PROCESSES OF REFINING

Refining: the process of purifying impure metals is called refining.

(A)        Liquation process: the process is based upon the difference in fusability of the metal and the impurities.when the impurities are less fusible the the metal itself, this process is used.the impure metal such as Bi, Sn, Hg, Pb,etc. is placed on the sloping hearth of the furnace and gentely heated. The metal melts and flows down.

(B)         Distillation: the process is used for those metals which are easily volatile. The impure metals are heated and the vapours are seperately condensed in a receiver. This is used for purification of Zn, Cd, Hg, etc.

(C)         Coupellation: the impure metal is heated in the couple or voal shaped crucible made of base ash or cement and removed with the blast of air. Impurityof lead in silveris removed by this process.

(D)        Poling : it is used for the purification of those metals which contains their own oxide as impurity. The molten impure metal is stirred with green poles of wood.

(E)          Electrorefining : metals like Cu, Hg, Au, Ni, Cr, Al, etc.are purified by this method.the impure metal is made as anode and a strip of pure metals is made is cathode while electrolyte solution consists of a solution of a suitable salt of metal.

(F)          Zone refining: when highly pure metals are required, this method is applied for purification. This method is based on the difference in the solubility of impuritiesin the molten or solid state of metal. This method is used in the purification of germanium gallium silicon etc. which are used as semiconductor.

(G)        Van arkel process : this method is used for the purfiaction of ultra pure metals. The impure metal is converted into a volatile compound which is then decomposed electrically to getpure metals. Ti, Zr, Hf, Si, etc are refined by this method.

(H)        Mond process: nickel is purified by this method. The impur nickel is treated with CO at 330-350K. when volatile nickel carbonyl is formed.the carbonyl is subjected to 450-470K when it is decomposes giving pure nickel.

(I)             Chromatographic method: it is based on the selective distribution of various contituents of a mixturebetween two phases, a stationary phase and a moving phase. The stationary phase either be solid or lightly bound liquid on the solid support. The moving phse may be a liquid or a gas. Different types of chromatographic mathods have been developed.

(J)            Leaching: leaching involves the treatment of the ore with is suitable reagent to make it soluble while impurities remain insoluble. The ore or the metal is recovered from solution by a suitable chemical method.

e.g natives ore of Ag and Au are treated with aqueous solution of nacn in the presence of oxygen. The Au and Ag particles get dissolved forming complex cyanides. Ag or Au is recovered from solution by addtion of electropositive metal Zn.

SOLUTIONS (CHEMISTRY)

                                           SOLUTIONS

Dissolution   When a solid solute is added to the solvent, some solute dissloves and its concentration increases in solution. This prosess is known as dissolution.

Saturated solution:  such a solution in which no more solute is dissloved at the same temperature and pressure is called a saturated solution.

Unsaturated solution: such solution in which more solute can be dissloved at the same temperature and pressure.

Factors affecting solubility

1.    Nature of substance

2.    Effect of temperature

3.    Effect of pressure

                      

                 SOLUBILITY OF A GAS IN A SOLUTION

Oxygen dissloves only to the small extent in water. It is this dissloved oxygen which sustains all aquatic life. On the other hand hydrogen chloride is highly soluble in water.the solubility of gases increases with increase in pressure.

Henry was the first to give a quantative relationship between pressure and solubility of gases in the solvent which is known as henry law.

The law states that at a constant temperature the solubility of the gas in the liquid is directly proportional to the pressure of the gas.

Dalton, a contemporary of henry, also concluded independently that the solubility of gas in the liquid is the function of partial prussure of the gas.

The most commonly used  form of henry law states that “the partial preussure of the gas in the vapour phase (p) is directly proportional to the mole fraction of the gas in the solution.

                   P     =K_hX

The solubility of gases increases with decrease in temperature. It is due to this reson the aquatic species sre more comfortable in cold waters rather  than in warm water.

Henry’s law find several application in industry and explain some biological phenolmena:

To increase the solubility of co2 in soft drinks and soda water , the bottle is sealed under high pressure.

Scuba divers must cope with high concentraction of dissolved gases while breathing air at high pressure under water.increased pressure increases the solubility of atmospheric gases in blood. When the diver cames towards surface, the pressure gradually decreases. This releases the dissolved gases and leads to the formation of bubbles of nitrogen in the blood. This blocks capillaries and creates a medical condition known as bend which are painful and dangerous to life. To avoid bend , as well as the toxic effect of high concentrations of nitrogen in the blood , the tanks used by scuba divers are filled with air diluted with helium.

At high altitude the partial pressure of oxygen is less than that of the ground level.this leads to low concentration of oxygen in the blood and tissues of people living living at high altitude or climbers.

Low blood oxygen causes climbers to became weak and unable to think clearly, symptoms of of a condition known as anoxia.

WAVE OPTICS

1.  1. Diffraction Pattern

The non-uniform distribution of light energy obtained on the screen due to bending of lights rays at the corners or edges of the slit is called diffraction pattern.

2. Diffraction

The bending of light rays around the edges and corners of the obstacles is called diffraction.

3. Width of central maximum:- The width of central maximum is the linear distance between the first minima on the either side of central maxima of the diffraction pattern.

4. Fresnel’s distance the distance of screen from the slit at which the spreading of light becomes just equal to the size of the slit is called Fresnel’s distance.

                                                D_f=a²/lemda

There are two classes of diffraction

1.  Fresnel diffraction

2.  Fraunhofer diffraction

the diffraction pattern is due to a single rectangular slit consists of broad and intense central maximum and a number of narrower and fainter maxi-ma called secondary maxi-ma on the sides of central maxi ma. The width of central maximum is twice the width of fainter side maxi-ma.

5. An arrangement consisting of a large no. of equidistant narrow parallel rectangular slits of equal width separated by equal opaque portions called a diffraction grating.

6. The ratio of the change in angle of diffraction of any two neighboring spectral lines to their change in wavelength is called dispersive power.

7. Prism diffraction is due to refraction. Grating spectra is due to diffraction. Prism spectra has only one order and hence brighter. Grating spectra has different orders and so light is distributed to different orders.

8. Polarization tells us about the transverse nature of light waves.

9. The phenomenon in which light vibrations are confined to a single plane is called polarization of light.

10. Plane polarized light can be produced by reflection, refraction, and scattering.

11. Brewster’s law: the tangent of the angle of polarization for a given medium is numerically equal to the refractive index of medium. The angle at which the refracted ray from a transparent medium is plane polarized is called polarizing medium.

12. Pile of plates is used to produce polarized light by refraction.

13. Malus law: Malus law stated that when a completely plane polarized light is incident on a polarizing sheet the intensity of light transmitted through the analyzer varies as the square of cosine of the angle between the plane of transmission of the analyzer and the plane of polarizer.

14. When a light rays is passed through calcite or quartz crystal we get two defracted rays .one refracted rays obeys the laws of reflection and is called the ordinary ray or O-ray. The other ray does not obey the laws of refraction and is called the extraordinary ray or E-ray.

15. When a beam of unpolarised light is passed through certain       crystal like tourmaline , the light splits up into two beams,  polarized at right angles to each other; the light with vibrations perpendicular to optic axis are absorbed and the other components with vibrations parallel to the optic axis is transmitted. The selective absorption is called dichroism and the crystal are said to be diachronic.

16. Polaroid work on the principal of dichroism.

17. Polaroid are made by embedding the tiny synthetic crystals of harapathitewith their optical axis parallel in the transparent film of cellulose acetate.

18. Polaroid are used, in motor car head lights , in sunglasses, to view 3d pictures, as filters in photographic camera.

ATOMS

ATOMS

The conclusion drawn from the alpha particle scattering experiments are

The positive charge of the atom is concentrated in a small core called the nucleus.

The whole mass of the atom remains in a small region of atom and the space around the nucleus is almost empty.

The shortest distance between the alpha particle and nucleus, when the kinetic energy of alpha particles becomes equal to the potential energy of alpha particle-nucleus system, is called the distance of closest approach of alpha particle during a head on collision.

Drawback of Rutherford atom model are, he could not explain the stability of atoms and origin of line spectrum.

According to Bohr, the angular momentum of the electrons is an integral multiple of h/2π. An electron does not radiate energy when it is in stationary orbit. Electrons radiate energy when the electron jumped from permitted high energy orbit to the lower energy orbit.

The difference between the energies between two states is radiated as a photon of energy hv.

The innermost orbit with n=1 is called the ground state. Other energy levels with n=1,2,3,… are called exited states.

The spectrum of light emitted by sun is called this solar spectrum and is found to be crossed by a large no. of dark and fine lines.

The energy required to raise an atom from its normal state to the exited state is called the excitation potential of the atom.

The ionization potential of an atom is the energy required to remove an electron from the ground state to an infinite distance from the nucleus.

The various quantum numbers needed to specify the state of an atom are 1.  The principal quantum number  2.the orbital quantum no. 3. Magnetic orbital quantum number  4.spin quantum no.

Pauli’s exclusion principle states that “no two electrons in an isolated atom can have the same values for all quantum numbers”.

X- Rays are electromagnetic waves having wavelength from 0.5 A 15A. X-Rays of long wavelength are called soft x-rays and that of short wavelength are called hard x-rays.

x-rays are produced when fast moving electrons are suddenly stopped by a target.

The intensity of x rays depend on the number of electrons further depend on the filament current.

The quality of x rays depend upon its penetrating power depend on the p.d. across the tube.

X rays are electromagnetic waves. They are not deflected in electric or magnetic field. The affect photographic plate. They can penetrate matter.

Moseley’s law states that the frequency of the spectral line in a x ray spectrum varies as the square of atomic number of the elements emitting it.

ADSORPTION(CHEMISTRY)

Absorption : It is a phenomena in which a substance is uniformly distributed all over the surface.

Adsorption : the existence of a substance at a surface in different concentration than in the adjoining bulk is called adsorption. It is a selective adsorption.

Types of adsorption: Depending upon the nature of forces between the molecules of adsorbate and the adsorbent, the adsorption may be classified as:

1.   Physisorption

2.   Chemisorption

Freundlich adsorption isotherm: the adsorption of a gas on the surface of solid depends upon the pressure of gas. The extent of adsorption is generally expressed as x/m, where m is the mass of adsorbent and x is the mass of adsorbate when equilibrium has been attained. On the basis of experimental studies, Freundlich established the following relationship between the amount of gas adsorbed (x) per unit mass of adsorbate (m) and the pressure (p).

                                      x/m =kp^1/n

Where n is a constant
(whole number)which depends upon the nature of adsorbate and adsorbent.

Factor affecting the adsoption of gases on solids :

1.   Nature of gas : the easily liquefiable gases like NH₃, HCL, CO₂, etc. are adsorbed to the great extent then the permanent gases such as H₂, O₂, N₂< etc.

2.   Nature of adsorbent : activated charcoal is the most common  adsorbent for the gases. The gases such as H₂, O₂, N₂, are adsorbed on the metal Ni, Pd, etc.

3.