2 → 2HCl + S
iv. Reaction with NH3:
8NH3 + 3Cl2 → 6NH4Cl + N2
Excess
NH3 + 3Cl2 → NaCl3 + 3HCl
Excess

5. v. Reaction with alkali:
2NaOH + Cl2 → NaCl + NaOCl + H2O
Cold and dilute
6NaOH + 3Cl2 → 5NaCl + NaClO3 + 3H2O
Hot and conc.
2Ca(OH)2 + 2Cl2 → Ca(OCl)2 + CaCl2 + 2H2O
Slaked lime
vi. Reaction with hydrocarbon:
CH4 + Cl2
UV
CH3Cl + HCl
H2C = CH2 + Cl2 →
vii. Oxidising property:
2FeSO4 + H2SO4 + Cl2 → Fe2(SO4)3 + 2HCl
Na2SO3 + Cl2 + H2O → Na2SO4 + 2HCl
SO2 + 2H2O + Cl2 → H2SO4 + 2HCl
I2 + 6H2O + 5Cl2 → 2HIO3 + 10HCl
Cl Cl
1,2 - Dichloroethane

6. viii. Bleaching property:
• Chlorine requires the presence of moisture for bleaching.
• It liberates nascent oxygen from water which is responsible for its
oxidising and bleaching property.
Cl2 + H2O → HCl + HOCl
HOCl → HCl + [O]
• Chlorine bleaches vegetable matter or coloured organic matter in
the presence of moisture to colourless matter.
• Coloured organic matter + [O] → colourless organic matter.

7. e. Uses: Chlorine is used
• For purification (sterilizing) of drinking water.
• For bleaching wood pulp required for manufacture of paper and
rayon, bleaching cotton and textiles.
• For extraction of metals like gold and platinum.
• In the manufacture of dyes, drugs and organic compounds such as
CCl4, CHCl3, DDT, refrigerants etc.
• In the preparation of poisonous gases such as phosgene (COCl2),
tear gas (CCL3NO2), mustard gas (ClCH2CH2SCH2CH2Cl).

8. Hydrogen chloride:
a. Preparation:
NaCl + H2SO4
420K
NaHSO4 + HCl
NaHSO4 + NaCl
420K
Na2SO4 + HCl
b. Physical properties of HCl:
i. HCl is a colourless and pungent smelling gas.
ii. It can be easily liquefied to a colourless liquid (b.p. 189K) which
freezes to a white crystalline solid (m.p. 159K).
iii. It is highly soluble in water.

9. c. Chemical properties:
i. Acidic property:
HCl is highly soluble in water and ionizes as follows:
HCl(g) + H2O(l) → H3O+
(aq) + Cl-
(aq)
Ka = 107
The aqueous solution of HCl gas is called hydrochloric acid. High value
of dissociation constant (Ka) indicates that it is a strong acid in water.
ii. Reaction with NH3:
NH3 + HCl → NH4Cl
white fumes
iii. Reaction with noble metals:
Au + 4H+ + NO3
- + 4Cl-→ AuCl4
- + NO + 2H2O
3Pt + 16H+ + 4NO3
- + 18Cl- → 3PtCl6
2- + 4NO + 8H2O