Production of chlorine

Aim:

My aim is to compare the production of chlorine in the laboratory and in the industry.

Introduction:

Chlorine, Cl, is a poisonous greenish-yellow gaseous non-metallic element, found in Group VIIb (i.e. the Halogen Group of elements) of the periodic table.

It has two Isotopes

Atomic Number : 17
Atomic Mass : 35.453
Melting Point : -101 degC
Boiling Point : -35 degC
Density : 0.003

Chlorine is easily liquefied under pressure.

History of chlorine:

Chlorine was discovered by Karl Wilhelm Scheele, a Swedish chemist, in 1774. Scheele thought that chlorine was an oxide of murium, or hydrochloric acid. Scheele heated manganese dioxide and hydrochloric acid and discovered this greenish, yellow gas. He did not, however, establish chlorine as an element. In 1810, chlorine was named and classified as an element by Humphrey Davy. It was named after the Greek word chloros, which means pale green.

Chlorine has also been used during World War I. It was first introduced as a weapon on April 22, 1915 at Ypres by the Germans. The results of this weapon were disastrous because gas makes had not yet been invented. But, some compounds of chlorine are more dangerous and have replaced chlorine gas on the battle field. They are phosgene, chloropicrin, Lewsite, and mustard gas.

Production of Liquid Chlorine in the industry:

Chlorine is an industrial chemical that is identified by the symbol Cl2.

Chlorine is almost entirely produced by electrolysis in the industry. The electrolysis process includes fused chlorides or solutions of alkali metal chlorides. The pure chlorine is produced at a graphite anode while hydrogen, along with sodium or potassium hydroxide is produced at the cathode. Pure chlorine is never found in nature but is often produced for industrial uses.

Production of Chlorine gas in the industry:

Chlorine Chemistry starts with ordinary salt - sodium chloride - a stable, natural substance that flows constantly through the ecosystem and our bodies. The chemical industry creates chlorine gas (Cl2) by passing huge quantities of electricity through salt water, splitting the salt molecule and fundamentally changing the character of the chlorine in it. Chlorine gas is an extremely reactive and poisonous substance that rarely occurs in nature. At normal temperatures and pressures, chlorine gas is heavy, yellow-green gas with a sharp, irritating odour.

Industrial method of chlorine gas:

On industrial scale CL2 is obtained by the electrolysis of aqueous solution of NaCl called Brine. 2NaCl +2H2O ➔ Cl2+H2 + 2NaOH

Ionization of NaCl

NaCl Na+ + Cl-

Electrolysis means using an electric current to separate a mixture of ions.

Reaction at Anode:

Cl- ions are collected at anode and form chlorine gas

2Cl-➔ Cl2+ 2e-

Reaction at Cathode:

Na+ ions are collected at cathode where they are mixed with water to produce sodium hydroxide and liberate hydrogen gas.

2Na+ + 2H2O + 2e-➔ 2NaOH + H2

Overall reaction:

2Na+ + 2H2O + 2e-➔ 2NaOH + H2
2Cl-➔ Cl2+ 2e-

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2Na+ 2Cl- + 2H2O➔ 2NaOH + Cl2 +H2

Unlike ionic chlorine, chlorine ...

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2Cl-➔ Cl2+ 2e-

Reaction at Cathode:

Na+ ions are collected at cathode where they are mixed with water to produce sodium hydroxide and liberate hydrogen gas.

2Na+ + 2H2O + 2e-➔ 2NaOH + H2

Overall reaction:

2Na+ + 2H2O + 2e-➔ 2NaOH + H2
2Cl-➔ Cl2+ 2e-

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2Na+ 2Cl- + 2H2O➔ 2NaOH + Cl2 +H2

Unlike ionic chlorine, chlorine (i.e. salt) gas bonds quickly with organic matter to form a new class of chemicals called ‘organ chlorines’, most chlorine is combined with petrochemicals to produce organ chlorine products including plastics (especially PVC or Vinyl), pesticides, solvents and other chemicals. Many more organ chlorines are produced by accident. Because chlorine is so reactive, it combines quickly with organic matter to form a variety of very toxic by-products and wastes. Hundreds of these accidental organ chlorines are released when chlorine is used to bleach pulp, disinfect water, manufacture other organ chlorines, and whenever chlorine-containing chemicals are burned. These by-products - including the infamous dioxins and furans - are sometimes even more dangerous that the intentionally produced chemicals. Chlorine gas itself has been found to be contaminated with dioxin-like compounds and high concentrations of dioxin have also been found in sludges from spent graphite electrodes used in the production of chlorine.

Storage of Chlorine produced in the industry:

Chlorine is stored and shipped as a liquid under pressure in steel containers. If a containers leaks, liquid chlorine could be present for a very short time. Liquid chlorine is an amber-colored, oily fluid; under normal conditions, it evaporates (changes to a gas) very rapidly. Chlorine can be combined with other chemicals to produce products that are stable and exist as solids or liquids at normal temperatures and pressures.

Forms of which Chlorine in the industry can be handled:

The three forms in which small system usually handle chlorine are chlorine liquid and gas (in steel cylinders); calcium hypochlorite (a solid or powder); and sodium hypochlorite (a liquid).

Chlorine gas:

Chlorine gas is approximately 2.5 times heavier than air. Because it is heavier than air it sinks in most cases and accumulates in low spots. It is yellow –green in colour ands has a strong, penetrating odour. Liquid chlorine will change to a gas very rapidly under normal atmospheric condictions. One part of liquid chlorine will form 459 parts of gas when it evaporates. The chlorine gas used to disinfect water is shipped and store as a liquid in silver-colored, pressurized cylinders (usually referred to as gas cylinders).

There sizes of gas cylinders are commonly used to store chlorine gas they are 100-lb (limited in use) and 150-lb cylinders and to containers. Most large water treatment plants use the 150-lb cylinders. Most large water treatment plants use ton containers. All types of chlorine containers bear a green or white label that reads "liquid chlorine __ Non-flammable Compressed Gas". A 150-lb cylinder contains 150-lb (68 Kg) of chlorine. At normal ambient temperatures, about 80 percent of the volume of the cylinder is liquid chlorine and the other 20 percent is chlorine gas. Because the gas is lighter than the liquid, it is always at the top of the container.

Laboratory preparation of chlorine:

A gas jar of chlorine gas is prepared by reacting concentrated hydrochloric acid on potassium permanganate crystals. Chlorine is heavier than air, so it can be allowed to collect at the bottom of a gas jar, forcing the air out of the top.

Hydrochloric acid + potassium permanganate ➔ chlorine + water + manganese chloride + potassium chloride

16HCl(aq) + 2KMnO4(s) ➔ 5Cl2(g) + 8H2O(l) + 2MnCl2(aq) + 2KCl(aq)

Other chemicals used in the laboratory to produce chlorine:

First method: -

In laboratory Cl2 gas can also prepared by heating a mixture of NaCl, MnO2 with conc. H2SO4.

4NaCl +4H2SO4 +MnO2➔ 4NaHSO4 +MnCl2+2H2O +Cl2

Second Method: -

Chlorine may also be obtained by heating manganese dioxide with concentrated hydrochloric acid.

MnO2 + 4HCl ➔ MnCl2+2H2O +Cl2

Uses

Chlorine is used for: -

For the manufacture of bleaching powder and liquid bleaches,
To bleach fabrics (e.g. linen and cotton), wood pulp and paper,
In the manufacture of a wide range of chloro-organic solvents, including Methylene Chloride, CH2Cl2, Chloroform, CHCl3, Carbon Tetrachloride, CCl4,
In the manufacture of a number of important inorganic chemicals, including Sulphur Chloride, S2Cl2, Thionyl Chloride, SOCl2, Phosgene (i.e. Carbonyl Chloride), COCl2, and inorganic Chlorates, (e.g. Sodium Chlorate, NaClO3),
For the direct manufacture of Hydrochloric Acid by the direct combination of its elements,

H2 + Cl2 ==> 2 HCl

For the extraction of Gold from its ores,
In the manufacture Sodium Hypochlorite (i.e. domestic bleach), disinfectants, insecticides, plastics and Hydrochloric Acid,
As a disinfectant used to kill bacteria in the preparation of drinking water.
The Germens at the world war used chlorine gas as a weapon in 1915.
Chlorine is also important in the manufacture of paints, aerosol propellants and plastics.

Comparing the production of chlorine in the industry and in the laboratory:

With the information I have about chlorine. I can say that the production of chlorine in the laboratory is much less in amount compared to the amount produced in the industry. The reason for this is because the industry supplies the chlorine used all over the world and in the other industries which use it to make other products as bleaches but in the laboratory the chlorine produced is just for tests and experiments and the lab technicians don’t need much of it. Also there are special equipments present in the industry for producing high amounts of chlorine and many people are employed to do the job. In the laboratory, there are only simple equipments like Andrew’s gas generator for producing chlorine. In the industry chlorine is produced by electrolysis and they can use different chemicals to form chlorine. In the industry there is needed a more qualified personnel because there are more risks which can occur while as in the laboratory the risks are less. Also in the industry there is much air pollution where the employees need to be more careful.

I am going to produce chlorine gas and liquid in the laboratory.

Hypothesis:

I predict that if I mix the two chemicals: Hydrochloric acid (HCl) and Sodium Chlorate (NaClO) I will get a green yellowish form which will smell like bleach.

Equipments:

Andrew gas generator--- Andrew gas generator is equipment which has two flasks, top one and bottom one and a tap at the middle. The main use of it is to prevent gas from spreading out while doing experiments in the laboratory. These gases may smell and can be harmful to human’s health if inhaled so the gas generator is very important.

Fume cupboard— a fume cupboard is used to prevent the gas from spreading out while doing exeperiments in the laboratory. It is connected to ventilation where all the gases escape to the air.

Conical flask -- the conical flask has the same properties as a beaker but it has a different shape. Because its neck is narrow a delivery tube can be fitted into it.

Rubber stopper (cock)—a rubber stopper is used to stop the gas from coming out. It has a hole where a glass tube can be inserted.

Glass tube--- Glass tube is also called delivery tube which is used as a path for gas/liquid to pass through to the other beaker or conical flask.

Hydrochloric acid (HCl) ----- Hydrochloric Acid is a clear, colourless, toxic and corrosive liquid. It chiefly finds use in metal cleaning, descaling, bleaching, hydrolyzing agent and industrial solvent for inorganic compounds.

Sodium Chlorate (NaClo) --- Sodium chlorate is a powerful oxidizing agent. It is used to manufacture explosives and matches because of its ability to produce oxygen. Chlorate is a powerful ingredient of bleaching powder used in paper and pulp processing and calico printing. It is used also a weed killer and defoliant. Sodium chlorate can found in granules and in liquid form.

Safety:

I will not inhale chlorine gas because it can cause lung congestion, pulmonary edema, pneumonia, pleurisy, and bronchitis.
I will work in a fume cupboard for the gas to escape. And also a well ventilated room.
I will wear protective goggles to protect my eyes.
Chlorine is a toxic substance and misuse could mean death so I will use it appropriately.
I will keep away from heat.
I will wear groves because chlorine is irritant and may cause serious permanent skin damage.

Method: for chlorine liquid.

A simple method of producing liquid chlorine in the laboratory would be to take a conical flask and pour some little sodium chlorate (NaClo) (which is white in colour) and add a few drops of hydrochloric acid (HCl). Then swirl the conical flask. Both the liquids are crystal white in colour but when they mix and react, they give out a yellow green chlorine colour.

Method: for chlorine gas.

We used Andrew, gas generator. Andrew, gas generator has two flasks top and bottom. The top flask had cock attached to it in which we pour HCl at a random amount. The bottom flask had granules of powdered sodium chlorate (NaClo). The reason for using powdered sodium chlorate is because we needed the gas. When we were ready to release the stopper (cock), we attached the Andrew’s gas generator using a delivery tube so that the chlorine gas could be collected. Once we are ready we opened the tap and get the HCl to sodium chlorite which produces chlorine gas.

Diagram:

Observation:

Fumes of green colour were seen collected in the flask and we tested for hydrogen gas with a pop test.

Conclusion:

My experiment was successful and I tested the gas I produced with a burning sprint. There was a pop sound which indicates hydrogen was present. My prediction was correct because when I mixed the two chemicals sodium chlorate and hydrochloric acid, they both reacted and gave me a result of a green yellowish form which smelled like bleach.

Evaluation:

Although this was a successful experiment, there were some factors of the experiment, which could have been improved to make it even more successful. One of these factors could have been the amount of chemical I used. I had a random amount of hydrochloric acid and sodium chlorate. If I were to do this experiment again I would try and measure the chemicals I use to make my test fair. I would also monitor the amount of chlorine produced by a certain amount of each chemical. E.g. when I put 20 ml of hydrochloric acid and 20 ml of sodium chlorate, am I getting 40 ml of chlorine?