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Table 11. Several chareacteristics of the elements in the halogen gruop

Table 11. Several chareacteristics of the elements in the halogen gruop

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Molecule mass

The state of elements in



19



35.5



80



127



gas



gas



liquid



solid



Pale



Greenish-



Reddish-



Purplish-



yellow

-219.6

-188.1

3.98



yellow

-101.0

-34.1

3.16



brown

-7.3

59.2

2.96



black

113.6

185.5

2.66



20oC

Color at room temperature

o



Melting point (m.p, C)

Boiling point (b.p, oC)

Electronegativity



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

gradually.

- 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

compounds.

- 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.



71



EXERCISES

1. Which of the following metals reacts with dilute HCl solution and Cl2 gas to from the

same chloride metal salt?

A. Fe



B. Zn



C. Cu



D. Ag



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.



72



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.

� 71



d= �2.5�



�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,

carbon tetrachloride,...

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:

73



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:

0



0



+1



-1



2 Na  Cl 2 � 2NaCl



Figure 5.1. Copper burns in chlorine

gas



Figure 5.2. Iron burns in chlorine



Red hot copper wire burns



gas



in chlorine gas



Red hot iron wire burns in chlorine



to form copper(II) chloride



gas

to form a brown gas,which are



-1



particles of iron(III) chloride.

+3 -1



0



0



+2



Cu  Cl 2 � CuCl2



0



0



2Fe  3Cl 2 � 2FeCl3



2. Reactions with hydrogen

74



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

1:1.

+1

0 -1



0



H2  Cl2 � 2HCl

Hence, in reactions with metals and hydrogen, chlorine exhibits strongly oxidative

property.

3. Reactions with water

When dissolved in water,



part of chlorine gas reacts with water to form hydrochloric



acid and hypochlorous acid.



-1



+1



0



Cl2 + H2O � HCl +HClO

In the reaction above,chlorine is both a reducing agent and an oxidizing agent

+1



-1



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

bleaching property.

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.

75



IV. APPLICATIONS

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

pulp.

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...

V. SYNTHESIS

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)...

heat

MnO2 + 4HCl ��



� MnCl2  Cl2  2H2O



2KMnO4  16HCl � 2MnCl2  2KCl  5Cl2 �8H2O

Concentrated

HCl solution



NaCl

solution to

trap HCl gas



Concentrated

H2SO4 to

absorb

moist



Cotton soaked with

NaOH solution

Dry Cl2



Figure 5.3.Synthesizing and obtaining chlorine gas in the laboratory



76



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 �

with diaphragm



negative electrode (carthode)



positive electrode (anode)



Viet Tri Chemical Company (Viet Tri City, Phu Tho Province) uses this method.



EXERCISES

1. In the laboratory, which of the following compounds is usually oxidized to synthesize

chlorine gas?

A. NaCl

B. HCl

C. KClO3

D. KMnO4

77



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

phenomenon? Explain.

4. State the practical applications of chlorine.

5. Balance the chemical equations of the following oxidation-reduction reactions with the ion

electron method:



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

reactions?

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?



LESSON 23:

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

Atomic structure



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 ).

Properties

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:

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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

HCl.

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

Physical properties

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



hydrogen chloride



liberates and combines with moist in the air to form tiny solution particles like fog.

Chemical propertices



79



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:

Fe



+



2HCl



CuO +



2HCl



FeCl2 + H2

CuCl2 + H2O



Fe(OH)3 + 3HCl FeCl3 +

CaCO3



+ 2HCl



3H2O



CaCl2



+



CO2



+



H2O



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.

MnO2



+



4HCl



MnCl2



+



Cl2



+ 2H2O



3. Synthesis

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

Figure

5.6:



Synthesizing hydrochloric acid in the laboratory

b, Manufacture of hydrochloric acid in industry

80



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



2HCl



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,

PbCl2

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

81



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Table 11. Several chareacteristics of the elements in the halogen gruop

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