Chlorine preparation and properties, Group 17 P Block Elements
→ The first isolated halogen, was discovered by Scheele in 1774. He discovered it by the action of HCl on MnO2. In 1810. Davy described its elementary nature and he suggested the name chlorine on behalf of its colour.
→ Chlorine is a Greek word taken from chlorous meaning yellowish green. In 1785, Berthollet put its technical use. Chlorine is widely distributed in the form of chlorides of different metals in nature. One of the common example of it is common salt (NaCl).
Chlorine is highly reactive no it does not occur in native state. About 0.19% part of lithosphere is constituted by it. In nature it occurs mainly in the form of chlorides of sodium and other alkali as well as alkaline earth metals. The most abundant compound of chlorine is common salt (NaCl). NaCl is found in saline Inkes, brines, oceans etc. Other minerals of chlorine Are Carnallite (KCl. MgCl2 . 6H2O), Sylvine (KCl) etc.
Some important method of preparations of chlorine are as follows:
→ By manganese dioxide: When manganese dioxide is heated with concentrated hydrochloric acid then chlorine is prepared.
MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O
→ If manganese dioxide is heated with common salt and concentrated H2 SO4 then chlorine is prepared.
4NaCl + MnO2 + 4H2SO4 → MnCl2 + 4NaHSO4 + 2H2O + Cl2
→ By potassium permanganate : When potassium permanascanate is beated with hydrochloric acid (HCl) chlorine gas is formed.
→ By Potassium dichromate : When potassium dichromate to beated with hydrochloric acid then chlorine gas is formed.
K2Cr2O7 + 14HCl 2KCl + 2CrCl3+ 3Cl2 + 7H2O
By lead oxides. When lead oxide reacts with hydrochloric acid then chlorine gas is formed.
→ By Bleaching Powder By the action of HCl on bleaching powder chlorine is formed:
Commercial manufacturing of chlorine i Commercially chlorine gas can be manufactured by the following process:
→ Deacon’s process: In this procesa hydrochloric acid is oxidised by atmospheric air in the presence of Cuci, catalyst at 723 K temperature.
→ The above method is now modified by using improved catalvat Cuci with didymium oxide as promoter; didymium is old name whose meaning is in’ bere two lanthanoidsie.praseodymium and neodymium is used simultaneously.
→ Electrolytic process: By the electrolysis of brine soulution (sodium chloride solution) chlorine is obtained as by product at anode.
It can also be obtained as a by product during the manufacturing of sodium by electrolysis of fused NaClin Down’s Process
Physical Properties of Chlorine
- It has pungent and suffocating odour
- It is a greenish yellow gas.
- It is about 2.5 time heavier than air.
- It can easily be liquified into greenish yellow liquid. Its boiling point is 239 K.
- It is soluble in water, It forms chlorine water which is a strong excidising agent.
- It is poisonous in nature. If it is inhaled in small quantity then it causes headache. If it is inhaled in large quantity then it may prove to be deadly
- Its meling point is 171K.
Chemical properties of Chlorine
Its important chemical properties are as follows:
→ Action on litmus. There is no effect of dry chkirine on litmus paper but moist chlorine may turn blue litmus red which is due to the presence of HCl and HClO in it.
→ Affinity for hydrogen : It does not combine with hydrogen in dark but in presence of sunlight it combines with hydrogen explosively.
→ Reaction with water: Since it has great affinity for bydrogen hence it decomposes water in presence of sunlight to produce HCl.
→ Reaction with ammonia : It reacts with ammonia in two ways
When ammonia is taken in exces, then nitrogen is formed
When chlorine is taken in excess, then nitrogen trichloride is formed.
Reaction with Metals :
→ With very active metals like sodium, chlorine etc. it burn in the atmosphere of chlorine to form their chlorides.
- 2Na + Cl2 → 2NaCl
- Ca + Cl2 → CaCl2
→ With less active metals like iron, aluminium, zinc, copper etc it reacts only on heating
Reaction with Alkalies Chlorine reacts with alkalies in different ways.
→ With cold and dilute With Cold and dilute alkalier. chlorine reacts to form chlorides and hypochlorites.
→ with hot and concentrated With hot and concentrated alkalies, chlorine forms chlorides and chlorates.
The above reaction is disproportionate reaction
Reaction with slaked lime: Chlorine reacts with it in two ways
→ With cold slaked lime, chlorine forms calcium hypochlorite Ca(OCl)2
→ With dry slaked lime, it produces bleaching power.
→ Reaction with hot and conc. slaked lime :
6Ca(OH)2 + 6Cl2 → 5CaCl2 + Ca(ClO3)2 + 6H2O
→ Reaction with hydrocarbons : Chlorine reacts with hydrocarbons. It show substitution reaction with saturated hydrocarbons and show addition reaction with unsaturated hydrocarbons.
→ Bleaching action : Chlorine can bleach natural colouring material like flowers creen leaves, indigo etc, in presence of water. The bleaching action of chlorine is due to its ability to oxidine coloured material into colourless material. The related reaction is as follows:
- Cl2 + H2O → 2HCl + [O]
- Coloured material + [O] → Colourless material
→ The bleaching action of chlorine is by oxidation hence it is permanent. Chlorine beaches only in presence of waterthus, dry chlorine cannot bleach dry flowers due to the absence of water. Its bleaching action is harmful because during bleaching hydrochloric acid (HCI) is formed thus, the deliente fibers are likely to be destroyed by HCI. That is why, chlorine la used only for bleaching wood palp, paper pulp and clothes etc.
→ Addition Reactions. Chlorine also show addition reactions
→ Reaction with other halogens: Chlorine can react with other halogen forming interhalogen compounds.
→ Reaction with non metals : Non metals like sulphur, phosphorus etc. can also react with chlorine.
→ Reaction with metalloids: Chlorine also recta with metalloids like As, Sh etc
→ Reaction with halides: Chlorine can replace less electronegative halogens from their halides
2KBr + Cl2 → 2KCl + Br2
2KI + Cl2 → 2KCl + I2
→ As oxidising agent : In presence of moisture chlorine behaves as strong oxidising agent. The yellow colour of chlorine is disappeared due to the formation of HCL and HOCl, HOCl form nascent oxygen which is responsible for the oxidising properties of chlorine.
→ Some important oxidising reactions of Cl2 are as follows:
→ In some reactions chlorine enn lo act as an oxidising agent in absence of water.
It oxidises ferrous chloride into ferric chloride.
Use of Chlorine
- Used industrially for blenching wood pulp. It is also used in bleaching cotton, wood, textiles, paperete.
- It is used in extraction of gold and platinum
- It is used in manufacturing of dyes, drugs and organic compounds like CCl4 CHCl3, DDT, refrigerants etc.
- It is used in manufacturing chlorates which are used in flashlight powder matches and explosive ete.
- It is used in manufacturing the poisonous gases like phogene (COCl2), tear gas (CCl3NO2) and mustard gas (ClCH2CH2SCH2CH2Cl).
- It is used in sterilising the drinking water
- Used as germicides and insecticides