Chemistry of Chlorine
Chlorine is a halogen in row 17 and period 3. It is very reactive and is widely used for many purposes, such as as a disinfectant. Due to its reactivity, it is commonly found in nature bonded to many different elements.
At room temperature, pure chlorine is a yellow-green gas. Chlorine is easily reduced, making it a good oxidation agent. By itself, it is not combustible, but many of its reactions with different compounds are exothermic and produce heat. Because chlorine is so highly reactive, it is found in nature in a combined state with other elements, such as NaCl (common salt) or KCl (sylvite). It forms strong ionic bonds with metal ions. Since it is a halogen, chlorine exists as Cl2, a nonpolar diatomic molecule with a low boiling point.
Reactions Involving Chlorine
Chlorine is highly reactive with many different elements and compounds
Usually, reactions of chlorine with water are for disinfection purposes. Chlorine is only slightly soluble in water, with its maximum solubility occurring at 49°F. After that, its solubility decreases until 212°F. At temperatures below that range, it forms crystalline hydrates (usually Cl2).
H2O) and above it, it becomes insoluble. Between that range, it usually forms hypochlorous acid (HOCl). This is the primary reaction used for water/wastewater disinfection and bleaching.
Cl2+H2O → HOCl + HCl
At the boiling temperature of water, chlorine decomposes water
2Cl2+2H2O → 4HCl + O2
Although chlorine usually has -1 oxidation state, it can have oxidation states of +1, +3, +4, or +7 in certain compounds, such as when it forms Oxoacids with the alkali metals
When H2 and Cl2 are exposed to sunlight or high temperatures, they react quickly and violently in a spontaneous reaction. Otherwise, the reaction proceeds slowly.
H2+Cl2 → 2HCl
HCl can also be produced by reacting Chlorine with compounds containing Hydrogen, such as Hydrogen sulfide
Chlorine, like many of the other halogens, can form interhalogen compounds. Examples include BrCl, ICl, ICl2. The heavier elements in one of these compounds acts as the central atom. For Chlorine, this occurs when it is bounded to fluorine in ClF, ClF3, and ClF5
Chlorine reacts with most metals and forms metal chlorides, with most of these compounds being soluble in water. Examples of insoluble compounds include AgCl and PbCl2. Gaseous or liquid chlorine usually does not have an effect on metals such as iron, copper, platinum, silver, and steel at temperatures below 230°F. At high temperatures, however, it reacts rapidly with many of the metals, especially if the metal is in a form that has a high surface area (Such as when powdered or made into wires).
Example: Chlorine oxidizing iron
Cl2+Fe → FeCl2
Fe → Fe+2 +2e
Cl2+2e- → 2Cl-
Cl35 and Cl37 are the two natural, stable isotopes of Chlorine. Cl36, a radioactive isotope, occurs only in trace amounts as a result of cosmic rays in the atmosphere. Chlorine is usually a mixture of 75% Cl35 and 25% Cl37. Besides these Chlorine-35/36/37, the other isotopes must be artificially produced. A table containing some common isotopes is found below:
Production and Uses
Chlorine is a widely used chemical with many applications.
Chlorine is used in the disinfection (removal of harmful microorganisms) of water and wastewater. In the United States, it is almost exclusively used. Compared to other methods, it is effective at lower concentrations, and is inexpensive. Chlorine was first used to disinfect drinking water in 1908, using sodium hypochlorite (NaOCl):
NaOCl+ H2O → HOCl+NaOH
Following widespread use of sodium hypochlorite to disinfect water, diseases caused by unclean water decreased greatly. Disinfection is usually split into two stages; the first being the initial treatment that destroys and prevents the growth of algae and bacteria, and the second involving leaving some active agent that continues to prevent harmful pathogens from growing again.
PVC(Polyvinyl Chloride) is a plastic which is widely manufactured throughout the globe, and is responsible for nearly a third of the world’s use of chlorine. It is usually manufactured by first taking EDC(ethylene dichloride) and then making it into a vinyl chloride, the basic unit for PVC. From then on, vinyl chloride monomers are linked together to form a polymer. PVC becomes malleable at high temperatures, making it flexible and ideal for many purposes from pipes to clothing. However, PVC is toxic. When in gaseous form and inhaled, it can cause damage to the lungs, the body’s blood circulation, and nervous system. The production of PVC has many regulations surrounding it due to the many harmful effects that the plastic itself and the intermediates involved have on the environment and on human health.
Paper is one of the most widely consumed products in the world. Before wood is made into a paper product, however, it must be turned into pulp (separated fibrous material). This pulp has a color that ranges from light to dark brown. Chlorine is used to bleach the pulp to turn it into a bright, white color, which makes it desirable for consumers. The process usually involves a number of steps, depending on the nature of the pulp.
1) Solve and balance the following equations
2) Write the electron configuration for Chlorine.
3) What is the molecular geometry of the following? (See Valence Bond Theory)
4) What are the naturally occurring Chlorine isotopes?
5) When does Chlorine have an oxidation state of +5?
1) Solve and balance the following equations:
a) H2S + 4Cl2 + 4H20 --> H2S04 + HCl
b) 2Sb + 3Cl2 +H20 > 2SbCl3
2) The electron configuration of Chlorine is: 1s22s22p63s23p5
3) What is the molecular geometry of the following?
a) ClO2 -Bent or angular; ClO2 is bonded to two ligands, has one lone pair and one unpaired electron.
b) ClF5 -Square pyramid; ClO2 is bonded to five ligands and has one lone pair
4) The naturally occurring Chlorine isotopes are Chlorine-35 and Chlorine-36. While Chlorine-37 does occur naturally, it is radioactive and unstable.
5) Chlorine has an oxidation state of +5 when it reacts with oxoacids with the Alkali Metals.
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