4th 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
4th Lecture on Elements of
groups 16, 17 & 18
Chemistry Part I, 12th Science
By
Rizwana Mohammad

2. Compounds of sulphur:
Sulphur dioxide:
a. Preparation:
i. From sulphur:
S(s) + O2(g) → SO2(g)
ii. From sulphite:
Na2SO3 + H2SO4(aq) → Na2SO4 + H2O(l) + SO2(g)
iii. From sulphides: (Industrial method)
2ZnS(s) + 3O2(g) ՜
Δ
2ZnO(s) + 2SO2(g)
4FeS2(s) + 11O2(g) ՜
Δ
2Fe2O3(s) + 8SO2(g)
b. Physical properties of SO2:
i. It is a colourless gas with a pungent smell.
ii. It is poisonous in nature.
iii. It is highly soluble in water and its solution in water is called
sulphurous acid.
iv. It liquefies at room temperature under a pressure of 2 atm and
boils at 263K.

3. c. Chemical properties:
i. Reaction with Cl2:
SO2(g) + Cl2(g)
charcoal
SO2Cl2(l)
ii. Reaction with O2:
2SO2(g) + O2(g)
V2O5
2SO3(g)
iii. Reaction with NaOH:
2NaOH + SO2 → Na2SO3 + H2O
iv. Reaction with Na2SO3:
Na2SO3 + H2O(l) + SO2 → 2NaHSO3
v. Reducing property:
SO2 acts as a reducing agent in the presence of moisture.
• Moist SO2 reduces ferric salts into ferrous salts.
2Fe3+ + SO2 + 2H2O → 2Fe2+ + SO4
-2 + 4H+
• Moist SO2 decolourises acidified potassium permangnate (VII) solution.
2KMnO4 + 5SO2 + 2H2O → K2SO4 + 2MnSO4 + 2H2SO4
• Moist SO2 reduces halogens to halogen acids.
I2 + SO2 + 2H2O → H2SO4 + 2HI

4. d. Structure of SO2:
SO2 is angular with O-O-O bond angle of 119.5°
The S-O double bond arises from dπ-pπ bonding. It is a resonance hybrid of
two canonical forms.
e. Uses: SO2 is used
i. In refining of petroleum and sugar.
ii. In bleaching of wool and silk.
iii. As an anti-colour, disinfectant.
iv. As a preservative.
v. In the manufacture of H2SO4, NaHSO3, a number of organic and inorganic
chemicals.

5. Sulphuric acid, H2SO4:
a. Preparation:
Sulphuric acid is manufactured by contact process, which involves the
following three steps.
i. S(s) + O2(g) ՜
Δ
SO2(g)
4FeS2(s) + 11O2(g) ՜
Δ
2Fe2O3(s) + 8SO2(g)
ii. 2SO2(g) + O2
V2O5
2SO3(g)
Low temperature (720K) and high pressure (2 bar) are favourable conditions
for maximum yield of SO3.
iii. SO3(g) + H2SO4 → H2S2O7
oleum
H2S2O7 + H2O → 2H2SO4

6. b. Physical properties of H2SO4:
i. Sulphuric acid is a colourless, dense, oily liquid.
ii. It has a density (specific gravity) of 1.84 g/cm3 at 298K.
iii. It freezes at 283K and boils at 611K.
iv. It is highly corrosive and produces severe burns on the skin.
c. Chemical properties:
i. Acidic property:
H2SO4(aq) + H2O(l) → H3O+
(aq) + HSO4
-
(aq) Ka > 10
HSO4
-
(aq) + H2O(l) → H3O+
(aq) + SO4
-2
(aq) Ka = 1.2 X 10-2
The greater value of Ka (Ka > 10) means that H2SO4 is largely
dissociated into H+ and HSO-
4 ions. Thus H2SO4 is a strong acid.
ii. Reaction with metals and nonmetals (oxidising property):
Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O
conc.
S + 2H2SO4 → 3SO2 + 2H2O
conc.
C + 2H2SO4 → CO2 + 2SO2 + 2H2O
conc.

7. iii. Dehydrating property:
Concentrated sulphuric acid is a strong dehydrating agent.
Sulphuric acid removes water from sugar and carbohydrates. Carbon
left behind is called sugar charcoal and the process is called charring.
C12H22O11
conc. H2SO4
12C + 11H2O
iv. Reaction with salts:
NaCl + H2SO4 → NaHSO4 + HCl
KNO3 + H2SO4 → KHSO4 + HNO3
CaF2 + H2SO4 → CaSO4 + 2HF

8. d. Uses:
Sulphuric acid is a very important industrial chemical. It is used.
• In the manufacture of fertilizers.
e.g. ammonium sulphate, superphosphate etc.
• In the manufacture of pigments, paints and dyestuff intermediates.
• In petroleum refining.
• In detergent industry.
• In metallurgy, for cleaning of metals, electroplating and galvanising.
• In storage batteries.
• As a laboratory reagent.
• In the manufacture of nitrocellulose products.