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Chlorine and its Compounds

Click on the grid shown to indicate the position of Chlorine in the periodic table.

By the end of the lesson the learner should be able to:-
a) Describe and explain laboratory preparation of chlorine.
b) State and explain properties and uses of chlorine.
c) Explain environmental pollution caused by chlorine.
 

In form 2 we learnt that Chlorine is an element in the periodic table with atomic number 17 and mass number 35.

Atomic and mass number of Chlorine

Chlorine gas

Chlorine gas is diatomic and is prepared in laboratory by action of concentrated hydrochloric acid with potassium manganate(VII)NB: chlorine is poisonous, should be prepared in fume cupboard or well ventilated room.Click to play the following video clip and observe the preparation of Chlorine gas.


 

The observation made from the experiment, indicate that chlorine is a yellow-green gas. It has unpleasant, pungent and irritating smell. Chlorine is fairly soluble in water. It is also denser than air and that is why it is collected by downward delivery or upward displacement of air. The gas is passed through water to dissolve hydrogen chloride gas. This is highly soluble in water. To collect dry sample of chlorine gas, it is passed through concentrated sulphuric acid.

16HCl(aq) + 2KMnO4(s) w 2KCl(aq) + 2MnCl2(aq) + 8H2O(l) + 5Cl2(g)
Chlorine gas reacts with metals to form metal chloride.
 

Chlorine gas reacts with metals to form metal chloride. Click to play the following video and observe what happens when a burning Magnesium ribbon is inserted into a gas jar containing chlorine gas.

 

Magnesium ribbon is cleaned using sand paper to remove oxide coating on it, formed after a long time exposure in air. On burning magnesium it produces white brightly flame. On placing it on gas jar containing chlorine, it continues burning brightly forming a white solid.
Conclusion:
Magnesium reacts with chlorine to produce white solid of magnesium chloride. The equation for the reaction is written as follows
Mg(s) + Cl 2(g) w Mg Cl 2(s)
White solid

Iron reacts with chlorine as shown in the following animations. Click on the tab with the gas to observe what happens.

Iron reacts with dry chlorine gas to form iron (III) chloride crystals. These crystals sublime on heating therefore formed at receiver flask. Iron (III) chloride crystals are deliquescent, meaning they absorb water from the atmosphere to form solution. Therefore a drying agent for example anhydrous calcium chloride or anhydrous calcium oxide is placed in receiver flask.
The equation for the reaction is
2Fe(s) + 3Cl 2(g) w 2FeCl 3(s)

Chlorine reacts with hydrogen sulphide. The following animation shows the reaction.

Chlorine oxidizes hydrogen suphide gas to sulphur at room temperature. Chlorine is on the other hand reduced by hydrogen sulphide to hydrogen chloride. Chlorine is oxidizing agent and hydrogen sulphide is reducing agent.

Cl2(g) + H2S(g) w 2HCl(g) + S (s)

To understand the bleaching action of Chlorine gas moist blue and red litmus papers are placed in a gas jar containing Chlorine gas.Coloured flower petals are also placed in another gas jar of Chlorine gas.Click to play the following video clip and observe what happens.

Chlorine gas bleached moist coloured substances. Blue litmus paper changes red because chlorine gas is acidic and therefore forms acidic solution when dissolved in water. However, red litmus changes to white.

Chlorine gas reacts with water to form hypochlorous acid and hydrochloric acid.

Cl2(g) + H2O(g) w HOCl (aq) + HCl (aq)
Hypochlorous acid contains atomic or nascent oxygen
H[O]Cl
The atomic oxygen is unstable and therefore easily removed from hypochlorous acid in presence of sunlight to form hydrochloric acid and oxygen gas.

2H[O]Cl(aq) w2 HCl(aq) + O2(g)
In the presence of coloured sustance,the atomic oxygen oxidises the dye therefore bleaching the substances.
 

The following video clip shows displacement reactions that take place when Chlorine gas is bubbled through different Halogen Halides. Click to play the video and observe what happens carefully.

Chlorine gas is bubbled into colourless potassium bromide solution.The solution turns to brown due to formation of bromide solution. Chlorine gas on the other hand when bubbled into potassium iodide solution turns dark brown solution and finally a black solid of iodine is deposited.
Conclusion
Chlorine is more reactive than bromine and therefore displaces it from its solution to form bromine water.

2KBr(aq) + Cl2(g) w 2KCl (aq) + Br2(aq)
Chlorine is more reactive than iodine and therefore displaces it from to form iodine solid.

2KI(aq) + Cl2(g) w 2KCl (aq) + I 2(s)
Brown bromine gas also displaces iodine to form dark brown solution and finally black solid of iodine.

2KI(aq) + Br 2(g) w 2KBr (aq) + I 2(s)
The order of halogen therefore can be written as
 

The following video clip shows the procedure of testing for the presence of a Chloride. Click to play the video clip to observe what happens.

Sodium chloride solution reacts with silver nitrate solution to form a white precipitate of silver chloride which is insoluble in nitric acid.
The equation for the reaction is as follows:

NaCl (aq) + AgNO3 (aq) w AgCl (s) + NaNO3 (aq)

Sodium carbonate solution on the other hand reacts with silver nitrate to form silver carbonate as shown in the equation.

NaCO3 (aq) + AgNo3 (aq) w Ag CO3 + NaNO3 (aq)
However, silver carbonate reacts with nitric acid to form silver nitrate, therefore dissolving the precipitate.

If silver nitrate is added to unknown solution and forms white precipitate which dissolves in acid, then the unknown sample contains carbonate ions. However, if white precipitate is insoluble in the acid, the sample under test contains chloride ions

The following are some of the uses of Chlorine.

Pollution effect of chlorine in the environment

Organic chlorine compounds are organic compounds in which chlorine is strongly bound to carbon. They are highly stable, cannot be decomposed by micro organism and therefore remain in the environment thus are non-biodegradable. They eventually accumulate in body fat of fish, animals and ultimately in human through food.

Insecticides, fungicides valenticides and herbicides such as DDT are highly toxic to fish and birds and may cause cancer to humans i.e. it is carcinogenic.

Dioxins are compounds containing carbons, chlorine, hydrogen and hydrogen and oxygen. They are formed when plastics such as pvcs are burned or incinerated. They are high in toxic and cause birth defects, liver damage and cancer.

Chlorofloro carbons (CFCs)such as CCL2F2 are used as refrigerant gases in refrigerators and air conditioners. The CFCs breakdown in upper atmosphere and releases chlorine which destroys ozone layer. The uv traclichon as alcsuses cause such cancers and global warming.

Polychlorinated biphenyls (PCBs) are stable compounds that resist heat, acids, base and oxygen. They are used in transformers in electricity substances. They cause liver ailments, skin lesions and damage to the nervous system.

By the end of this topic, the learner should be able to

:
a) Describe the preparation of hydrogen chloride gas
b) State and explain the properties and uses of hydrogen chloride gas
c) Explain the effect of solvent on the properties of hydrogen chloride
 

In this lesson we will discuss Hydrogen Chloride gas, preparation, properties and uses.

The reagents used Sodium chloride solid and Concentrated sulphuric acid
Study the experiment shown that is used to prepare hydrogen chloride gas.

Conc. Sulphuric acid reacts with sodium chloride according to the equation

NaCl(s) + H2SO4 (l) w NaHSO4(aq) + HCL (g)

Hydrogen chloride gas is a colourless gas that is denser than air. Hence it is collected by downward delivery
The gas is very soluble in water and gives the fountain experiment.

The following animation shows the reaction between Hydrogen Chloride gas and Ammonia solution. Observe what happens.

Hydrogen chloride gas reacts with ammonia gas to form dense white fumes of ammonium chloride.

This reaction is used as a test for the gas.

What happens when hydrogen chloride gas is bubbled into silver nitrate solution? Observe the following animation then answer the question that follows:

Hydrogen chloride gas reacts with silver nitrate solution to form insoluble silver chloride salt.

HCl (g) + AgNO3(aq) w AgCl (s) + HNO3(aq)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   

 

By the end of this topic, the learner should be able to

:
a) Explain the effect of a solvent on the properties of hydrogen chloride gas
b) Describe the industrial manufacture of hydrochloric acid
 

In this lesson we will discuss the effects of solvents on the properties of Hydrogen chloride solution. We will also discuss the large scale manufacture of Hydrochloric acid.

The Animation below shows different tests carried out when Hydrogen Chloride gas is dissolved in water and Hydrogen Chloride gas is dissolved in methyl benzene.

Into the first test tube labeled A and B place blue and red litmus paper and observe what happens.
Into the second test tubes labeled A and B put a small piece of magnesium ribbon. Observe what happens.
Into the third test tubes labeled A and B add a small amount of sodium carbonate solid and observe what happens.
Into the 4th test tube labeled A and B add 2-3 drops of phenolphthalein indicator followed by addition of drops NAOH with shaking until there is a permanent colour change.Observe what happens.
Into the 5th test tube A and B add a small amount of copper (II) oxide solid. Carefully observe what happens.

From the video clip the following results were obtained. Click on each of the tests to observe the results obtained.

Hydrogen Chloride gas dissolved in water and in methylbenzene
When hydrogen chloride gas is dissolved in water it dissociates:
The presence of H+ ions makes the solution acidic
The solution shows the acid properties for example
Reaction with Magnesium ribbon
React with metals to form salt and liberate hydrogen gas
Reaction with sodium carbonate
The solution reacts with carbonates and hydrogen carbonates to give a salt, water and carbon (IV) oxide gas
Reaction with alkalis
The solution neutralizes alkalis to form salt and water
Reaction with a base
The solution also react with an insoluble base to form salt and water only.
The reaction react with strong oxidizing agents like potassium manganate (VII) without heating to give chlorine gas
However when hydrogen chloride gas is dissolved in organic solvents like methylbenzene, it does not ionize. The gas retains the properties of covalent compounds. This explains why there is no reaction between hydrogen chloride gas dissolved in methylbenzene and metal carbonates base and litmus paper.
 

The following animation shows the industrial mannufacture of Hydrochloric acid.

The raw materials are hydrogen gas and chlorine gas all obtained by electrolysis of aqueous sodium chloride (brine)
When hydrogen is burnt in chlorine gas, hydrogen chloride is formed.

H2(g) + Cl2(g) w 2HCl(g)
The reaction can be explosive and therefore it is controlled by allowing a small quantity of hydrogen through a jet to burn in excess chlorine.
The hydrogen chloride formed is then dissolved in water over glass beads to form hydrochloric acid.

The glass beads increases the surface area over which absorption takes place.
The acid is stored or transported in steel tanks which are lined inside with rubber. If the acid comes into contact with a part of the steel or rust, Iron II Chloride is formed which is later oxidized by air to Iron (III) oxide.

The following are some of the uses of Hydrocloric acid.

To standardize PH of beers and wines
In prickling of metals
In the manufacture of dyes, drugs

In the manufacture of photographic materials
In school and research laboratories

 




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