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Table 11. Several chareacteristics of the elements in the halogen gruop
The state of elements in
Color at room temperature
Melting point (m.p, C)
Boiling point (b.p, oC)
1. Changes in the physical prooerties of the halogen elements
From fluorine to iodine it can be seen
- Mater state: From gaseous state, it changes into liquid anh then solid.
Color: The color of the halogen become darker.
- Melting points and boiling points: Increase gradually.
2. Changes in Electronegativity
- The electronegativities of halogen are rather high.
- Going down from fluorine to iodine, the electronegativity is expected to decrease
- Fluorine has the highest electronegativity hence in all its compounds, fluorine only has
oxidation number of -1. Besides of oxidation nuber of -1, other halogen elements also
have the oxidation number of +1, +3, +5, +7.
3. Changes in chemical properties of the halogen elements
- Because of the similarity in the outermost electron shell (ns2np5), the halogen have the
similarities in chemical properties as well as the composition and properties of the their
- The halogen are representative non-metals. From fluorine to iodine,the oxidative
properties derease gradually.
- Halogen can oxidize most of the metalsto from halide salts and hydrogen gas to from
colorless gaseous halide compounds. These gaseous compounds dissolve in water to
from hydrohalic acid solutions.
1. Which of the following metals reacts with dilute HCl solution and Cl2 gas to from the
same chloride metal salt?
2. Which of the following features is not the feature of the halogen (F, Cl, Br, I)?
A. The atom can gain one more eletron.
B. Has the ability to from polar covalent bond compound with hydrogen.
C. Has the oxidation number of -1 in every compound.
D. The outermost electron shell has 7 elctrons.
3. Which of the following features is the general feature of halogens (F2, Cl2, Br2, I2)?
A. Is gaseous compound at normal conditions.
B. Has strong oxidative proprety.
C. Has both oxidative prroperty and reductive property.
D. Reacts strongly with water.
4. Compare the halogens in the following aspects:
a) Atomic structure and molecular structure.
b) Physical properties.
c) Chemical properties.
5. State the periodic variations in melting point, boling point, colour and electronenagetivity
of the halogen.
6. State the basic chemical properties of the halogens and explain the change direction in
these chemical propreties.
7. Explain why the halogens do not occur free in nature.
8. An amount of a halogen reacts completely with magnesium to from 19g of magnesium
halide. The same amount of this halogen reacts completely with alumininum to form 17,8g
of alumininum halide. Determine the name of the halogen and the amount of the halogen
has seen used.
Lesson 22: CHLORINE
Chlorine is the most repesentative and important halogen.
What are its physical propreries and chemical properties?
What applications does chlorine have and how is it synthesized?
I. PHYSICAL PROPERTIES
In normal conditions,chlorine is a greenish-yellow, pungent, very toxic gas.It can destroy
the mucosa of respiratory tract.
�and can dissolve in water. At
Chlorine gas is 2.5 times heavier than air � 29
20oC, one volume of water can dissolves 2.5 volumes of chlorine gas. The solution of
chlorine gas in water is called chlorine water and its color is light yellow.
Chlorine gas can dissolve strongly in organic solvents such as benzene, ethanol, hexane,
II. CHEMISCAL PROPERTIES
Chlorine atom with a high electronegativity (3.16) stands only after fluorine atom (3.98)
and oxygen atom (3.44). Hence, in the compounds contating these elements, it exhibits
positive oxidation number (+1, +3, +5, +7) and in other cases, it shows negative
oxidation number (-1).
When participainting in chemical reactions, chlorine atom can easily gain one more
electron to from a chloride ion Cl-.
Hence, the basic chemical property of chlorine is that it has strong oxidative property.
This property is represented in the following reactions:
1. Reactions with metals
Chlorine gas can directly oxidize most metals to form chlorine salts. The reactions
occuring at normal or not so high temperatures has high speed, and releases much heat.
Molten sodium burns in chlorine gas with a bright flame to form sodium chloride:
2 Na Cl 2 � 2NaCl
Figure 5.1. Copper burns in chlorine
Figure 5.2. Iron burns in chlorine
Red hot copper wire burns
in chlorine gas
Red hot iron wire burns in chlorine
to form copper(II) chloride
to form a brown gas,which are
particles of iron(III) chloride.
Cu Cl 2 � CuCl2
2Fe 3Cl 2 � 2FeCl3
2. Reactions with hydrogen
At ambient temperature and in the dark,chlorine gas almost hardly react with hydrogen
gas. When the mixture is exposed by the sun or light of burning magnesium, the reaction
occurs rapidly and may explode. The mixture can explode the most strongly when the
molar proportion between hydrogen and chlorine
H2 Cl2 � 2HCl
Hence, in reactions with metals and hydrogen, chlorine exhibits strongly oxidative
3. Reactions with water
When dissolved in water,
part of chlorine gas reacts with water to form hydrochloric
acid and hypochlorous acid.
Cl2 + H2O � HCl +HClO
In the reaction above,chlorine is both a reducing agent and an oxidizing agent
because a Cl atom is oxidized into Cl and a Cl atom is reduced to Cl. The reaction above
is a reversible reaction because HClO is very strong oxidizing agent which can oxidize
HCl into Cl2 and H2O. Since HClO is a strong oxidizing agent, chlorine water has a high
III. NATURAL OCCURRENCE
In natural, chlorine has two stable isotopes: 35Cl (75.77%) and 37Cl (24,23%), average
molecular weight is 35.5.
Due to its high reactivity, chlorine element only occurs in nature in the form of
compounds, mostly sodium chloride salt in sea water and rock salt. One litre of seawater
contains approximately 30g of sodium chloride salt. Another compound of chlorine
which is also abundant in nature is carnallite mineral KCl.MgCl2.6H2O. Hydrochloric
acid also occurs in stomach gastric juice of humans and animals. Chlorine occupies about
2% of the weight of seawater.
a) Chlorine is used to disinfect public water supplies. A small amount of chlorine is
dissolved into water to kill bacteria that cause diseases. Water for swimming pools can be
treated wiht a larger amount of chlorine gas. It is aslo used to bleach fiber, textiles, wood
b) A large amount of chlorine is used to produce organic chemicals. The products with
chlorine have enormous applications. The solvents such as carbon tetrachloride,
dichloethane are used widely to extract fat anh remove grease from metals. Some organic
compounds with chlorine are used as pesticides. From organic products containing
clorine, many types of plastics such as PVC-poly(vinyl chloride), synthetic rubbers,
synthetic fibers...are manufactured.
c) Chlorine is used to produce bleach,germicides such as Javen water,chloride of lime and
produce inorganic chemicals such as hydroclodric acid,potassium chlorate...
1. Synthesizing chlorine in the laboratory
In the factory,chlorine gas is synthesized by the reaction of concentrated hydrochloric
acid with a strong oxidzing agent such as solid manganese dioxide (MnO2) or solid
potassium permanganate (KMnO4)...
MnO2 + 4HCl ��
� MnCl2 Cl2 2H2O
2KMnO4 16HCl � 2MnCl2 2KCl 5Cl2 �8H2O
trap HCl gas
Cotton soaked with
Figure 5.3.Synthesizing and obtaining chlorine gas in the laboratory
It is necessary to heat up MnO2, but KMO4, may or may not be heated up. Obtained
chlorine gas usually contains impurities like hydrogen chloride gas and steam. To remove
the impurities ,chlorine gas is introduced sequentially through gas wash wash bottles
containing NaCl solution (to trap HCl gas) and concentrated H2SO4 (moist absorption).
2. Manufacture of chlorine in industry
In industry, the electrolysis of saturated sodium chloride solution in water (figure 5.4) is
carried out to produce caustic soda (NaOH) as well as to abtain clorine gas and hydrogen gas
(chlorine as the by-product for froducting caustic soda technology). The electrolysis barrel
has a diapharagm separating 2 electrodes to prevent chlorine gas.
Figure 5.4.Producing NaOH,Cl2 gas,H2 gas in industry
The equation of the electrolysis can be written as follows:
electrolyse of sodium
2NaCl + 2H2O �������
2NaOH H2 � Cl2 �
negative electrode (carthode)
positive electrode (anode)
Viet Tri Chemical Company (Viet Tri City, Phu Tho Province) uses this method.
1. In the laboratory, which of the following compounds is usually oxidized to synthesize
2. State the basic chemical propertiesn of a chlorine element. Explain why a chlorine exhibits
them. Give illustrative examples.
3. When chlorine gas is introduced into water,which will occur, physical or chemical
4. State the practical applications of chlorine.
5. Balance the chemical equations of the following oxidation-reduction reactions with the ion
a) KMnO4 HCl � KCl MnCl2 Cl2 H2O
b) HNO3 HCl � NO Cl2 H2O
c) HClO3 HCl � Cl2 H2O
d) PbO2 HCl � PbCl2 Cl2 H2O
6. Why is the electrolysis of concentrated sodium chloride (brine) used in to produce
chlorine gas without using the interaction between substances in oxidadation-reduction
7. How many grams of KMnO4 and millilitters of 1M hydrochloric acid are are needed to
synthesize an efficient amount of chlorine gas which can with iron to from 16.25g of FeCl3?
HYDROGEN CHLORIDE HYDROCHLORIC ACID CHLORIC SALT
Does hydrocholric acid exhibit all general chemical properties of acids?
What are its properties that are different from orther acids?
How is a choride ion identifiend?
I – HYDROGEN CHLORIDE
H – Cl
Hydrogen chloride is a covanlent compound with polar molecule ( with the difference in the
electronegativity between chlorine atom and hydrogen atom 3.16 – 2.20 = 0.96 ).
Hydrogen choride is a colorless, pungent, heavier - than – ari gas
( = 1,26 )
To study the solubility of HCl gas in water, the following experiment is carried out:
Cover a jar filled with HCl gas with a rubber cap. Put a straight glass tube tapered at the top
through the rubber cap. Dip the glass tube into a pot of water containing a few drops of
purple litmus solution ( figure 5.5 ).
A moment later, water from pot erupts into the jar through glass tube, forming red trickles.
Why dose water erupt into the jar?
That is because hydrogen chloride gas dissolves strongly in water, creating a drastic decrease
of pressure in the jar, atmospheric pressure pushes the water into the jar to replace dissoveed
The collected solution is acid, so it causes the litmus solution to turn red
Hence, HCl gas dissolves strongly in water. With an accurate experiment, it can be
determined that at 20℃, approximately 500 volumes of HCl gas can be dissolved in one
volume of water.
II – CHLOHYDRIC ACID
Hydrogen chloride dissolves in water to form hydrochloric acid. It is a colorless, pungent
gas. The most concentrated HCl solution ( at 20℃ ) reaches the concentrantion of 37% and
has the density of D = 1.19 g/cm3
Concentrated HCl solution “ fumes” in moist air. That is because
liberates and combines with moist in the air to form tiny solution particles like fog.
Hydrochloric acid is a strong acid with all general chemical properties of acid sush as turning
litmus red, reacting with metals standing above hydrogen in the reactivity series and basic
oxides, bases, and salts. For example:
FeCl2 + H2
CuCl2 + H2O
Fe(OH)3 + 3HCl FeCl3 +
Hydrochloric acid exhibits oxidative proprerty because in HCl molecule and chlotine
element has the lowest oxidation number of -1. When concentrated HCl solution reacst with
strong oxidizing agents such as MnO2 and KMnO4, it is oxidized into Cl2.
a, In the laboratory
Hydrogen chloride can be synthesized by the reaction of NaCl crystal with concentrated and
hot H2SO4 solution ( called the sulfate method), then the hydrogen chloride gas formed is
absorbed in water to obtain hydrochloric acid:
NaCl + H2SO4 NaHSO4 +HCl
At higher temperature Na2SO4 and HCl gases are formed:
2 NaCl + H2SO4 Na2SO4 + 2HCl
Synthesizing hydrochloric acid in the laboratory
b, Manufacture of hydrochloric acid in industry
H2 gas is burned in Cl2 atmosphere ( Cl2 and H2 as the products of the electrolysis process
using a diaphragm of NaCl solution) to form HCl gas ( called the integrated method):
H2 + Cl2
Figure 5.7:The scheme of equipment for industrial manufacture of hydrochloric acid
It is necessary to make the initial combustion for the reaction in the combustion chamber of
the tower T1 ( made from graphite), then the reaction will occur by itself
HCl gas is absorbed by water in the tower T2 and T3 following the upstream principle to
obtain hydrochloric acid
- Nowadays, the technology of producing HCl from NaCl and H2SO4 is also applied in dustry
( called the sulfate method)
- A large amount of HCl is obtained in industry from the chlorination process of organic
compounds ( mainly hydrocarbon)
III – CHLORIDE SALT AND IDENTIFICATION OF CHLORIDE ION
1. Some chloride salts
Salts of hydrochloric acid are called chloride salts. Most chloride salts dissolove a lot in
water, except some insoluble salts such as AgCl and slightly soluble salts such as CuCl2,
Chloride salts have many important applications: KCl is used as potassium fertilizer; ZnCl 2
is impregnated into the wooden sleepers to prevent them from rotting because this substance