Tuesday, September 24, 2013

Structure Of Hydrogen peroxide

  • Hydrogen peroxide is a non-linear molecule.
  • It has a non-polar structure of C2  symmetry.
  • O-O bond is a single bond. -O-O- linkage is called peroxy linkage.
The structure is shown below.

Friday, September 20, 2013

Properties Of Hydrogen peroxide ( physical and chemical properties )

Physical Properties:

  • Hydrogen peroxide is a clear and colorless liquid.
  • It has a slightly pungent smell.
  • It is a syrupy liquid in the unhydrous state.
  • It is a diamagnetic.
  • It is miscible with water, alcohol, and ether in all proportion.
  • It is more highly associated via hydrogen bonding than water.
  • Melting point is 273 K.
  • Boiling point is 423 K.
  • Molecular formula 2(HO).

Hydrogen peroxide ( Laboratory Preparation )

  • Hydrogen peroxide was first discovered by Thenard in 1818.
  • Hydrogen peroxide is a clear liquid.
  • Hydrogen peroxide is slightly more viscous than water.
  • It is a strong oxidizer. 
  • In dilute solution it appears colorless.
  • It is used as a bleach or cleaning agent.
  • Traces of hydrogen peroxide are found in atmosphere and in certain plants.
Laboratory Preparation of Hydrogen peroxide: 
             Hydrogen peroxide is prepared by Merck's process. In this method calculated quantities of sodium peroxide to ice cold dilute 20% solution of sulphuric acid. 30% of hydrogen peroxide is obtained by this process.
                        Na2O2     +     H2SO4     →     Na2SO4      +     H2O2
Pure hydrogen peroxide is obtained by reacting BaO2   with an acid.
                        BaO2      +      H2SO4      →     BaSO4         +      H2O2
                      3BaO2      +      2H3PO4     →    Ba3(PO)4      +     3H2O2
Phosphoric acid is preferred to  H2SO4  because soluble impurities like Barium persulphate tends to decompose  H2O2 while  H3PO4  is act as preservative ( negative catalyst ) for hydrogen peroxide. 
Hydrogen peroxide is manufactured by the electrolysis of 50% sulphuric acid followed by vacuum distillation. Here 30% of pure hydrogen peroxide is obtained.

Wednesday, September 18, 2013

Properties of Heavy Water ( Physical, Chemical and Biological )

Physical Properties:

  • Heavy water is colorless, odourless and tasteless mobile liquid..
  • Higher viscosity of heavy water is responsible for lower solubility of ionic solids like NaCl and smaller mobility ions.
Chemical Properties: 
Reaction with Metals:
      Heavy water react slowly with alkali metals and alkaline earth metals to form heavy hydrogen. ( D2 ).
                                   D2O   +   2Na   →   2NaOD   +   D2
                                                         (Sodium deuteroxide)
                                  D2O   +   Ca   →   Ca(OD)2   +   D2

                                                        (Calcium deuteroxide)
Reaction with Metal oxides:
      Heavy water react slowly with metal oxide to form heavy alkalies. ( deuteroxides)
                                  Na2O   +   D2O   →   2NaOD
                                  CaO    +   D2O    →   Ca(OD)2
Reaction with Non-metallic oxides:
       Heavy water react with non-metallic oxides to form deutero acid.
                                 D2O   +   N2O5   →   2DNO3
                                                               (Deuteronitric acid)
                                 D2O   +   SO3   →   D2SO4
                                                              (Deutero sulphuric acid)
                                3D2O   +   P2O5   →   2D3PO4
                                                                (Deuterophosphoric acid)
Electrolysis :
       On electrolysis, heavy water containing dissolved Na2Co3 decomposes into deuterium and oxygen which are liberated at the cathode and anode respectively.
                                    2D2O    →    2D2       +      O2
                                                      (cathode)        (anode)
Deutero hydrates:
          With salt and other compounds they form deuterates.
CuSO4.5D2O,  Na2SO4.10D2O,  NiCl2.6D2O.
 Exchange Reactions:
           When compounds containing hydrogen are treated with D2O  , hydrogen is exchanged by deuterium partially or completely.
                                       NaOH    +    D2O     →    NaOD    +    HDO
                                      NH4Cl    +    4D2O    →    ND4Cl    +    4HDO
                                       HCl        +    D2O      →    DCl       +    4HDO
Raction with Carbide and Nitride:
                                     CaC2    +    2D2O    →    Ca(OD)2    +    DC = CD
                                     Mg3N  +    6D2O     →     3Mg(OD)2    +     2ND3  
                             (Magnesium nitride)                                              (Deuterommonia)
Reaction with Phosphides:                                                                                                                                                            Ca3P2    +    6D2O    →     3Ca(OD)2    +    2PD3
                           (Calcium phosphide)                                         (Deuterophosphine)
                                       Na3As    +    3D2O    →    NaOD    +    AsD3
                            (Sodium arsenide)                                        (Deuteroarsene)
Biological Properties:
  • The tobacco seeds do not grow in heavy water.
  • Pure heavy water kill small fish, tadpoles and mice when fed upon it.
  • Heavy water, retards the growth of living organisms like plants and animals.

Heavy Water ( Preparation - Electrolytic cell Method )

Heavy Water:

  • Heavy water is also called as deuterium oxide or 2H2O or D2O. 
  • The oxide of hydrogen is called heavy water.
  • Heavy water was discovered by Urey in 1932.
  • Heavy water occurs naturally, although it is much less common than regular water.
Preparation of heavy water :

             The main source of heavy water is the ordinary water from which it is isolated. Generally it is prepared by prolonged electrolysis or fractional distillation.

Prolonged Electrolysis Of Ordinary Water:
            This method is involved in multistage electrolysis of ordinary water containing alkali. ( eg. NaOH ). The cylindrical vessels made of steel which act as cathode. The cylindrical sheet of nickel which act as anode with a number of holes punched in it. The electrolysis carried out in different stages. In these stage large number of electrolytic cells are used.

First Stage:
      Thirty electrolytic cells are used in this stage. Each cell is filled with 3% of NaOH solution. The electrolysis is carried out at 72-hrs, in the presence of current at 110 volts.The volume is reduced to 1/6 th of original volume taken.That tome hydrogen and oxygen gases are evolved and discarded. The volume left contains about 2.5 % of heavy water.
Second Stage:
       In this stage 6 electrolytic cells are used. This stage involves the residue left from the first stage. The gases evolved are burnt and water formed return to the first stage cell. The residual liquids contain 12% of heavy water.
Third Stage:
       This stage involve the residue left from the second stage. The gases are burnt and water formed return to the second stage cell. The content of heavy water is raised to about 60%.
Fourth Stage:
       This stage involve the residue left from the third stage. The gases are evolved are burnt as usual and sent to third stage cell. Here nearly 99% of heavy water is obtained.
Fifth Stage:
        99% of heavy water is made free from alkali and other impurities by distillation. Here the gases evolved are  D2  and   O2  are burnt to get 100% pure heavy water.

Monday, September 16, 2013

Ortho and Para hydrogen ( Spin Isomers Of hydrogen )

        The hydrogen molecule contains two atoms, in which the nuclei of both the atoms are spinning. Depending upon the direction of the spin of the nuclei, the hydrogen are of two types.
         The protons in the nuclei of both H-atom spin in same direction is termed as ortho hydrogen.
          The protons in the nuclei of both H-atom spin in opposite direction is termed as para hydrogen.
              In the state of thermal equilibrium at room temperature dihydrogen contains 75% of ortho hydrogen and 25% of para hydrogen. At 25 K, 99% of para hydrogen and 1% of ortho hydrogen. At 0 K hydrogen contains mainly para hydrogen which is more stable. At room temperature the ratio of ortho to para hydrogen is 3:1.
              At low temperature, para hydrogen is favored energetically. The para form was originally prepared by absorbing ordinary hydrogen in activated charcoal in a quartz vessel kept at temperature of 20 K. The charcoal absorb almost pure para hydrogen. By this method pure para hydrogen can be isolated.
               The ortho form was originally prepared at low temperature, the two spin isomers are not equally absorbed on diamagnetic surfaces. Single stage separation of ortho hydrogen on alumina at 77 K, obtain a mixtures of 15 % para hydrogen and 85% of ortho hydrogen.
                Ordinary dihydrogen is an equilibrium mixture of ortho and para hydrogen.

Isotopes of Hydrogen

Isotope :
      Atoms of elements having the same atomic number with different mass numbers are called Isotopes.
      Hydrogen has three naturally occurring isotopes with mass number 1, 2, and 3, each possesing an atomic number of one.

  • Protium or Hydrogen. 1H1    
  • Deuterium or Heavy water. 1H2
  • Tritium. 1H3
Protium Or Hydrogen
  • In chemistry protium is refers to hydrogen -1.
  • Protium is the most common isotope of the element hydrogen. 
  • Protium has one proton, no neutrons, and one electron revolving around it.
  • It constitues 99.98 % of total hydrogen available in nature.
  • It is a stable isotope.
  • Its mass number is one. 
The Structure of protium is given below.

Deuterium Or Heavy water :
  • Deuterium is also known as hydrogen-2 or heavy water. Its symbol is D or 1H
  • Deuterium is otherwise called as deuteron.
  • It contain one proton, one neutron and one solitary electron revolving around the nucleus.
  • It is a stable isotopes.
  • The name deuterium comes from the Greek word 'deutero' which means 'second'. It denote two particles composing the nucleus.
  • Its chemical properties are similar to protium but their reaction rates are different.
  • Its mass number is two.
The structure of Deuterium is given below.

  • Tritium is also known as hydrogen-3. Its symbol is T or 1H
  • Its otherwise called as Triton.
  • It contain one proton and two neutrons.
  • It occurs in the upper atmosphere only were it is continuously formed by nuclear reactions induced by cosmic rays.
  • The name Tritium comes from the Greek word 'tritos' meaning "third".
  • Its mass number is three.
  • Tritium has a half-life of 12.3 years and emits a very weak beta ( ᵝ ) particle.
The structure of Tritium is given below.

Friday, September 13, 2013

Spin quantum number

            Spin quantum number is fourth set of quantum number. It is indicated the orientation of the intrinsic angular momentum of electron in an atom. It is denoted by  ms . There are only two values for s + ½   and s - ½    . These are also referred to as 'spin up' and 'spin down'. The electron in the atom rotates not only around the nucleus but also around its own axis and two opposite direction of rotation are possible ( clockwise and anticlock wise). 

Magnetic quantum number

              The magnetic quantum number is the third set of quantum numbers which describe the unique quantum state of an electron. It is denoted by letter ml . The magnetic quantum number denotes the energy levels available with in a subshell.  ml  can take value from -l to +l.

  • l=0 . s orbital has only one subshell. Therefore the ml of an electron in an s orbital will always be 0 ( m=0 ).
  • l=1. p orbital has three subshells. Therefore the ml of an electron in an p orbital will be           ml = -1,0,+1. This would represents the three different orientations in p orbital. They are usually defined as px, py, pz.
  • l=2. f orbital has five subshell. Therefore the ml of an f orbital will be  ml = -2, -1, 0, +1, +2

Azimuthal quantum number

               Azimuthal quantum number is describes the shape of the orbitals. It is denoted by 'l', is the quantum number associated with the angular momentum of an atomic electron. ( It describes the subshell energy level ). Orbitals have shapes that are best described as spherical ( l=0 ), the polar ( l=1) and cloverleaf (l=2). The values of l ranges from 0 to n-1.
                           l = 0,1,2,3,......n-1
l=0 is called s orbital.
l=1 is called p orbital.
l=2 is called d orbital.
l=3 is called f orbital.
If n=1, l=0 ( 1 sub level ) s orbital.
   n=2, l=0 and 1 ( 2 sub level ) p orbital.
   n=3, l=0,1 and 2 ( 3 sub level ) d orbital.
   n=4, l=0,1,2 and 3 ( 4 sub level ) f orbital.
The energy of the subshell increases with       ( s á  p á  d á  f ).
Azimuthal quantum number otherwise known as subsidiary or angular quantum number or orbital quantum number.

Principle quantum number

               The principal quantum number has the greatest effect on the electron shell or energy level of an atom. It has only positive integer value. It is denoted by 'n'. n can have values 1,2,3,4.. etc. The first level is also known as K level. Second as L level. Third as M level. Forth as N level and so on. The first K level is nearest to the nucleus and next one is second and so on. Principal quantum number is cited first in the set of four quantum numbers associated with an electron.It describe the size of the orbital. It measures the average distance of the electron from the nucleus, 'n' increases the orbital becomes larger and the electron farther from the nucleus.
For example; A hydrogen atom with n=1 the electron is in its ground state if the electron is in the n=2 orbitals , it is an excited state. The total number of orbitals for a given n value is n2.

Quantum Number

           Quantum number describe the distribution of electrons in the atom. In atom large number of electron orbitals are permissible. An orbital of smaller size means there is more chance of finding the electron near the nucleus. These orbitals are designated by a set of numbers known as quantum numbers. Three coordinates that come from Schrodinger's wave equations are principal (n), angular (l) and magnetic quantum numbers. These quantum numbers describe the size, shape and orientation in space of orbitals on an atom. The property of an atoms electronic configuration are described by four quantum numbers given below.

  • Principal quantum number ( n )
  • Azimuthal quantum number ( l )
  • Magnetic quantum number ( ml )
  • Spin quantum number ( ms )
Note :

  • n can have whole number values 1, 2, 3,.....
  • For every value of n and l can have integer values 0 to n-1.
  • m can have any whole number value, -l to +l.
  • s can be ± ½ .

Thursday, September 12, 2013

Chemical Method ( Leaching )

             In this process the ore is washed with some suitable reagent ( solvent ) So the main metal passes into its salt solution. This solution is separated and subjected to further treatment like precipitation. It is then treated further to recover the metal. This is chemical process.
Example :   Aluminium Extraction ;
   Bauxite ore is treated with NaOH, The Al2O3  goes into the solution to form sodium meta-aluminate. The Sodium meta aluminate contain undissolved impurities like SiO2 , Fe2O3 , Fe(OH)3    
  etc. Which are then filtered off.
                                   Al2O3 + 2NaOH        →  2NaAlO2  +  H2O
                                                                     (In solution Form)
The filtrate on dilution, and stirring gives a precipitate of aluminium hydroxide, which is filtered and ignited to get pure alumina.
                                  NaAlO2  + 2 H2O      →    Al(OH)3    +   NaOH     
                                    2  Al(OH)3         Δ→    Al2O3      +   3 H2O

Electromagnetic Separation Process

               This method is meant for separating magnetic impurities from non-magnetic ore particles. Example: Pyrolusite, Chromite, and tinstone. In which tinstone is non-magnetic; while impurities ion, manganese and tungstates are magnetic. The powdered ore is dropped on the conveyer belt moving over electromagnetic roller. The magnetic impurities fall from the belt in a heap near the magnet due to attraction. The non-magnetic concentrated ore falls in separate heap away from the magnet, due to the influence of centrifugal force.

Forth Floatation Process

                 This method is especially suitable for sulphide ores like zinc blende ( ZnS ), and copper pyrites. In this process a mixture of water , pine oil, detergent and powdered ore is taken in a tank. The whole mixture is then stirred vigorously by blowing compressed air. The oil forms a forth (foam) with air. The sulphide ore particles are wetted and rise up along with the forth. ( sulphides are more electronegative so it attracted by covalent oil molecules. The gangue particles wetted by water sink to the bottom of the tank. (The gangue particles are less electronegative so it attracted by water). The forth containing the sulphide ore is skimmed off, collected and allowed to subside, washed and dried to get concentrated ore. The forth flotation process is shown in the following figure.

Gravity Separation Process

             In this method, the powdered ore is placed on a sloping platform and a jet of water is allowed to flow over it. The lighter sandy particles, impurities are washed away, and the denser settles in the groove. This method is especially suitable for heavy oxide ores of haematite, tinstone, ion etc. The gravity separation process is shown in the following figure.

Wednesday, September 4, 2013

General Rules For Assigning Oxidation State

  • The oxidation State ( OS) of fluorine is always -1 in all its compound, since it has the highest electronegativity of all reactive elements.
  • The OS of hydrogen is +1 in all its compound except in metal hydrides. Like NaH, LiH , in these compounds containing elements that are less electronegative than hydrogen. So this compounds contain OS of hydrogen is -1.
  • Oxygen has an OS of -2 . Peroxides like H2O2, BaO2 etc its OS is -1.
  • Alkali metals have an oxidation state of +1 ( except alkalide ).
  • Halogens other than fluorine have an OS of -1. OS of chlorine in chloromonofluoride ( ClF ) is +1. In Brominemonochloride (BrCl) OS is -1 .
  • Alkaline earth metals have an OS of +2.
    The sum of OS in a polyatomic ion is equal to the charge of the ion.Example . The sum of OS for 
    SO42-  is -2.
  • The OS of all the atoms in neutral molecule is zero.
  • The OS of the elements in monoatomic ion is equal to the charge on the ion.
  • The OS of free elements is always zero. Eg. The atoms in He and N2  have OS of 0 ( zero ).
  • In binary compounds metal atom has positive OS and non-metals has negative OS. Example, KI.  Oxidation state of K is +1. Oxidation of I is -1.

  • The convention is that the cation is written first in a formula followed by the anion. Example, NaH   the H is   H-.                Hcl the H is  H+.

Oxidation State Definition

                Oxidation number of the element is defined as the residual charge which its atom has or appears to have when all other atoms from the molecules are removed as ion. In ions the oxidation state is the ionic charge. In covalent compounds the oxidation state corresponds to the formal charge. In elements the oxidation state is zero.
In NaCl the oxidation states are Na (+1) and Cl (-1).
In CCl4 the oxidation states are C (+4) and Cl (-1).
Note :
The oxidation is the difference between the number of electrons associated with an atom in a compound as compared with the number of electrons in an atom of the elements.

Electronic Concept Of Oxidation And Reduction

Oxidation :
       Oxidation is a process in which an atom taking part in chemical reaction loses one or more electrons. Te loss of electrons results in the increase of positive charge ( or ) decrease of negative of the species.
Example :
               Mg         →   Mg2+   +   2e-   ( increase of positive charge )
               Fe2+       →  Fe3+    +   e-       ( increase of positive charge ) 
                Cu        →  Cu2+    +   2e-   ( increase of positive charge ) 
              S2-          →    S      +     2e-     ( decrease of negative charge )

               MnO42-  →   MnO4-   +  e  ( decrease of negative charge ) 
  • Loss of electrons during the reactions are called reducing agents or reductants. In the above equation Mg  , Fe2+  ,  Cu are reducing agents.  
  • Some important oxidizing agents are,  O2 , O3 , H2O2 , Cl2 , HNO3 , KMnO4 ,  etc.

Reduction :
      Reduction is a process in which atom taking part in chemical reaction gains one or more electrons. The gain of electrons results on the decrease of positive charge or increase of negative charge of the species.
Example :

                  Fe3+    +   e-      →   Fe2+      ( Decrease in positive charge )
                  Zn2+   +    2e-   →  Zn           ( Decrease in positive charge )
                   Sn4+   +   2e-   →  Sn2+         ( Decrease in positive charge )  
                       S   +     2e-  →  S2-           ( Increase in negative charge )
                   MnO4-   +  e  → MnO42     ( Increase in negative charge )
  • Gain of electrons during the reactions are called oxidizing agents or oxidants. Sn4+  ,  Zn2+ , Fe3+    are  oxidizing agents.
  • During oxidation acidic nature increases.
  • Burning of coal, rusting of ion and combustion reactions involve oxidation.
  • Just reverse process occurs during reduction. 
  • Some important reducing agents are , H2 , C , H2S , SO2 , SnCl2 , Al, etc.

Sunday, September 1, 2013

Redox Reactions

                      Any chemical reaction in which the oxidation states of the atoms are changed is an oxidation-reduction reaction.This reactions are also known as redox reactions. Redox reactions involve the transfer of electrons between species. Industrial process of electroplating, Extraction of aluminium and sodium metals, manufactures of caustic soda, etc are also based upon the redox reactions. Redox reactions are also form the basis of electrochemical and electrolytic cells. The electron transfer system in cells and oxidation of glucose in the human body are example of redox reaction.
                      The term redox comes from two concepts involved with electron transfer, reduction and oxidation. It can be explained in simple terms.

  • Oxidation is a process of addition of oxygen  ( or ) removal of hydrogen ( or ) loss of electron ( or ) increase in oxidation state by a molecule, atom or ion.
  • Reduction is a process of removal of oxygen ( or ) addition of hydrogen ( or ) Gain of electrons ( or ) decrease in oxidation state by a molecule, atom or ion.                                 
Example of Oxidation-Reduction Reaction : ( Ionic Equation )
               The reaction between copper and silver in which copper is oxidized and silver is reduced. The ionic equation for this reaction is,

                              Cu (s) +2 Ag + →Cu2+ (aq)  +  2Ag (s)
The over all reaction may be written as two half-reactions.

Oxidation Reaction :
                              Cu (s) →Cu2+ + 2e-
    The above half reaction mention the solid copper is oxidized ( losing electron ) to form a copper ion with plus 2 charge.

Reduction Reaction :
                                   2Ag+(aq)  +  2e-  →  2Ag (s) 
Here, two silver ions are reduced to form a solid silver.
When adding the reactions together the electrons are canceled.
      Cu (s)  →  Cu2+ + 2e-

     2Ag+(aq)  +  2e-  →  2Ag (s
Cu (s) +2 Ag + →Cu2+ (aq)  +  2Ag (s)  

Note :
Copper metal is immersed in a solution of silver nitrate. The solution gradually acquires the blue color characteristic of the hydrated Cu2+ while the copper becomes coated with glittering silver crystals.

(The above figure is galvanic cell reaction. Its also referred as voltaic cell or Daniel cell.)

One more example for redox reaction :
    The reaction between hydrogen and fluorine in which hydrogen is being oxidised and fluorine is being reduced.
                                     H2 + F2  →  2HF

The over all reaction may be wrotten as two half reactions 
           H2    →   2H+  +  2e- ( oxidation )

           F2 + 2e-     →   2F-   ( Reduction )
Adding the reactions together the electrons are canceled.
                            H2    →   2H+  +  2e- ( oxidation )
                    F2 + 2e-     →   2F-   ( Reduction )
                      H2  +  F2  →   2H+  +  2F-

Ions combine to form a hydrogen fluoride. 
                        2H+  +  2F-    → 2HF
The overall reaction is,

               H2 + F2  →  2HF