| OXIDATION-REDUCTION-OXIDES-TYPES OF OXIDES |
| |
OXIDATION
| |
| The process of oxidation may be defined by the following ways: |
|  A chemical reaction in which oxygen combines with other elements to produce oxides is called oxidation.
FOR EXAMPLE: |
|
|
2NO + O2  2NO2
C + O2 CO2
2SO2 + O2  2SO3
|
| OR |
| Removal of hydrogen from its compounds is also called Oxidation. |
MnO2 + 4HCl MnCl2 + 2H2O + Cl2
|
| OR |
| Loss of electron from an element is called oxidation. |
Na Na+ + e-
|
|
REDUCTION
| |
| Reduction may be defined as: |
| Removal of oxygen from a substance is called reduction . |
CuO + H2 Cu+H2O
|
| OR |
| Addition of hydrogen in a substance is called Reduction. |
| OR |
| Gain of electron is called Reduction. |
Na+ + e- Na
|
OXIDES-TYPES OF OXIDES
|
|
OXIDES
| |
The binary compounds of oxygen are known as "OXIDES".
OR
Binary compounds of different elements in which one element is oxygen are known as "oxides".
|
TYPES OF OXIDES
| |
| Depending upon the oxidation state of oxygen in a binary compound, oxides are divided into the following classes: |
NORMAL OXIDES
| |
Those oxides in which oxidation state of oxygen is (-2) are known as normal oxides.
FOR EXAMPLE:MgO, SO2, CO2 , |
PEROXIDES
| |
| Those oxides in which oxidation state of oxygen is (-1) are known as peroxides. |
| FOR EXAMPLE:H2O2, Na2O2, BaO2 |
SUPEROXIDES
| |
| Those oxides in which oxidation state of oxygen is (-1/2) are known as superoxides. |
FOR EXAMPLE:
KO2, RbO2 |
SUBOXIDES
| |
| those oxides which have less quantity of oxygen than the normal oxides are known as suboxides. They are unstable and very limited in quantity. |
FOR EXAMPLE:
C3O2 (Carbon suboxides) |
TYPES OF NORMAL OXIDES
| |
There are three types of normal oxides:BASIC OXIDES
ACIDIC OXIDES
NEUTRAL OXIDES
AMPHOTERIC OXIDES |
BASIC OXIDES
| |
| Normal oxides formed between metals and oxygen are known as Basic Oxides. These oxides have basic character . |
4Na + O2 2Na2O
|
ACIDIC OXIDES
| |
| Normal oxides form between nonmetals and oxygen are known as acidic oxides .These oxides have acidic character . |
S+O2 SO2
C+O2 CO2
|
NEUTRAL OXIDES
| |
Neutral oxides are those oxides which in contact with water produce neither an acid nor a base. I mean to say that the aqueous solution of these oxides have a neutral character.
FOR EXAMPLE:H2O, NO, N2O |
AMPHOTERIC OXIDES
| |
| These are the oxides of certain metals such aluminuim, zinc and tin which posses dual properties of an acid and a base. |
2Zn + O2 2ZnO
4Al+3O2 2Al2O3 Extraction of sulphur by Frasch Method
| sulphur is extracted by HERMAN FRASCH METHOD |
PRINCIPLE
| |
| The basic principle of Frasch Method is that sulphur is melted underground and pumped up to the surface of the earth. |
|
DETAILS OF PROCESS
| |
|
|
SYSTEM CONFIGURATION
| |
| A bore is made to the underground deposits of sulphur and three concentric pipes are sunk into the bore. |
|
OUTER PIPE
| |
| The outer most pipe has diameter of 20 cm is sunk upto the deposits .This pipe is an inlet for super heated water. |
MIDDLE PIPE
| |
| The 2nd pipe of 10 cm diameter is held a little above the surface of sulphur deposits. This pipe is outlet for molten sulphur. |
INNER PIPE
| |
| The inner most pipe is used to blow hot compressed air into the deposits of sulphur. |
|
METHOD
| |
Superheated steam at 170oC under 16 atmp is pumped down the outer most pipe . Since melting point of sulphur is 113oC , it is melted and collects at the bottom. Hot compressed air is blown down the inner most pipe to produce foam of molten sulphur . This foam rises through the annular space between the inner most pipe and the next. The foam of sulphur is collected in wooden tubs. After few hours, sulphur is converted into solid blocks.
|
|
On industrial scale, sulphuric acid can be prepared by the following two methods.
 Contact process
Lead Chamber process
|
CONTACT PROCESS
| |
Now a days, sulphuric acid is prepared by contact process all over the world.
Preparation of sulphuric acid by contact process is based upon the catalytic oxidation of SO2 to SO3. |
|
DETAILS OF
CONTACT PROCESS
| |
Following steps are involved in the preparation of H2SO4.
PREPARATION OF SO2.
PURIFICATION OF SO2.
OXIDATION OF SO2.
ABSORPTION OF SO3.
DILUTION OF OLEUM. |
|
| |
|
PREPARATION OF SO2
| |
SO2 is obtained by burning sulphur or by heating iron pyrite (FeS2) in pyrite burner.
S + O2 èSO2
4FeS2 + 11O2 è2Fe2O3 + 8SO2 |
PURIFICATION OF SO2
| |
SO2 contains a number of impurities such as dust particles, Arsenous oxide, vapours, sulphur etc. These impurities must be removed otherwise catalyst loses its efficiency (catalyst poisoning).
DUST CHAMBER:
SO2 is first passed through the dust chamber where steam is spread over the gas to remove dust particles, which settle down. Fe(OH)3 also sprayed over to remove oxides of Arsenic.
WASHING TOWER:
SO2 is then passed through a washing tower after cooling. Here it is sprayed by water to remove any other soluble impurities.
DRYING TOWER:
The gas is now dried by passing through drying tower where conc. H2SO4 (dehydrating agent) is sprayed. H2SO4 removes moisture from SO2.
TYNDALL BOX (TEST BOX):
Arsenic oxide is a poison for the catalyst. It is removed when the gas is passed over ferric hydroxide.
As2O3 + 2Fe(OH)3 è 2FeAsO3 + 3H2O. In order to remove traces of As2O3, it is passed through a test box, where a strong beam of light is thrown against the gas. If there is no scattering of light in the box, it indicates that gas is free from As2O3.
|
|
OXIDATION OF SO2 TO SO3
| |
CONTACT TOWER:
Oxidation of SO2 is carried out in contact tower where V2O5 is filled in different pipes. SO2 here reacts with air (O2) to produce SO3. Under above conditions 98% SO2 is converted into SO3.
2SO2 + O2 è 2SO3 + 45Kcal
CONDITIONS NECESSARY FOR MAXIMUM YIELD OF SO3:
Oxidation of SO2 is a reversible and exothermic process in which volume of product is less than the volumes of reactants. In order to obtain maximum amount of SO3, according to Le-Chatelier’s Principle following conditions are necessary.
CONCENTRATION:
Excess of O2.
TEMPEATURE:
A decrease in temperature favours reaction in forward direction. Optimum temperature for this process is 450oC to 500oC.
PRESSURE:
Since volumes of reactants are greater than the product (3:2), therefore, according to Le-Chatelier’s Principle a high pressure is favourable. Optimum pressure is about 1.5 to 1.7 atmosphere.
USE OF CATALYST:
At low temperature, rate of reaction decreases. To increase rate of reaction a catalyst vanadium pentaoxide (V2O5) is used. |
ABSORPTION OF
SO3 IN H2SO4
| |
SO3 is not directly passed in water, because a dense fog of minute particles of H2SO4 is produced. It is therefore, dissolved in conc.H2SO4 to form pyrosulphuric acid (oleum).
SO3 + H2SO4 è H2S2O7 (OLEUM) |
DILUTION OF OLEUM
| |
Oleum is now diluted with water to form H2SO4 of required concentration.
H2S2O7 + H2O è 2H2SO4
PROPERTIES OF SULPHURIC ACID
|
|
|
STRUCTURE OF
SULPHURIC ACID
| |
|
|
LABORATORY
GRADE H2SO4
| |
| Laboratory grade sulphuric acid is 98% pure and its density is 1.839 gm/cc. It is used in chemical analysis in laboratories. |
FUMING SULPHURIC ACID
| |
| Sulphuric acid containing 20% SO3 dissolved in it with density 1.929 gm/cc is called fuming sulphuric acid. |
PHYSICAL PROPERTIES
OF H2SO4
| |
| It is a colourless, odourless, viscous oily liquid. Melting point of H2SO4 is 10.5oC. Boiling point is 290oC. It is hygroscopic and corrosive in nature. Soluble in water. It causes severe burns on skin. It can destroy fabrics, paper. |
USES OF H2SO4
| |
It is a very widely used reagent.
In the manufacture of fertilizers, dyes, drugs, paints, explosives.
Petroleum industry, storage batteries.
Cotton industry, paper industry, silk industry, detergents.
Stain remover, pickling of steel.
Dehydrating agent.
Laboratory agent. Laboratory and industrial preparation of chlorine gas
| |
LABORATORY METHOD
|
|
| In laboratory Cl2 gas is prepared by heating a mixture of NaCl , MnO2 with conc. H2SO4. |
4NaCl +4H2SO4 +MnO2è 4NaHSO4 +MnCl2+2H2O +Cl2
|
SECOND METHOD
| |
| Chlorine may also be obtained by heating mangenese dioxide with concentrated hydrochloric acid |
MnO2 + 4HCl è MnCl2+2H2O +Cl2
|
|
INDUSTRIAL PREPARATION
| |
|
| On industrial scale Cl2 is obtained by the electrolysis of aqueous solution of NaCl called Brine. |
|
NaCl + H2O è Cl2+H2 + 2NaOH
|
IONIZATION OF NaCl
|
|
NaCl Na+ + Cl-
|
|
REACTION AT ANODE
| |
| Cl- ions are collected at anode and form chlorine gas |
2Cl-è 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-è 2NaOH + H2
|
OVERALL REACTION
| |
2Na+ + 2H2O + 2e-è 2NaOH + H2
2Cl-è Cl2+ 2e-
|
--------------------------------------
|
2Na+ 2Cl- + 2H2Oè 2NaOH + Cl2 +H2
BLEACHING POWDER
|
Chemical name : Calcium chloro hypo chloride.
Commercial name : Bleaching powder.
Chemical formula : Ca(OCl)Cl.H2O or CaOCl2.H2O. |
| It is a dirty white amorphous powder with pungent smell of chlorine gas. |
Industrial Preparation
of Bleaching Powder
| |
| On industrial scale it is prepared by "Hasen-Clever Method". |
Raw Material
| |
1. Slaked lime Ca(OH)2
2. Chlorine gas |
Hasen-Clever Plant
| |
| The plant consists of four cylinder of castiron. Each cylinder is about 2 to 3m long .Each cylinder is provided with a stirrer to ensure the mixing of substances. There is an inlet in the upper most cylinder for Ca(OH)2. The bottom cylinder has an inlet for Cl2 and outlet for bleaching powder. Each cylinder is connected to the other by means of pipes. |
|
Procedure
| |
| Slaked lime is introduced in the first cylinder with the help of compressed air .Cl2 gas is introduced from the lower most cylinder .In tjis way these two substances meet, when proper saturation is reached, the product is separated from the last cylinder as bleaching powder. |
Ca(OH)2 + Cl2 è Ca(OCl)Cl.H2O
|
Properties
| |
| It is a strong bleaching agent.Due to liberation of chlorine gas in aqueous solution it decolorize different fabrics. It is also an anti-septic. |
Chemical properties
| |
Reaction with water:
Ca(OC)Cl + H2O è Ca(OH)2 + Cl2
With HCl:
Ca(OCl)Cl + 2HCl è CaCl2 + Cl2 + H2O
With CO2:
2Ca(OCl)Cl + CO2 + H2O è CaCO3 + CaCl2 +2HOCl |
Uses
| |
| As oxidizing and bleaching agent it is used in textile and other industries. It is also used in the purification of drinking water. |
|
|
|
|
|
.jpg)
.jpg)
0 comments:
Post a Comment