UNIT# 15
HALOGENS
|
Q# |
Question |
Year |
|
Q# 01 |
Define halogen. |
[2017] |
|
Q# 02 |
Write
three uses of Chlorine. |
[2013] |
|
Q# 03 |
Explain laboratory method of preparation of
Chlorine. |
[2017][2015][2012] [2010] |
|
Q# 04 |
Explain
the laboratory method of preparation of HCl. |
[2015] |
|
Q# 05 |
Write note on Bleaching powder. |
[2014] [2012] |
|
Q# 06 |
Write
chemical equation of reaction of HCl with the following ·
Sodium hydroxide ·
Sodium bi carbonate ·
Manganese di oxide |
[2014] |
|
Q# 07 |
Describe Chlorination of methane. |
[2014] |
Q. What do you know about
Halogens?
HALOGEN
Halogen
is the VII group of periodic table which includes five natural and one
artificial created elements which are Florine (F), Chlorine (Cl), Bromine (Br),
Iodine (I), Astatine (At) and Tennessine (Ts). The symbol X is often
used generically to refer to any halogen.
The
term Halogen means ‘salt formers’ or ‘salt producing’ as halogens react with
metals to produce wide range of salts including Calcium fluoride, sodium
chloride (table salt), silver bromide, potassium iodide.
Q. Describe the laboratory method
of preparation of chlorine.
LABORATORY
METHOD OF PREPARATION OF CHLORINE
The laboratory method of
preparation of Chlorine (Cl2) was proposed by Scheele. In this method, the chlorine is produced by
the reaction of Hydrochloric acid (HCl) with Manganese Dioxide (MnO2).
4HCl + MnO2 ® MnCl2 + 2H2O + Cl2
When
concentrated HCl is gently heated with oxidizing agent, such as MnO2.
KMnO4, chlorine gas is produced.
2KMnO4
+ 16HCl ® 2KCl +
2MnCl2 + 8H2O + 5Cl2
PROCEDURE
A
small amount of MnO2 is taken in the round bottom flask, placed on a
tripod stand, fitted with double hole cork. From the one end of the cork, a
delivery tube is passed to connect the flask with the gas jar while from another
end thistle funnel is inserted. Concentrated hydrochloric acid is added in the
flask through funnel with the gentle heating. Greenish yellow gas starts to
produce which is collected in the gas jar by the upward displacement.
2NaCl
+ 2H2SO4 + MnO2 ® Na2SO4 + MnSO4 + 2H2O
+ Cl2
Another
method for the production of Chlorine is heating Sodium chloride with
concentrated sulphuric acid in the presence of catalyst (MnO2)
2NaCl
+ 2H2SO4 + MnO2 ® Na2SO4
+ MnSO4 + 2H2O + Cl2
Q. Describe the industrial method of preparation of
chlorine.
INDUSTRIAL
METHOD OF PREPARATION OF CHLORINE
Following
are the two methods of industrial or commercial preparation of Chlorine.
o
Nelson’s cell
o
Castner Kellner Cell
NELSON’S
CELL
Nelson’s
cell consisted of a cathode which is U-shaped steel vessel and the graphite
anode; dipped in the salt solution. Asbestos layer is the separation between
cathode and anode.
On
passing electric current across the salt solution, chlorine gas produced at
anode while the sodium metal is produced at cathode which contacts with H2O
and results in the formation of sodium hydroxide along with the liberation of
Hydrogen gas.
Ionization
reaction
2NaCl
⟶ 2Na+ + 2Cl-
AT
ANODE
2Cl-
⟶ Cl2 +
2e-
AT CATHODE
2Na+ + 2e-
⟶ 2Na
2Na+ + 2H2O
⟶ 2NaOH + H2
CASTNER
KELLNER CELL [Production of Chlorine Gas]
In Castner Kellner cell, the
anodes are the titanium plates which are dipped in the salt solution while the
cathode consists of moving mercury layer. As the upper cell is slightly tilt so
the mercury flows in from right to left. There is another chamber called
‘denuder’ or ‘Soda cell’ which is packed with graphite blocks.
On passing electric current,
the Chlorine gas liberated and collected at anode. Sodium metal which is
produced at cathode reacts with mercury and ultimately forms the sodium
amalgam.
Chemical
equations for production of Chlorine
2NaCl ® 2Na+ + 2Cl-
AT ANODE
2Cl-
® Cl2 + 2e-
AT CATHODE
2Na+
+ 2e- ® 2Na
2Na + 2Hg ® 2NaHg
[Sodium Amalgam]
Sodium
Amalgam is then carried to denuder and allowed with water to react with water
to produce NaOH along with the liberation of Hydrogen gas.
2NaHg + 2H2O
® 2NaOH
+ H2 + 2Hg
Q. Describe the advantages and
disadvantages of Castner Kellner Cell.
ADVANTAGES
OF CASNTER KELLNER CELL
·
Obtained NaOH is
highly pure
·
Process is very
efficient
·
Possible reaction
between NaOH and Cl2 is avoided because NaOH is obtained in
separated chamber
DISADVANTAGES OF CASTNER KELLNER CELL
As there are
many advantages of Castner Kellner cell, there are also some disadvantages
which are mentioned below:
·
Environmental
pollution due to escape of Hg vapors
·
It consumes high amount of electricity
Q. Describe the physical
properties of Chlorine gas.
PHYSICAL
PROPERTIES OF CHLORINE GAS
1. It is a poisonous and toxic
gas.
2. It is greenish yellow, pungent
smell gas.
3. Small amount of Chlorine gas
if inhaled causes sore throat and running eyes.
4. Large amount of Chlorine gas
if inhaled may case cough, lung damage and ultimately leads to death.
5. It is soluble in water
6. Its density is 3.214 gm/cm3
7. It boils at -340 C
and melts at -1010C
8. Its electro negativity is 3.0
Q. Describe the chemical
properties of Chlorine gas.
CHEMICAL
PROPERTIES OF CHLORINE
Chlorine
is a reactive element which combines with other elements to form Chlorides.
1) Reaction
with Hydrogen
H2
+ Cl2 ⟶ 2HCl
2) Reaction
with Metals
2Na
+ Cl2 ⟶ 2NaCl
Zn + Cl2 ⟶ ZnCl2
2Sb + 3Cl2 ⟶ 2SbCl3
2 Fe + 3Cl2 ⟶ 2FeCl3
Sn + 2Cl2 ⟶ SnCl4
3) Reaction
with non-metals
2P + 3Cl2 ⟶ 2PCl3
2P + 5 Cl2 ⟶ 2PCl5
2S + Cl2 ⟶ S2Cl2
4) Addition
Reaction
Chlorine directly combines
with many compounds to form addition products.
CH2 = CH2
+ Cl2 ⟶ CH2Cl-CH2Cl
CO + Cl2 ⟶ COCl2
SO2 + Cl2
⟶ SO2Cl2
5) Substitution
Reaction
Chlorine reacts with many
compounds and substitute one or more atom.
H2S + Cl2 ⟶ 2HCl + S
2KBr + Cl2 ⟶ 2KCl + Br2
2KI + Cl2 ⟶ 2KCl + I2
CH4 + Cl2
⟶ CH3Cl + HCl
CH3Cl + Cl2
⟶ CH2Cl2 + HCl
CH2Cl2
+ Cl2 ⟶ CHCl3 + HCl
CHCl3 + Cl2
⟶ CCl4 + HCl
6) Reaction
with ammonia
2NH3 + 3Cl2
⟶ N2 + 6HCl
6NH3 + 6HCl ⟶ 6NH4Cl
7) Reaction
with lime water
2 Ca(OH)2 + 2Cl2
⟶ Ca(OCl)2 + CaCl2 + 2H2O
6 Ca(OH)2 + 6Cl2 ⟶ Ca(ClO3)2 + 5 CaCl2 + 6H2O
Ca(OH)2 + Cl2
⟶ Ca(OCl)Cl + 2H2O
8) Oxidation
Reaction
Cl20 +
H2O ⟶ H-Cl + HOCl
2FeCl2 + Cl2
⟶ 2FeCl3
H2SO3 +
Cl2 + H2O ⟶ H2SO4 +
2HCl
Cl2 + H2O ⟶ HCl + HOCl
HClO ⟶ HCl + [O]
H2SO3 +
[O] ⟶ H2SO4
9) Reaction
with Alkalis
Cl2 + 2NaOH ⟶ NaCl + NaClO + H2O
3Cl2 + 6NaOH ⟶ 5NaCl + NaClO3 + 3H2O
3NaClO ⟶ NaClO + 2NaCl
Q. Describe the uses of Chlorine
gas.
USES
OF CHLORINE
·
Chlorine is commonly used as an antiseptic
·
Chlorine is used to make drinking water safe and
sterilization of drinking water
·
It is used in the production of dyes, drugs and
explosives etc
·
It is used in the layer test for identification
of other halogens
·
It is used to treat swimming pools.
·
Large amounts of chlorine are used in many
industrial processes, such as in the production of paper products, plastics,
dyes, textiles, medicines, antiseptics, insecticides, solvents and paints.
·
Two of the most familiar chlorine compounds are
sodium chloride (NaCl) and hydrogen chloride (HCl). Sodium chloride, commonly
known as table salt, is used to season food and in some industrial processes.
Hydrogen chloride, when mixed with water (H2O), forms hydrochloric
acid, a strong and commercially important acid.
Q. Describe the laboratory
preparation of Hydrochloric acid?
LABORATORY METHOD OF
PREPARATION OF HYDROCHLORIC ACID
In this method, sodium
chloride (NaCl) is added in a Round bottom flask, placed over tripod stand to
ensure the proper heating, if needed. Round bottom flask is sealed with double
hole cork from which one end thistle funnel is crossed while from other delivery
tube is attached to make the connection of the flask with the gas jar.
As soon as concentrated
Sulphuric acid is added through thistle funnel the reaction starts at once to
produce Hydrochloric acid gas which is collected in the jar by the upward displacement
of air.
The reaction can be
illustrated as:
NaCl + H2SO4 ⟶ NaHSO4 + HCl
Q. Describe the industrial
preparation of Hydrochloric acid?
INDUSTRIAL METHOD OF HCl
METHOD # 01
Industrially, the
Hydrochloric acid is prepared simply by the direct combination of H2
and Chlorine gas.
H2 + Cl2 → 2HCl ∆H
= -44.12 KJ/ mol
METHOD # 02
By the hydrolysis of certain
reactive chloride compounds like phosphorous chloride, thinly chloride (SOCl2),
acyl chlorides, HCl can also be produced.
PCl5 + H2O
→ POCl3 +
2 HCl
METHOD # 03
By the reaction of Chlorine
with hydrogen compound also results in the formation of Hydrochloric acid.
H2S + Cl2 → 2HCl + S
2Cl2 + 2H2O → 4HCl + O2
Q. Describe the physical
properties of Hydrochloric acid?
PHYSICAL
PROPERTIES OF HYDROCHLORIC ACID
·
It is colorless gas
·
It has acidic taste
·
Highly soluble in
water
·
Slightly heavier than
air
Q. Describe the chemical
properties of Hydrochloric acid?
CHEMICAL
PROPERTIES OF HYDROCHLORIC ACID
1)
Reaction with water
HCl
+ H2O ⟶ H3O+
+ Cl-
2) Reaction with alkalis
HCl
produces salt and water when reacts with alkalis.
NaOH
+ HCl ⟶ NaCl + H2O
KOH
+ HCl ⟶ KCl + H2O
3)
Reaction with ammonia
HCl
react with ammonia to produce ammonium chloride.
NH3
+ HCl ⟶ NH4Cl
4)
Reaction with metal carbonates and bi
carbonates
Na2CO3
+ 2HCl ⟶ 2NaCl +
CO2 + H2O
CaCO3
+ 2HCl ⟶ CaCl2
+ CO2 + H2O
NaHCO3
+ HCl ⟶ NaCl +
CO2 + H2O
5)
Reaction with AgNO3
AgNO3
+ HCl ⟶ AgCl +
HNO3
6)
Reaction with Pb(NO3)2
Pb(NO3)2
+ 2HCl ⟶ PbCl2 + 2HNO3
Q. Describe the uses of
Hydrochloric acid.
USES
OF HYDROCHLORIC ACID
·
It is used to remove
rust from iron
·
It is used as
chemical reagent
·
It is used in the
manufactures of dyes, plastics, medicines, rubber etc
·
It is used to clean
wares and roofs
·
It is used in the
pickling of iron
Q. What is Bleaching powder?
BLEACHING
POWDER
Bleaching
powder is the mixture of Calcium with chloride and oxychloride. Professor
Odling suggested the chemical formula of Bleaching powder (CaOCl2).
LABORATORY
PREPARATION OF BLEACHING POWDER
In
the laboratory, bleaching powder is prepared by shaking a small quantity of
slaked lime Ca(OH)2 with chlorine in a gas jar, a white powder is
produced.
Ca(OH)2
+ Cl2 ⟶ Ca(OCl)Cl
+ H2O
Q. Describe the physical
properties of Bleaching powder.
PYHSICAL
PROPERTIES OF BLEACHING POWDER
1. Bleaching powder is a white amorphous
powder.
2. Its smell like chlorine.
3. It is an oxidizing agent.
Q. Describe the uses of Bleaching
powder.
USES
OF BLEACHING POWDER
1. It is used for bleaching wood
pulp, paper pulp, cotton, linen etc.
2. It is used for sterilization
of water.
3. It is used for quick
preparation of chlorine gas.
4. It is used for disinfecting
drains and sewers.
5. Bleaching powder is used to
prepare hypochlorous acid.
Q. What is Silver Nitrate test?
What is this test used for?
SILVER
NITRATE TEST
Silver nitrate test is come
out for the detection of halide ions in a compound. All the common metallic
halide e.g. NaCl, KBr, MgI2 etc. are soluble in water except halides
of silver and lead.
In silver nitrate test, the
aqueous solution of the common metallic halides is treated with the solution of
silver nitrate.
As a missing of this,
precipitates of silver halides of different colors form which gives information
of particular halide ion.
|
Procedure |
Observations |
Inference / Indication |
|
Given solution + AgNO3 |
White ppt of AgCl turns
purple grey in sunlight |
Cl- is present |
|
Ppt of AgBr turns green
yellow in sunlight |
Br- is present |
|
|
Yellow ppt of AgI has no
effect of sunlight |
I Is present |
Reaction
NaCl + AgNO3 ® AgCl + NaNO3 (while ppt)
NaBr + AgNO3 ® AgBr + NaNO3 (light yellow
NaI
+AgNO3 ® AgI
+ NaNO3 (bright yellow ppt)
Choose the correct option for each of the
following statement.
i.
In the process of electrolysis,
a. Oxidation takes place at
cathode
b. Reduction takes place at
anode
c. Cations are discharged at
cathode
d. Anions are discharged at
anode
ii.
The most abundant and useful halogen is:
a.
F
b.
Cl
c.
Br
d.
I
iii.
It is the only liquid in periodic table:
a.
F
b.
Cl
c.
Br
d.
I
iv.
Chlorine gas prepared in the laboratory is
collected in the gas jar by?
a.
Upward displacement
of water
b.
Downward displacement
of air
c.
Upward displacement
of air
d.
Downward displacement
of water
v.
Chlorine is used in:
a.
Preparation of
bleaching powder
b.
Identification of Br and
I
c.
Dyes, drugs,
explosives etc.
d.
All of the above
vi.
Which of the following will release chlorine
from HCl?
a.
Na
b.
MnO2
c.
KOH
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