UNIT# 14
SULPHUR AND ITS
COMPOUNDS
|
Q# |
Question |
Year |
|
Q# 01 |
Describe the industrial manufacture of Sulphuric acid
by contact process with balanced chemical equations |
[2018][2016][2013] |
|
Q# 02 |
Write
Uses of sulphuric acid |
[2009][2012] |
|
Q# 03 |
Describe crystalline and amorphous forms of
Sulphur |
[2012] [2010] |
|
Q# 04 |
Extraction
of Sulphur by Frasch process |
[2016]
[2014] [2011] [2010] |
|
Q# 05 |
Describe three allotropic forms of Sulphur. |
[2018] |
|
Q# 06 |
What
is allotropy? |
[2018][2017][2016][2010][2012][2009]
[2005] |
Q. Write note on Sulphur.
SULPHUR
It is the second member of
the group VI A and has symbol ‘S’. Its atomic number is 16 and atomic mass is
32. Sulphur has been known for the medicinal and geometrical affect from very
ancient time before 100 B.C’s but its chemical nature remained unknown.
OCCURRENCE
1. It occurs free in nature
wherever there has been volcanic activity.
2. It is non-metallic element.
COMBINED
STATE
In combined state, sulphur is
found mostly in the form of Sulphides and sulphates
PLANTS
AND ANIMALS
Sulphur is essential
constituent of many organic substances of plants and animals origins e.g.
onion, garlic and protein
FOSSILS
FUEL
Coal, natural gas and
petroleum also contains sulphur compounds e.g. natural gas contains hydrogen
sulphide (H2S) which is a poisonous gas
Q. Define Allotropy.
ALLOTROPY
The existence of an element
in two or more different forms in the same state of matter is called allotropy
e.g. solid, liquid and gaseous sulphur.
Q. Describe various allotropic
forms of Sulphur.
ALLOTROPIC
FORMS OF SULPHUR
Sulphur exists in several
allotropic forms. Three important forms of sulphur are
1. Rhombic sulphur [α sulphur]
2. Monoclinic sulphur [β sulphur]
3. Plastic sulphur [γ
sulphur]
Q. Describe structure of Rhombic
Sulphur and its physical properties.
STRUCTURE
OF RHOMBIC SULPHUR
Rhombic sulphur consists of S8
molecule. These molecules consist of 8 sulphur atoms bound to each other
through single covalent bond. The shape of rhombic sulphur is octahedral.
PHYSICAL
PROPERTIES OF RHOMBIC SULPHUR
1. Free sulphur exists in nature
as rhombic sulphur.
2. It is the most stable
crystalline form of sulphur at ordinary condition.
3. Its color is pale yellow.
4. Its melting point is 1130
C.
5. Its density is 2.08 gcm3
at 200 C.
Q. Describe structure of
Monoclinic Sulphur and its physical properties.
STRUCTURE
OF MONOCLINIC SULPHUR
Monoclinic sulphur also consists
of S8 molecule like Rhombic sulphur. The only difference in
structure in the shape of the crystals. Molecules unite together to give long
needle shaped crystals.
PHYSICAL
PROPERTIES OF SULPHUR
1. It is stable between 960
C and 1190 C.
2. Its melting point is 1190
C.
3. Its density is 1.96 gm/ cm3.
4. Its color is dark yellow.
5. It is insoluble in water.
Q. Describe structure of Plastic
Sulphur and its physical properties.
STRUCUTRE
OF PLASTIC SULPHUR
Plastic sulphur is a rubber
like mass. It looks like it is made of plastic. Plastic sulphur is generally
not considered to be a true allotrope of sulphur because it is unstable and
changes to rhombic sulphur on standing. It has zig-zag arrangement of sulphur
atoms.
PROPERTIES
OF PLASTIC SULPHUR
1. Plastic sulphur is usually
black but the pure form is pale yellow.
2. It is non crystalline,
amorphous, allotrope of sulphur.
3. It is elastic and can be
stretched like rubber.
4. It is insoluble in water.
Q. Describe structure of Plastic
Sulphur and its physical properties.
Production -The Frasch Process
In this process, 99.99% pure
Sulphur can be obtained.
Mostly sulphur containing
minerals are metal sulphides in which the best known is Pyrite (CuFeS2).
The Frasch process is based on the fact that sulfur has a comparatively low melting
point.
In this process, 99.9% pure
Sulphur can be eliminated out by using hot water and air. Superheated water is
entered into the outermost of the three concentric pipes. Compressed air is pumped down
the center tube, and a mixture of elemental sulfur, hot water, and air comes up
the middle pipe. Sulfur is melted with superheated water (at 170 °C under high
pressure) and forced to the surface of the earth as slurry.
Q. Describe physical properties
of Sulphur.
PHYSICAL
PROPERTIES OF SULPHUR
1. It is yellow solid
2. It is bad conductor of heat
and electricity
3. It boils at 4440C
4. It melts between 1130C
and 1190C
Q. Describe chemical properties
of Sulphur.
CHEMICAL
PROPERTIES OF SULPHUR
1) Reaction with metals
Sulphur combines directly
with many metals to form sulphide when heated in the absence of air
2Cu + S ® Cu2S [Cuprous
sulphide]
Fe + S ® FeS [Ferrous sulphate
Zn + S ® ZnS [Zinc sulphide]
Pb + S ® PbS [Lead sulphide]
2Na + S ® Na2S [Sodium
Sulphide]
2) Reaction with non metals
S + O2 ® SO2
H2 + S ® H2S
C + 2S ® CS2
2S + Cl2 ® S2Cl2
S + 3F2 ® SF6
3)
Reactions with acids
S + 2H2SO4
(conc) ® 3SO2 + 2H2O
S + 6HNO3 (conc) ® H2SO4
+ 6NO2 + 2H2O
Q. Describe uses of Sulphur.
USES
OF SULPHUR
1. It is used in the preparation
of sulphur dyes
2. It is used in making calcium
and magnesium hydrogen sulphates which are used for bleaching and pulp
3. It is used to make SO2
, CS2 and H2 mainly for the production of H2SO4
4. It is used in the
vulcanization rubber for making tires
5. Some of its products are used
as fungicides and insecticides
6. It is used in the manufacture
of explosive, fireworks, gun powder and matches etc.
7.
Sulfur is mostly used for the
production of sulfuric acid, H2SO4
Q. Describe contact Process.
CONTACT PROCESS [PRODUCTION
OF H2SO4]
Sulfuric acid (H2SO4)
is a highly corrosive strong mineral acid. On the large scale, H2SO4
is prepared by Contact Process. The process can be divided into following five
stages:
1. Production of sulphur dioxide
2. Purification of Sulphur di
oxide
3. Oxidation of Sulphur di oxide
4. Production of Oleum
5. Production of Sulphuric acid
PRODUCTION OF SO2
By burning Sulphur in excess of air, Sulphur di oxide
can by produced:
S + O2 ⟶ SO2
Another method of SO2 production is heating
sulphide ore [pyrite] in excess of air:
4FeS2 + 11 O2 ⟶ 2Fe2O3 + 8SO2
PURIFICATION OF SO2
The mixture of SO2 and air is passed through
special dust chambers or filters to make the mixture free from all sorts of
impurities.
CONVERSION OF SO2 INTO SO3
In this stage, SO2 is treated with the free O2.
It is reversible, exothermic reaction.
2SO2 + O2 ⟶ 2SO3 ∆H = -196 KJ/mol
As the
reaction is exothermic, so the formation of SO3 will be favored by
following conditions, according to Le Chatlier principle.
·
Low temperature
·
High pressure
PRODUCTION OF OLEUM
In this stage, SO3 is treated with
concentrated H2SO4 to produce Oleum (H2S2O7).
Remember, SO3 cannot be treated with water, because it may result in
uncontrollable reaction.
H2SO4 + SO3 ⟶ H2S2O7
(Oleum)
PRODUCTION OF H2SO4
H2SO4 can be safely reacting with
water to produce concentrated Sulphuric acid.
H2S2O7 + H2O ⟶ 2H2SO4
Q. Describe uses of Sulphuric
acid.
USES OF SULPHURIC ACID
·
It is used in the production of fertilizers.
·
It is widely used in the manufacturing of
various chemicals.
·
It is used in petroleum refining.
·
It is used in processing metals.
·
It acts as electrolyte in lead storage battery.
Q. Describe physical properties
of Sulphuric acid.
PHYSICAL
PROPERTIES OF SULPHURIC ACID
1. It is colorless, odorless
heavy oily liquid known as oil of vitriol
2. It is sour in taste
3. Its dilute solution turns
blue litmus paper to red
4. Its melting point is 10.50
C and its boiling point is 3380 C
5. It conduct electricity
Q. Describe chemical properties
of Sulphuric acid.
CHEMICAL
PROPERTIES OF H2SO4
1) Ionization
in water
H2SO4 +
H2O ® H3O + HSO4-1
HSO4-1
+ H2O ® H3O + SO4-1
2) Reaction
with metals
Dilute H2SO4
reacts with metals to produce hydrogen gas
Zn + H2SO4
® ZnSO4 + H2
Fe + H2SO4 ® FeSO4 + H2
2Al + 3H2SO4 ® Al2(SO4)3+
3H2
Cu + 2H2SO4 ® CuSO4
+ SO2 + 2H2O
Pb + 2H2SO4 ® PbSO4
+ SO2 + 2H2O
2Al + 6H2SO4 ® Al2(SO4)3
+ 3SO2 + 2H2O
3) Oxidation
of Non Metals
Concentrated sulphuric acid
oxidizes non metals
C + 2H2SO4
® CO2 + 2SO2 + 2H2O
S + 2H2SO4 ® 3SO2
+ 2H2O
2P + 3H2SO4
® 2H3PO4
+ 3SO2
H2S + H2SO4 ® S + SO2 + 2H2O
2HI + H2SO4 ® I2 + SO2 + 2H2O
4) Dehydrating
Agent
The removal of water from
compound is called dehydration. Sulphuric acid; in such a way is a strong
dehydrating agent.
C12H22O11 ® 12C
+ 11H2O
CH3-CH2-OH ® CH2
= CH2 + H2O
HCOOH ® CO
+ H2O
COOH-COOH ® CO
+ CO2 + H2O
CuSO4.5H2O ® CuSO4 + 5H2O
Choose the correct option for
each of the following statement.
i.
The formula of iron pyrite
is:
a. FeS
b. FeS2
c. Fe2S3
d. Fe2S2
ii.
Sulphur burns in oxygen with
blue flame to produce:
a. SO3
b. SO2
c. S2Cl2
d. H2S
iii.
The non-crystalline form of
Sulphur is:
a. Plastic sulphur
b. Rhombic sulphur
c. Monoclinic sulphur
d. Ordinary sulphur
iv.
The most stable form of
sulphur is:
a. Plastic sulphur
b. Rhombic sulphur
c. Monoclinic sulphur
d. Ordinary sulphur
v.
Sulphuric acid is used in:
a. Batteries
b. Fertilizers
c. Paints and pigments
d. All of the above
vi.
On a large scale, Pure
sulphuric acid is prepared from:
a. Contact process
b. Ostwald’s method
c. Castner Kellner cell
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