Chlorine Properties, Production and Applications
Chlorine
Chlorine is
one of the most commonly used disinfectants for water disinfection. Chlorine
can be applied for the deactivation of most microorganisms and it is relatively
cheap.
When was chlorine discovered?
When was chlorine discovered?
Chlorine gas was presumably discovered in the thirteenth century. Chlorine (Cl2)
was first prepared in pure form by the Swedish chemist Carl Wilhelm Scheele in
1774.
Scheele
heated brown stone (manganese dioxide;
MnO2) with hydrochloric acid (HCl). When these substances are heated
the bonds are broken, causing manganese chloride MnCl2),
water (H2O) and chlorine gas (Cl2) to form.
Reaction
mechanism:
MnO2 + 4HCl -> MnCl2 + Cl2 + 2H2O
MnO2 + 4HCl -> MnCl2 + Cl2 + 2H2O
Scheele
discovered that chlorine gas was water-soluble and that it could be used to
bleach paper, vegetables and flowers. It also reacted with metals and metal
oxides.
In 1810
sir Humphry Davy, an English chemist who tested fundamental reactions of
chlorine gas, discovered that the gas Scheele found must be an element, given
that the gas was inseparable. He named the gas ‘chlorine’ (Cl), after the Greek
word ‘chloros’, which means yellow-greenish and refers to the color of chlorine
gas (White, 1999. Watt, 2002)
Where can chlorine be found?
Chlorine can be found on many different locations all over the world. Chlorine is always found in compounds, because it is a very reactive element. Chlorine can usually be found bond to sodium (Na), or in kitchen salt (sodium chloride; NaCl). Most chlorine can be found dissolved in seas and salty lakes. Large quantities of chlorine can be found in the ground as rock salts or halite.
The properties of chlorine
Chlorine (Cl2) is one of the most reactive elements; it easily binds to other elements. In the periodic chart chlorine can be found among the halogens.
Other halogens are fluorine (F), bromine (Br), iodine (I) and astatine (At). All halogens react with other elements in the same way and can form a large quantity of substances. Halogens often react with metals to form soluble salts.
Chlorine atoms contain 17 negative electrons (negatively charged particles). These move around the heavy core of the atom in three shells. Within the inner shell there are two electrons, within the middle shell there are eight and within the outer shell there are seven. In the outer shell there is space left for another electron. This causes free, charged atoms, called ions, to form. It can also cause an extra eletron to form (a covalent bond; a chlorine bond), causing the outer shell to complete.
Where can chlorine be found?
Chlorine can be found on many different locations all over the world. Chlorine is always found in compounds, because it is a very reactive element. Chlorine can usually be found bond to sodium (Na), or in kitchen salt (sodium chloride; NaCl). Most chlorine can be found dissolved in seas and salty lakes. Large quantities of chlorine can be found in the ground as rock salts or halite.
The properties of chlorine
Chlorine (Cl2) is one of the most reactive elements; it easily binds to other elements. In the periodic chart chlorine can be found among the halogens.
Other halogens are fluorine (F), bromine (Br), iodine (I) and astatine (At). All halogens react with other elements in the same way and can form a large quantity of substances. Halogens often react with metals to form soluble salts.
Chlorine atoms contain 17 negative electrons (negatively charged particles). These move around the heavy core of the atom in three shells. Within the inner shell there are two electrons, within the middle shell there are eight and within the outer shell there are seven. In the outer shell there is space left for another electron. This causes free, charged atoms, called ions, to form. It can also cause an extra eletron to form (a covalent bond; a chlorine bond), causing the outer shell to complete.
Chlorine
can form very stable substances, such as kitchen salt (NaCl). Chlorine can also
form very reactive products, such as hydrogen chloride
(HCl). When hydrogen chloride dissolves in water it becomes hydrochloric acid.
The hydrogen atom gives off one electron to the chlorine atom, causing hydrogen
and chlorine ions to form. These ions react with any kind of substance they
come in contact with, even metals that are corrosion resistant
under normal circumstances. Concentrated hydrochloric acid can even
corrode stainless steel. This is
why it is stored either in glass or in plastic.
How is chlorine transported?
Chlorine is a very reactive and corrosive gas. When it is transported, stored or used, safety precautions must be taken. In Holland for example, chlorine is transported in separate chlorine trains.
How can chlorine be stored?
Watery chlorine should be protected from sunlight. Chlorine is broken down under the influence of sunlight. UV radiation in sunlight provides energy which aids the break-down of underchloric acid (HOCl) molecules. First, the water molecule (H2O) is broken down, causing electrons to be released which reduce the chlorine atom of underchloric acid to chloride (Cl-). During this reaction an oxygen atom is released, which will be converted into an oxygen molecule:
2HOCl -> 2H+ + 2Cl- + O2
How is chlorine produced?
Chlorine is produced from chlorine bonds by means of electrolytic or chemical oxidation. This is often attained by electrolysis of seawater or rock salt. The salts are dissolved in water, forming brine. Brine can conduct a powerful direct current in an electrolytic cell.
Because
of this current chlorine ions (which originate from salt dissolving in water)
are transformed to chlorine atoms. Salt and water are divided up in sodium hydroxide
(NaOH) and hydrogen gas
(H2) on the cathode and chlorine gas on the anode. These cathode and
anode products should be separated, because hydrogen gas reacts with chlorine
gas very agressively.
Chlorine
applications
Chlorine is applied on a massive scale. Chlorine is a very reactive element, causing it to quickly form compounds with other substances. Chlorine also has the ability to develop a bond between two substances that do not normally react with one another. When chlorine bonds to a substance that contains carbon atoms, organic substances are formed.
Chlorine is applied on a massive scale. Chlorine is a very reactive element, causing it to quickly form compounds with other substances. Chlorine also has the ability to develop a bond between two substances that do not normally react with one another. When chlorine bonds to a substance that contains carbon atoms, organic substances are formed.
Examples
are plastic, solvents and oils, but also several human body fluids. When
chlorine chemically binds to other elements, it often replaces a hydrogen atom
during a so-called substitution reaction. Multiple hydrogen atoms in the same
molecule can be replaced by chlorine atoms, causing new substances to form one
after another.
Chlorine plays an important role in medical science. It is not only used as a disinfectant, but it is also a constituent of various medicines. The majority of our medicines contain chlorine or are developed using chlorine-containing byproducts. Medical herbs also contain chlorine. The first anaesthetic used during surgery was chloroform (CHCl3).
The chemical industry creates ten thousands of chlorine products using a small number of chlorine containing chemicals. Examples of products which contain chlorine are glue, paints, solvents, foam, rubbers, car bumpers, food additives, pesticides and antifreeze.
One of the most commonly used chlorine-containing substances is PVC (poly vinyl chloride). PVC is widely used, for example in drainpipes, insulation wires, floors, windows, bottles and waterproof clothes.
Chlorine plays an important role in medical science. It is not only used as a disinfectant, but it is also a constituent of various medicines. The majority of our medicines contain chlorine or are developed using chlorine-containing byproducts. Medical herbs also contain chlorine. The first anaesthetic used during surgery was chloroform (CHCl3).
The chemical industry creates ten thousands of chlorine products using a small number of chlorine containing chemicals. Examples of products which contain chlorine are glue, paints, solvents, foam, rubbers, car bumpers, food additives, pesticides and antifreeze.
One of the most commonly used chlorine-containing substances is PVC (poly vinyl chloride). PVC is widely used, for example in drainpipes, insulation wires, floors, windows, bottles and waterproof clothes.
Chlorine-based
bleach is applied as a disinfectant on a large scale. The substances are also
used to bleach paper. Bleaching occurs as a result of chlorine or hypochlorite
oxidation.
About 65% of industrialized chlorine is used to produce organic chemicals, such as plastics. About 20% is used to produce bleach and disinfectants. The remaining chlorine is used to produce inorganic compounds from chlorine and several different elements, such as zinc (Zn), iron (Fe) and titanium (Ti).
About 65% of industrialized chlorine is used to produce organic chemicals, such as plastics. About 20% is used to produce bleach and disinfectants. The remaining chlorine is used to produce inorganic compounds from chlorine and several different elements, such as zinc (Zn), iron (Fe) and titanium (Ti).
Chlorine as a bleach
Surfaces can be disinfected by bleaching. Bleach consists of chlorine gas dissolved in an alkali-solution, such as sodium hydroxide (NaOH). When chlorine is dissolved in an alkalic solution, hypochlorite ions (OCl-) are formed during an autoredox reaction. Chlorine reacts with sodium hydroxide to sodium hypochlorite (NaOCl). This is a very good disinfectant with a stable effect.
Surfaces can be disinfected by bleaching. Bleach consists of chlorine gas dissolved in an alkali-solution, such as sodium hydroxide (NaOH). When chlorine is dissolved in an alkalic solution, hypochlorite ions (OCl-) are formed during an autoredox reaction. Chlorine reacts with sodium hydroxide to sodium hypochlorite (NaOCl). This is a very good disinfectant with a stable effect.
Bleach cannot be combined with acids. When bleach comes in contact with acids the hypochlorite becomes instable, causing poisonous chlorine gas to escape. The accompanying underchloric acid is not very stable.
source: lenntech.org
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