Hack tech fact

 Order of complex reactions    The order of a complex reaction, i.e., a multi step reaction is determined by taking its slowest step known as rate determining step.         For example, in the reaction  2NO² + F² --> 2NO²F, the number of molecules involved is three, but the rate of the reaction determined experimentally is [NO²][F²]. Thus it's order is 2.                     Thus possible mechanism for the reaction, may be written as  NO² + F² --> NO²F + F ( Slow)  NO²F + F --> NO²F²     (Fast)  Example:  Reaction between NO and H² 2NO + H² -slow-> N² + H²O² H²O² + H² -fast-> 2H²O  

 Fraction order reaction The reaction whose order is a fraction is called a fractional  order reaction.  Example:       (1) - Thermal decomposition of acetaldehyde                   ∆ CH³CHO ---> CH⁴ +CO, rate = k[CH³CHO]¹.⁵ (2)- Reaction between H² and Br² to form HBr  H²(g) + Br²(g) --> 2HBr, rate = k[H²] [Br²]¹/²

Third order reaction:  In this reaction, the rate of the reaction depends upon the concentration of three reacting species. Example:  (1) Reaction between nitric oxide and oxygen 2NO +O --> 2NO²; rate k[NO]²[O²]  (2) Reaction between nitric oxide and bromine   2NO + Br² --> 2NOBr; rate = k[NO]²[Br²]

Second order reaction:  In this reaction, the rate of the reaction depends upon the concentration of two reacting species.  Example:  (1) Decomposition of nitrogen peroxide  2NO² --> 2NO + O², rate = K [NO²]² (2) Reaction between H²(g) and I²(g) to from HI(g) H²(g) + I²(g) 2HI(g), rate =  k[H²] [I²]  (3) Alkali hydrolysis of ester  CH³COOC²H⁵ + NaOH--> CH³COONa + C²H⁵OH, rate = k[CH³COOC²H⁵] [NaOH].

First order reaction: The reaction in which the rate of the reaction depends on the concentration of one reacting species is called a first order reaction.  Example: (1) Decomposition of nitrogen pentoxide in CCl⁴ solution                                      1 N²O⁵ -CCl⁴-> 2NO² + --- O², rate = k[N²O⁵] (2) Decomposition of ammonia nitrite in aqueous solution NH⁴NO² ---> N² + 2H²O, rate = k[NH⁴NO²] (3) Decomposition of hydrogen peroxide in the presence of pt catalyst                                 1 H²O² -Pt-> H²O + ---   O², rate = k[H²O²]  (4) Hydrolysis of methyl acetate in aqueous solution  CH²COOCH³ + H²O --H+--> CH3OOH + CH³OH  (5) Inversion of Cane sugar  C¹²H²²O¹¹ + H²O --H+--> C⁶H¹²O⁶+H²O Note: In the example 4 and 5, the concentration of H²O does not change as it's concentration is very high, i.e, 55.5mm                     

Order of a reaction:   Order of a reaction may be defined as - the sum of the power (coefficient) of the concentration terms of the reactants occurring in the rate determining step of a chemical reaction. Consider the following general reaction.                         aA + bB ---> products                        Rate = k [A]a × [B]b  Order of the reaction = a + b           The order of a reaction can only be determined from experiment. Thus, order of reaction is defined as the sum of powers raised on concentration terms in order to write rate expression from experimental evidences. 

Zero order reaction: The reaction in which the rate of the reaction is independent of the concentration of the reacting species is called a zero order reaction. Most of these reactions are heterogeneous in nature and take place on the surface of the crystalyst. Example:  (1)  photo chemical reaction between hydrogen and chlorine. H²(g)+Cl²(g)--hv-->2HCl(g), rate = K[H²]°[Cl²]° (2) Thermal decomposition of Hl on the surface of gold as catalyst                  ∆ 2NH³(g) -----> H²(g) +I²(g), rate                  Au = k[HI]° (3) Thermal decomposition of NH³ on the surface of pt catalyst at high pressure.                  ∆ 2NH³(g) -----> N²(g), rate = k[NH³]°                  Pt

Secondary cells : These are also called as storage cells or accumulators. In these cells the chemicals can be brought back to their initial state by charging the exhausted cell with electric current from an external source. Thus, the secondary cells can be used again and again by changing them. The electrical energy can be stored in these cells and these cells are called storage cells accumulators. The lead storage battery (or Acid storage cell) nickel - cadmium storage cells, and alkali storage cell (or, the Edison accumulator) are the secondary cells.

Primary cells:  In these cells, the chemicals used up during the supply of electrical energy cannot be regenerated by passing current into the used up cell from external source. In other words, the cell reaction is not reversible. It is, therefore, after sometimes, the battery becomes dead. Such primary cells are called dry cells. The dry cells are used in torches, radio receivers, electronic calculators, hearing aids, etc.

 Measurement of electrode potential:    The absolute electrode potential of an electrode can not be measured due to the following reasons :  (1) No half cell either oxidation or reduction can take place independently and can work only when both are connected. (2) The electrone releasing or accepting tendency of an electrode is only relative tendency and not absolute tendency.     Therefore, in order to measure the standard electrode potential of a half call, a reference electrode is required and an arbitrary electrode potential is assigned to it. The commonly used reference electrode is standard hydrogen electrode (SHE) also called normal hydrogen electrode (NHE) and it's standard electrode potential (oxidation or reduction) is taken as zero.

 Concentration of ions in the solution :  In the case of zinc in contact with Zn²+ ions in solution, Zn(s) <=> Zn²+(aq) + 2e an increase zinc ion concentration (i.e, oxidation) will tend to shift the equilibrium to the left. I.e., will decrease the electrode potential. Similarly, a decrease in zinc ion concentration (reduction) will decrease in zinc ion concentration (reduction) will increase the electrode potential. In other  words, the reduction potential of an electrode (E red) is proportional to the concentration of ions, and the oxidation potential of an electrode (E ox) is inversely proportional to the concentration of ions.

Single electrode potential:  In the preceding section, we knew that the potential of a single electrode in a half cell is called the single Electrode potential. In a Daniell cell in which the electrodes are not connected extremely, the anode, Zn(s)/Zn²+(aq). Cu²+(aq)/Cu(s) develops a nagative charge and develops a positive charge, respectively. The amount of charge produced on an individual electrode determines its single electrode potential.      It should be stated here that it is not possible to measure the single electrode potential experimentally. It can be determined in conjunction with a reference electrode thus constituting a complete electrochemical cell. Measuring the potential difference between the two electrodes of the complete cell and from the known potential value of the reference electrode, the potential of the required electrode can be determined.

Electrolytes :  These are the substances which conduct electricity in fused state or molten state or in aqueous solutions and undergo chemical decomposition. Their conduction are due to the presence of free ions. As solid state donot contain any free ions, thus, these substances are bad conductor of electricity in the state. The conductance of the electrolyte solution is called Electrolytic conductance or Electrolytic conduction.            Example : NaCl, HCl, H²SO⁴ etc.       An electrolyte in its fused state or in aqueous solution contains no detectable concentration of electrons. It conducts electricity not by virtue of the flow of electrons but as a result of the movement of ions which are electrically charged. Is why electrolytes are also called ionic conductors.

 Function of semi-permeable:  It may be recalled that when a solvent and a solution, or two solutions of different concentrations are separated by a semipermeable membrane (abbreviated as SPM), osmosis takes place resulting in the flow of solvent molecules from the solvent (or from a less concentrated solution) side to the solution (or to the more concentrated solution) side. Now the question is - How does the SPM work in osmosis?                    It is considered that the solvent (water) molecules get absorbed on on the surface of the SPM. The adsorbed layer on SPM leads to interaction between the solvent molecules on both side of the SPM. As a result, the solvent molecules can permeate through the SPM. Since the solute molecules don't get absorbed on the membrane, they cannot permeate.

 Effects of temperature:  In general, the solubility of a gas in a liquid decrease with increase of temperature. The process of solubility of gas in a liquid is exothermic in nature. It is because during the dissolution, a gas contract in volume and as a result, energy is released.                         F Gas + liquid  ---> Dissolved gas, ∆H _ ve                       <---                         B As per Le Chatelier's principal, the increase of temperature favours the reverse process and thus solubility of a gas decrease with rise of temperature.

 Nature of gas and solvent:  The solubility of gases in liquids depends both upon the nature of gas and the liquids (solvent).  (1) Generally gases which are easily liquefiable are more soluble in common solvents. For example, CO² is more soluble in water than H² and O².  (2) The solubility of a gas also depends upon the chemical nature of the solvents. For example, nitrogen and oxygen are much more soluble in ethyl alcohol than in water at the same temperature and pressure. It is because of the chemical similarity between the gas and the solvent. (3) The gases which are capable of forming ions in aqueous solution are much more soluble in water than in other solvents. For example, gases like HCL and NH³ are highly soluble in water but not in organic solvents in which they do not ionise.

 Colligative properties of dilute solutions :    In the preceding section, we described physical properties of pure liquids. In a binary solution behaving ideally, it was considered that the vapour pressure of the solution is the sum of the crystal partial pressure of the components constituting the solution. But, when a non-volatile solute, (e.g., sugar) is added to a volatile solvent, it is found that the vapour pressure of the solvent is lowered. In other words, the addition of a non-volatile solute to a volatile solvent alters or modifies the properties of the solution. In such cases the properties of the solution depends on the number of solute particles ( atoms, molecules or ions) and not on the nature of the solute particles. Now, we use the term colligative to  describe those properties of a solution which may be determined by taking simple arithmetic averages of the properties of solute and solvent.         The colligative properties of solutions are those properties which dep

 Why ferromagnetic substances make better permanent magnets? Ans- This is because the metal ions in a ferromagnetic substances are grouped into small regions called domains and each domain acts at a tiny magnet. These domans are randomly oriented, but when a ferromagnetic substances is placed in a magnetic field all the domains get oriented in the duration of the magnetic field which produces a strong magnetic field. This permanent magnetism persists even when the external magnetic field is removed. Therefore, ferromagnetic substances make better permanent magnet.

 Application of n -type and p - type semiconductors : n-type and p-type semiconductors have wide applications in the field of electronics. Some of its applications are described below.  1- A diode is a combination of n-type and p-type semiconductors which is used used as a rectifier. 2- The solar cell is an efficient photo-diode used for transformation of light energy into the electric energy.  3- n-type and p-type semiconductors are used detect radio or audio signal. 4- Due to fast response of Galinium arsenide it is widely used in semiconductor device.

 Thermal conductivity :  Metals are good conductor of heat. This is due to transfer of heat energy from one end to other by the free electrons. Tensile strength : Metals have high tensile strength, i.e. they can be stretched without breaking. This is due to the relatively strong electrostatic forces of attraction between the +ve Kernels and mobile valence electrons.

Anti-ferroelectricity: When the alternate dipole are aligned in opposite direction, the net dipole moment becomes zero and in such cases the crystal is called anti- ferroelectric and the phenomena is called anti-ferroelectricity. Examples of such solids lead zirconate  (PbZrO³)

Malleable and ductile: Metals are malleable and Ductile. The metals can be easily drawn into wires and can be twisted. This is due to the non-directional nature of metallic bond. When a deformation force is applied, the kernels of metals can slip over each other. Thus the crystal lattice gets deformed by the slippage of adjacent layers.

Hardness of metals: The metals are generally hard. The hardness of metals is due to strong metallic bond present in them. More is the strength of metallic bond, harder is the metal. The strength of metallic bond depends upon the number of valence electrons and size of kernel. More is the number of valence electrons for delocalisation, stronger is the metallic bond. Similarly, smaller is the size of +ve Kernels, greater is the force of attraction for delocalised electrons and stronger is the bond. For examples, alkali metals due to the presence of only one electron in their valey shell and larger size of atom form weak metallic bond and thus are soft metals.

Electrical conductivity of metal : Metals are good conductor of electricity which is due to the presence of mobile electrons in the crystal lattice of the metals. It has been found that the increase of temperature decreases the electrical conductivity of metals. This is because increase of temperature increases the Kinetic energy of the metal atoms which start vibrating the Kernels of metal vigorously. This interacts with the movement of electrons and make its movement slow and thus conductivity decreases.

 Application of super conductors :   1- In the field of electronics as super conducting cables, electronic devices. 2- In power transmission sector and in levitation transportation, i.e., trains which move in air without rail. 3- In cryogenic gyro operated instruments. 4- In lazer technology and computers. 5- In building supermagnets. 

Piezoelectricity : The crystals in which the dipoles align themselves in the same direction leading to resultant dipoles when certain external mechanical stress or pressure is applied on it are called piezoelectric and this phenomenon is called piezoelectricity. When some pressure (stress) is applied on such crystals there is displacement of ions in the crystal which result in the formation of electric current. Therefore, such crystals are used as mechanical electrical transducers. For example, such crystals are used as pickups in record players as they produce electric signals when pressure is applied on them. Piezoelectric crystals are also used in microphones, ultrasonic generation, sonar detectors etc.        The reverse effect may also produce in these crystal when placed in an external electric field leading to the deformation .

Ferroelectricity: The dipoles in certain solids are spontaneously aligned, in a particular direction, even in the absence of electric field. Such substances are called ferroelectric substance and the phenomenon is called ferroelectricity. However, the direction of polarisation in these substances can be changed on applying electricity. Examples of ferroelectric solids are (BaTiO³), Rochelle salt (sodium potassium tartarate), potassium dihydrogen phosphate) (KH²PO⁴) etc.

Paramagnetic substances:   The substances which are weakly attracted by magnatic lines of force are called paramagnetic substances and this phenomenon is called paramagnetism. These substances possesses permanent magnetic dipoles due to the presence of unpaired electrons. These substances lose their magnetic behaviour in the absence of an external magnetic field i.e. their magnetic behaviour is temporary. Examples, many transition metals and their ions i.e. TiO², VO², CuO, FeSO⁴ etc.

Ferromagnetic substances :  These are the substance which are strongly attracted by the magnetic field and exhibit permanent magnatic behaviour even when magnetic field is removed. Examples, Fe,Co,Ni,CrO².      The properties of ferromagnetism arises due to the alignment (orientations) of magnatic moment in the direction of the external magnetic field and as a result a strong magnetic field is produced and the substance behaves like a permanent magnet. For example, CrO² is used to make magnetic tapes in audio and video recorders.

Frenkel defect: This defect was discovered by russian scientist Frenkel in 1926 in ionic crystals. This defect arises when certain ion found missing from its normal sites and occupy positions elsewhere in the interstitial sites in the crystal lattice. In this case, the crystal remain electrically neutral as the number of cation and anions remain same. This defect is shown below where a cation A+ is found missing from its normal site and present in one of the interstitial sites in the crystal lattice.

About Schottky defect:   This defect arises in the ionic and was discovered by German scientist Shottky in 1930. This defect arises when equal number of +ve and -ve ions are found missing from their normal lattice sites. Taking example of an ideal crystal A+B- the arrangement of ions in an ideal crystal and Schottky defect crystal are shown below   An ideal crystal Schottky defect in crystal In case of (I) Strongly ionic compounds having high co-ordination number and (ii) Cation the anions having almost equal sizes.

 Packing of particles in crystal: In a crystal the constituent particles are closely packed. If maximum available space is occupied by the constituent particles, a crystal is said to be closely packed and have maximum density and stability. The close packing, however depends on the shape and size of the constituent particles in close packing. Assuming the constituent particles to be hard spheres of equal size.

 Bragg's model of X ray diffraction : According to Bragg's, a crystal which is made up of series of equally spaced atomic planes, can be treated as a transmission grating and a reflection grating as well. When X-rays are incident on a crystal face, some of the rays will pass undeflected and some other rays will penetrate into the crystal and strick the atoms in successive planes. From each of these plans the X-rays are reflected (i.e., X-rays strick with electrons in the atoms of the structural units and undergo a change in direction), in all directions. For the formation of an intense diffraction pattern in any direction the condition is that the angle of incidence should be equal the angle of reflection of the beam for the direction studied.               Bragg's equation can be applied either to the reflection or the diffraction experiment. In the case of reflection from the crystal surface, the angle ∅ stands for the angle between the crystal surface and the duration of

Nature of diffraction patterns : The big spot in the centre of the pattern corresponds to the unscattered beam. The other spots represent the scattered beam through different characteristics angles. The spreading of X-rays from each lines of atoms in the crystal gives rise to region of various intensities. Diffraction patterns depends on the symmetry of the crystals, and helps in determining the crystal structure.

Structure of simple ionic crystals:   In ionic crystals lattice positions are occupied by positive and nagatives ions in equivalent amounts. In such crystals positive ions are surrounded by negative ions and vice-versa. Since the coulombic forces holding the oppositely charged ions together in an ionic crystal are non directional, the arrangement of ions in the crystal is largely controlled by the sizes and charges of the ions concerned. Normally, each ion is surrounded by the largest number of oppositely charged ions. The number of oppositely charged ions surrounding an ion is the co ordination number of the ion and is related to the relative sizes of the positive and nagative ions. We will discuss below the different types of ionic compounds, depending upon the relative number of positive and nagative ions present in them.

 Imperfections or Defects in crystalline solids : In an ionic crystal the particles are well orderly arranged in a regular pattern. An ideal crystal is that which has same until cell containing the same lattice points through out the whole crystal. But, such ideal crystal only exists at zero Kelvin temperature i.e., entropy of it's particle is zero. It means that there is no movement of the constituent particles at 0K. But, none of the crystals are basically ideal and it suffers certain defect at temperature above 0K. This defect may arise due to some irregularities in the arrangement of constituent particles in the crystal lattice and are called imperfections or crystal defects. These are of two types. Point defects:                 These defect are due the irregularities in the arrangement of atoms around a point or an atom in a crystalline solid. These are also called atomic defects. Line defects:                   These defects are due to the irregularities in the arrangement o

Rutile structure: The radius radio is in the range 0.73 to 0.41. in rutile (TiO²) each Ti⁴+ ion is octahedrally surrounded by six O²- ions whereas each other O²- ion is surrounded by only three Ti⁴+ ions arranged at the tree corners of a plane triangle. The Co-ordination number of Ti⁴+ and O²+ ions are 6 and 3, respectively. It is not exactly a close packed structure. Ti⁴+ ions in rutile may however, be considered as forming a sufficiently distorted body centred cubic lattice.           Example  compounds  having radius ratio below 0.41 are SiO² and BeF² but these are only a few. The Co-ordination number of Si⁴+ and Be²+ is four and that of O²- is two. However, these are appreciably co-valent.

 Fluorite structure :  In CaF², the radius radio is 0.732 which gives rise to a body - centred cubic (bcc) structure. In this case each Ca²+ ion is surrounded by eight F- ions, so the co-ordination number of Ca²+ is 8. Since in an ionic compound containing different numbers of cation and anions, the cation and anion have different co-ordination numbers, it follows that the co ordination number of F- ion is four (since the number of F- ions is double the number of Ca²+ions). Thus, CaF² has 8 : 4 arrangements. In fluorite, Ca²+ ions are too small to touch each other hence, the structure is not strictly close packed structure. 

 Results of Schottky defects:  Because of missing of ions, the ionic compounds show following changes in the properties of ionic crystals.  1- The density of the crystal decreases. 2- The stability and lattice energy of crystal decreases. 3- The electrical conductivity of the crystal increases. It is because when electricity is applied, the ions move to the vacant place and this process continues in the whole crystal lattice resulting in the increase of electrical conductivity of crystals. Alkali metal halides such NaCl,KCl,KBr, CsCl etc. Normally show this defect.

Results of Frenkel defect:    1- It increase the electrical conductivity of the crystal because of the presence of vacancy in crystal lattice.  2- It decrease the stability or lattice energy of the crystal. 3- This defect does not change the density of crystal because the number of ions per unit volume remain same in the crystal. 4- It increase the dielectric constant of the crystalline solid as the similarly changed ions come closer. This defects are generally found in (i) AgCl,AgBr,Agl etc. It is because Ag+ ion being small in size occupy the interstitial sites leaving its own position in crystal lattice (ii) Further this defect is also noticed in ZnS crystal because of small size of Zn²+ ion which can fit in its own interstitial sites. (iii) Alkali metal halides don't exhibit this defect because of large size of alkali metal ions.

Position of nobel gases in the periodic table: The inert gases were not discovered at the time when Mendeleef gave his periodic table. He also could not imagine the presence of such elements devoid of chemical reactivity and thus left no place for these elements in his periodic table. As these elements are chemically inert, they should be placed in between the highly electronegativity halogens (VIIA) and highly electropositive alkali metals (IA), I.e., in the zero group. Further, it has been found that all these elements have fully filled stable electronic configuration, i.e., they have no tendency either to lose, gain or share electrons with the atoms of other elements. In other words, their valency is zero. Therefore, they have assigned zero group in the periodic table. Zero group is also numbered as group 18  in the modern periodic table. Basing upon their electronic configuration, it has been found that expect helium all other inert gases have eight electrons in their valence shell

 Schottky defect  1- It is found in case of ionic crystals. 2- The electrical conductivity of the crystal increases. 3- The stability of the crystal decrease. 4- Equal number of cation and anions are missing from their normal lattice sites. 5- It decrease the density of the crystal. 6- Dielectric constant value remain same. 7- It is observed in case of ionic compounds having high co-ordination number. 8- these are noticed in case of ionic compounds where cation and anions are almost of equal sizes. 9- These are observed in case of alkali metal halides.

 Application of Henry's law: (I) In the soft drinks, e.g., soda water, beer, in order to increase the concentration of CO² the bottles are normally sealed under high pressure of CO² High pressure of CO² inside the bottle increases the solubility of CO² as per Henry's law. When the bottle is opened, the pressure on the surface of the liquid decreases and as a result, CO² comes out of the bottle along with liquids of drinks. (II) Deep sea divers used compressed air for oxygen. According to Henry's law, the nitrogen of air dissolves in the blood of sea divers due to high pressure when the diver is in the deep sea. When the diver comes to the surface, the pressure decreases and the nitrogen dissolved in the blood escape out thereby  causing a painful sensation called cassion sickness or bent. In order to avoid this sort of difficulties, He and O² mixture is taken in place of air which is less soluble in blood. (III) Henry's law explains the function of lungs. When air enter

Frenkel defect : (I) It is also found in case of ionic crystals.  (II) The electrical conductivity of crystal increases. (III) The stability of the crystal decreases.  (IV) Ions leave their normal position and occupy some where else in the interstitial sites in crystal lattice.  (V) The density of crystal remain same. (VI) Dielectric constant value increases. (VII) It is observed in case of compounds having low co-ordination number. (VIII) These are noticed in case of ionic compounds where cation are smaller in size than anion. (IX) These are observed in case of silver halides.

Solubility of liquid in liquid: The solubility of two different liquids depends upon the nature of force of attraction among them. For example, (I) Ethyl alcohol is soluble in water due to intermolecular H-bonding among them. (ii) Benzene and carbon tetrachloride are soluble because of van der Waals force of attraction among them.  

 Azeotropes (constant boiling liquid mixtures) : The solution which show positive deviation from Raoult's law, at one of the intermediate compositions have total high vapour pressure or low boiling point. On the otherhand, the solutions showing negative deviations from Raoult's law, for one instermediate compositions, shows lowest vapour pressure highest boiling point. For liquid pairs of such intermediate compositions, the compositions of both liquid and vapour phases is the sane. As a result, both the components present in the liquid mixture will boil at the same temperature without undergoing any change in composition.         This type of liquid mixture which boils at the same temperature without undergoing any change in composition is known as constant boiling mixture or azeotropic mixture or azeotroes.  Azeotropic liquid mixtures present in binary solution are of two type:  (I) Minimum boiling azeotropes:  These are formed in case binary liquid mixtures showing positive d

Maximum boiling azeotropes : These are formed in case of binary liquid mixtures showing negative deviations from Raoult's law. Such azeotropes have boiling point higher than either of its pure components for example, a mixture containing 68% nitric acid (boiling point 3.73 K) form a constant boiling azeotropes having boiling point. 393.5K.   

Minimum boiling azeotropes: These are formed in case binary liquid mixtures showing positive deviation form Raoult's law. For example, a liquid mixture 95.57 mass percent of ethyl alcohol and 4.43 mass percent of water represents a constant boiling azeotropes. This mixture boils at 351.1K which is less than the boiling point of both ethyl alcohol (351.3 K) and water (373 k). This is known as minimum boiling azeotrope because the partial vapour pressure of both the components are maximum. At it's boiling point, both water and ethyl alcohol distill over as if they are the constituents of pure liquid.

Membrane bombardment theory: According to this theory, Osmosis arises due to unequal bombardment of solvent molecules  on both sides of a semipermeable membrane. Since, the surface covered by solvent molecules is more in solvent side than in solution side, there are lesser bombardment per unit area of the surface on the solution side than on the solvent side. Hence, due to the unequal bombardment, the solvent molecules on the solvent side will diffuse more faster through the membrane than on the solution.

The Adsorption theory: According to this theory a membrane is permeable to the molecules which get absorbed on it. For example, water molecules (solvent) are absorbed on the surface of a membrane due to polar interactions and maintain a connection between the water molecules of both solvent side and solution side. As a result, the solvent molecules pass easily through the membrane while solute molecules can not.

Solution theory :  According to this theory, the substance which dissolves a semipermeable membrane can pass through it. For example, phenol works as a semipermeable membrane between pure water and calcium nitrate. It allows water to pass through it because it is dissolved in water other hand, on the Ca(NO³)² molecules donot pass because it does not dissolved in phenol 

Vapour pressure theory: According to this theory pure solvent molecules can pass through the semipermeable membrane when it's pressure is higher than that of its solution.

Sieve theory:    In this theory semipermeable membrane is considered as a sieve consisting of large number of fine pores. These pores allow the molecules of solvent which are similar in size through them as compared to the size of solute molecules. But this theory fails explain the cases where solute molecules are smaller in size than solvent molecules.

Potential electrolytes (or ionogens) : These are incapable of conducting electricity in molten or liquid state. On dissolving, they form ions as a result of their interaction with solvent molecules. All acids, SnCl²,AlCl³, are examples of this type. These are also referred to as pseudo - electrolytes.

True electrolytes (or ionophores) :   These are ionic in pure liquid state and their melt conducts electricity, e.g., NaCl, NaNo³, K²SO⁴ etc. When dissolved, the solvent tear off the ions from it's lattice, solvates them and makes them mobile.  

Electrolytes - Electrolytes are classified as strong electrolytes and weak electrolytes on the basis of their relative conductance. Strong Electrolytes: These substances are high conducting in dissolved or molten state and possess ionic and polar or hydrogen bonded molecular crystalline structure. Halides, hydroxides, acetates of Group I A, and II A, element, nitrates, sulphates and chlorates of monovalent and divalent cations. HCl, HBr, Hl, H²SO⁴, HClO⁴, HNO³, . Are example of this type.

Oxidation potential  (Eox)  (1)- It is the tendency of an electrode to lose electrons. It is indicated as E m/mn+. (2)- It is the opposite value of reduction potential. Ex. Eox Of Cu is -0.34V  (3)- Oxidation potential of an electrode                        1                ___________                conc.of ions.

 Electrode potential (Emn+/m) : Cell potential (Ecell): Electrode potential- It is generally the reduction potential of the electrode when it is in contact with the solution containing ions of the electrode material  Cell potential- It is the difference of the reduction potentials of the two electrodes placed in contact with their respective electrolytic solutions in the two half cells i.e. E cell=  Ecathode -   Eanode

Ionic conductance: The conductance of an electrolytic solution depends upon the conductances of the ions forming the electrolyte. We know that the molar     (or. equivalent) conductance of an electrolyte solution increase with dilution and at infinite dilution it approaches a maximum limiting value. At infinite dilution, an electrolyte dissociates completely into ions and each ion contributes it's definite share to the total molar (or, equivalent) conductance of the electrolyte. In other words l, the molar (or, equivalent) conductance of an electrolyte solution is an additive property, I.e., the sum of the conductances of the ions (called the molar (or, equivalent) ionic conductances) in the solution.

Reduction potential (Ered)   1- It is a tendency of an electrode to gain electron. It is indicated as E mn+/M . 2- It is the opposite value of oxidation potential. Ex. Ered of Cu is + 0.34V. 3- Reduction potential of an electrode conc. Of ions.

 Electromotive force: 1- It is the difference between electrode potentials of two electrodes. 2- It is measured by a potentiometer. 3- EMF is the maximum voltage obtained from cell. 4- It is responsible for the flow of steady current.

Potential deference: 1- It is the actual difference in potential of the two electrodes when they are connected externally and current is flowing through the circuit . 2- It is measured by a voltameter. 3- It is less than EMF (It is because EMF) is the limiting potential difference at zero current with no consumption of energy. 4- It is not responsible for the flow of steady current.    

Chemical kinetics: The branch of physical chemistry which deals with the study of the rates of chemical reaction and with the description of the mechanism by which they proceed is called chemical kinetics.     The study of chemical kinetics involves (i) the study of the rate of  reaction and rate laws, (ii) the factors, such as temperature, pressure, concentration and catalyst that influence the of a reaction, and (iii) the mechanism in which a reaction takes place.

 Order of the reaction :   1- It is the sum of powers of the concentrations in the rate law expression. 2- It is an experimentally determined value obtained from the rate of overall reaction. 3- It may be a whole number, a fraction, or zero. 4- It cannot be obtained from a balanced chemical equation. 5- The mechanism of a chemical reaction cannot be known from the order of the reaction. 6- It can change with the conditions, such as pressure, temperature and concentration.

Molecularity of reaction: 1- It is the number of reacting species undergoing simultaneous collisions in the reaction. 2- It is a theoretical concept which depends upon the rate determining step in the reaction mechanism. 3- It is always a whole number and never zero, and generally never exceed three. 4- It is obtained from a single balanced equation. 5- The reaction mechanism can be know from the molecularity of a reaction. 6- It is invariant for a reaction.

 Adsorption: 1- It is a surface phenomenon. 2- The concentration of the adsorbing substance (adsorbates) is higher at the surface (of adsorbent) than in the bulk. 3- It may be +ve or -ve depending on the larger or less concentrations of the adsorbed substance on the surface of the adsorbent. * When the concentration of adsorbates is more on the surface of the adsorbent than in the bulk it is called positive adsorption, on the other hand, when the concentration of adsorbates is less on the surface of the adsorbent than in the bulk, it is called negative adsorption. 4- It is a rapid process. 5- The rate of adsorption is rapid initially but decrease slowly. Examples:  Water is adsorbed by silica gel. Ammonia is absorbed by charcoal.

Absorption: 1- It is an interior or bulk phenomenon. 2- The concentration of absorbed substance is uniform throughout the absorbing substance. 3- it is neither +ve or -ve, it is uniform. 4- It is a slow process because of diffusion. 5- The rate of absorption is uniform throughout. Example:   Water is absorbed by anhydrous calcium chloride. Ammonia is absorbed by water. 

Minerals:        The naturally occurring materials found in the earth crust in which metals are present in the native form or in combined state along with other impurities are called minerals or natural substances in which metal or their compounds are found in the earth's crust are called minerals.

Diffusion 1- It occurs directly and does not require any semi-permeable membrane. 2- Both the molecules of solute and Solvent move from a higher concentration to lower concentration. 3- It is applicable to both gases and liquids. 4- It can not be stopped by applying external pressure.

Osmosis 1- It takes in the presence of a semi-permeable membrane. 2- Solvent molecules move from a solution of lower concentration to that of higher concentration. 3- It is restricted to solutions only. 4- Osmosis ceases when an external pressure is applied.

 Electrolytic conduction: 1- Current passes by the movement of free ions. 2- Transfer of matter takes place in form of ions. 3- Change in Chemical properties takes place due to decomposition of electrolyte. 4- Resistance decreases or conductance increases due to increase in temperature. It is because due to increase in temperature, the viscosity of the medium and degree of hydration of ions increase which increase the movement of ions.

Metallic conductions 1- Current passes by movement of free electrons.  2- No transfer of matter takes place.  3- No change in chemical properties takes place  4- Resistance increase or conductance decreases due to increase in temperature. It is because due to increase of temperature thermal motion of metal ions increase which result in hindrance of flow of electrons.  

Electrolytic refining : Metals having large positive electrode potentials are purified by this method. The Metals to be purified should have lower discharge potential than the impurities. For example, during the purification of Cu metal, impure metal is made anode, a piece of pure metal is made cathode and electrolysis is carried in an electrolytic bath containing acidified CuSO⁴ as electrolyte.

 Van Arkel method: This method is called the vapour phase refining in which metal is converted to a volatile stable compound without affecting the impurities. The volatile compound is then decomposed to give pure metal. In this method ultrapure metals are obtained. Titanium and zirconium are refined by this method.

 Electrolytic refining: Metals having large positive electrode potential are purified by this method. The metals to be purified should have lower discharge potential than the impurities. For example, during the purification of Cu metal, impure metal is made anode, a piece of pure metal is made cathode and electrolysis is carried in an electrolytic bath containing acidified CuSO⁴ as electrolyte.

Electrolytic cell: 1- It is a device which convert electrical energy to chemical energ y. 2- In this cell +ve electrode is anode involving oxidation and -ve electrode is cathode involving reduction reaction. 3- In this cell electrons enter the cell from cathode to anode. 4- In this cell, electrodes are placed in the electrolytic solution in one containers. Chemical reaction is non spontaneous I.e. it takes place only by the passage of electricity.

Zone refining or Fractional crystallisation: Metals in high purity can be obtained in this method which is based on the difference in solubility in the liquid and solid states of the metal, and that of impurity, Ge,Si, and Ga used as semi-conductors are refined by this method. Gallium arsenide and indium antimonide used as semi-conductors are also refined by this method. In this method, a circular heater is fitted around a rod of impure metal and slowly moved over the rod. At the heated zone, the rod melts and as the heater moves, pure metals crystallises while the impurities drain away to the other part. The heater may have to be moved from one end to the other end of the rod more than once.  

 How we can separate two sulphide ores by froth flotation process? Explain with an example. Ans.            Two sulphide ores can be separated by adjusting the proportion of oil in water or by using depressants. For example, if an ore contain ZnS and PbS, a depressants NaCN is added so that it forms a complex with ZnS and prevents it from coming to the fort. On  the other hand, PbS comes into the forth and get separated.

 Zone refining or Crystallisation: Metals in high purity can be obtained in this method which is based on the differences in solubility in the liquid and solid states of the metal, and that of impurity, Ge,Si and Ga used as semi-conductors are refined by this method. Gallium arsenide and indium antimonide used as semi-conductors are also refined by this method. In this method, a circular heater is fitted around a rod of impure metal and slowly moved over the rod. At the heated zone, the rod metals and as the heater moves, pure metals crystallises while the impurities drain away to the other part. The heater may have to be moved from one end to the other end of the rod more than once.

Nature of metal and it's ion :  The electrode potential depends on the tendency of the electrode to form ions. It is a fact that no two electrodes have the same electron structure and therefore, no two electrodes have the same tendency to release electrons forming ions, I.e., the same electrode potential. For example, sodium being extremely active, loses electrons readily and has, therefore, high electrode potential. Cooper on the other hand being less active has a lower electrode potential.

Liquation:  Impure metals in the form of ingots (blocks) are placed in upper part of a slanting hearth maintained at a temperature slightly above the melting point of metals. The pure metals melts and drains away while the impurities remain behind as dross in the hearth.  

 Physical methods of refining : Distillation-                  Volatile metals containing non volatile impurities or vice versa are purified by this method. For example, low boiling points metals such as Zn and Hg are distilled by this method leaving behind less volatile impurities. Zn and Hg vapours are collected and condensed to get solid Zn or Hg.

 Heat treatment of steel: The properties of steel are modified on heat treatment: (1) Annealing:    In this process, steel is heated to a bright red heat and cooled slowly. By annealing, steel becomes soft. (2) Hardening:   when steel is heated to a bright red heat and cooled suddenly by dipping in oil or water (quenching) hard and brittle steel is obtained. (3) Tempering:   When steel is heated to a temperature much below redness and cooled slowly, the steel obtained is neither so hard or so brittle. (4) Nitriding:   In this case the steel is heated in an atmosphere of ammonia so that the surface is coated with hard iron nitride.

L . D PROCESS   to manufacturer best quality Steel: This is one of the most modern process of manufacturing best quality of steel and is used by Rourkela steel plant. The name L.D. stands for Lizard Donawitz, the names of places in Austria where it is first generated. This process makes use of L.D. converter which resembles like a Bessember converter in shape and has no holes at the bottom. It is fed with molten cast iron from the blast furnace and pure oxygen gas at high pressure is passed into it cooled by water at it's upper part. The impurities are oxidised and from which are removed. Then some alloy elements are added to molten mass to obtain steel of desired composition.

Electric arc process: In the process the the furnace consist of steel container lined inside with dolomite or magnesite provided with movable and water jacked electrodes fitted from the roof or from the sides of the container. A mixture of cast iron ore and scrap steel is taken in the container. On striking the electric are between the electrodes, heat is produced and the mixture melts. The impurities such as Si,mn,S and p combine with the basic lining and slaged off. The steel obtained is free from sulphur and gas bubbles. Alloy steels with high melting points are obtained in this process. High grade steel is obtained by this process. Steel so obtained is used for making utensils, swords, girders, etc.

 Different forms of iron: Mainly there are three commercial forms of iron. These are discussed below: 1- Cast iron or pig iron: It contains about 2 to 5% of carbon along with other impurities such as S,Si,p,Mn etc. It used as sewage pipes and plates as it is resistance to corrosion. 2- Wrought iron:  It is the purest form of iron containing 0.25% of carbon. It is malleable can be easily welded. 3- Steel:  It contains about 0.25 to 2 % of carbon i.e, the carbon content of steel is more than that of wrought iron and less than that of cast iron.

Zinc Refining:  - The zinc obtained by the process is impure and contain largely cadmium along with it. The impure is zinc is Known as spelter. Pure Zn obtained by Fractional distillation were Cd being more volatile (b.pt 775°C) than Zn (b.pt 906°C) distills over leaving behind pure Zn.              Zn can also be purified by electrolytic method. In this method impure Zn is made anode, pure Zn plate is made cathode and ZnSO⁴ solution containing little sulphuric acid is used as electrolyte. On passing electricity pure Zn is deposited at the cathode.

Extraction of copper Copper is extracted from the non-sulphide ores such as Malachite, azurite, etc. Following steps are involved in the extraction process using non-sulphide ores. 1- Cruising of the ore to a fine powder. 2- Concentration by Gravity process. The  3- calcination  4- Smelting  5- Leaching process

Leaching process:  Copper can be extracted from the concentrated oxide or carbonated ore by leaching process. This concentrated ote is treated with dilute sulphuric acid when copper sulphate is obtained in solution. From this solution, metallic copper is precipitated with iron fillings or recovered by electrolysis using lead anodes and pure copper cathode.

 Electrometallurgy:  The process of extraction of electro positive metals or highly reactive metals such as Na , K, Mg Al are not possible by pyrrometallurgical process. Therefore, these are extracted by electrometallurgical process.                The process of extraction of electropositive metals or highly reactive metals from their fused salt by electrolysis is called Electrometallurgy.

Metallic character: The elements of group 15 are less metallic than group 14 elements. However, metallic character increases on moving down the group.  Reason: Due to the increased nuclear charge and higher electronegativity, the elements of the group 15 are less metallic than the corresponding elements of  group 14. As on moving down the group, atomic size increases and electronegativity increases the valence electrons become loosely held and are lost more readily. Therefore, on moving down the group metallic character increases. In this family, N and P are non metals, As and Sb are metalloids While Bi is a typical metal.

Allotropic forms of phosphorus Phosphorus is found in many allotropic forms. But the important things of allotropic phosphorus are   White or yellow phosphorus ,R phosphorus ,Black phosphorus White or yellow phosphorus: This is the most common variety of phosphorus and is very reactive. Pure from is white and on exposure to light it turns yellow due to the Formation of a thin of red coating on it's surface   

 Thermal and Electrical conductivities:  Both thermal and electrical and electrical conductivities of theses elements increase on moving down the group. It is because the delocalization of electrons increases from the nitrogen with a co ordination number of six. Thus , N and P are non conductor while Bi is a good conductor of electricity.

 Allotropy of Group 15 elements : All the elements (except Bi) of this group show allotropy. Solid nitrogen exists in two allotropic forms, i.e., Alfa-nitrogen with cubic crystalline structure and Bita-nitrogen with hexagonal crystalline structure.  Phosphorus exists in a number of allotropic forms, such as white,red,scarlet, Alfa-black, Bita-black and violet. Arsenic exists in three allotropic form, i.e., grey, yellow and black. Antimony exists in three allotropic forms, i.e., yellow,black and explosive.

Uses of copper: Copper can be used a number of purposes. 1- For manufacturing electric articles,wires, etc . 2- For the manufacturing alloy and silver coins. 3- In the copper plating and electrotyping . 4- For covering the bottom of wooden ships. 5- For making utensils, calorimeters, and vacuum pans.

 Occurrence Nitrogen : Nitrogen was discovered by Daniel Rutherford in the year 1772. As it was found from nitra, it's name was given nitrogen. It exists in diatomic state and thus it is named as dinitrogen. Occurrence:                                    it occurs in the nature both in the free and combined state. Air contains 75% by weight and 80% by volume of nitrogen. In combined state it is mostly found as Chile salt pertre(NaNO³), Indian salt petre (KNO³)  ammonium salts, etc. It is found in the plants and animals as amino acids and proteins.

Ammonia- Ammonia is present in traces  in atmosphere. It is also found in soil where nitrogenous matter, such as urea decomposes to ammonia. This is also formed by the bacteria decomposition of nitrogenous matter of plants and animals. It is also found in Jupiter and Saturn in abundance.                       Ammonia is one of the most important compounds of nitrogen. It was first prepared by Priestly in the year 1774.

 Physical properties of dinitrogen: 1- It is a colorless , odour less, tasteless and non toxic gas.  2- It is partially soluble in water but it's solubility in water increases by the rise of pressure. 3- It is neither combustible nor a supporter of the combustion. 4- It has low boiling point (77.2k) and freezing point (63.2k). 5- It is adsorbed by activated charcoal.

Uses of Dinitrogen -  It is used-  1- For the manufacturer of the nitric acid, ammonia, nitrolim, etc. 2- To provide inert atmosphere in certain metallurgical operations. 3- For feeling electric bulbs. 4- Liquid nitrogen is used as refrigerant to preserve biological materials, food materials. 5- Nitrogen gas filled thermometers are used for measuring high temperature. 6- As cryogen in cryosurgery i.e., used in cooling a localized area of skin prior to remove wart or other unwanted or pathogenic tissues. 

Tests of ammonia: 1- It is detected by it's characteristics pungent odour. 2- It forms a dense white fumes of ammonium chloride with a drop of conc. HCL. 3- It gives a deep blue colour with CuSO⁴ solution. 4- It turns moist red litmus paper blue and moist turmeric paper brown. 5- It forms a reddish brown ppt with Nessler reagent.

Fuming  Nitric Acid When NO² gas is dissolved in conc. Nitric Acid, it forms fuming nitric acid. It is also obtained by distilling concerned nitric acid with a little starch. Nitric acid is reduced to No² by starch which dissolves in the remaining acid to from fuming nitric acid. This acid is yellow in colour due to the presence of NO² in it. It is a powerful oxidising agent and nitrating agent as compared to conc. HNO³.

 Uses of Nitric Acid It is used 1- In the manufacturer of fertilizers like calcium ammonium nitrate (CAN). 2- In the preparation of dyes , medicine , perfumes etc. 3- In the purification of silver and gold in the form of aquaregia.  4- For the manufacturer of explosive substance like TNT, nitroglycerin, picric acid, etc. 5- In the manufacturer of artificial silk. 6- As a laboratory reagent. 7- In the manufacturer of the sulphuric acid. 8- For the nitration of organic compounds.

A little about Group - 16 elements: The elements, oxygen (O), sulphur (S), selenium (Se), tellurium (Te) and polonium (Po)  constitute group 16 or VIA of the periodic table. These elements are commonly known as Chalcogens or ore forming elements because the ore of many metals occur as oxides and sulphides. As oxygen is the first member of this group, these are commonly known as oxygen family members.  

Siemens Ozoniser:  This Ozoniser consist of two co-axial glass tubes fused together at one end. The outer side of the outer glass tube and the inner side of the inner glass tube are finally coated with tin foils as shown in the figure given below.  (Siemens Ozoniser)->2                                                     (Siemens Ozoniser)->1 These tin foil are connected  to the induction coil for supply of silent electric discharge. Pure and dry oxygen gas is passed into the apparatus through annular space. The gas is then subjected to the action of silent electric discharge where oxygen gets converted into ozone. The ozonised oxygen then comes out  of the apparatus through the outlet of the Ozoniser. (Siemens Ozoniser)->2

 Laboratory methods of preparation - O zone is prepared by passing silent electric discharge through dry, pure and cold oxygen.     3O²  ---->   2O³, ∆H= + 68 Kcal.        <----  Since the formation of ozone is endothermic, it requires high energy which is obtained by silent electric discharge. The silent electric discharge act like U.V. light and decompose ozone molecules into oxygen atoms which then recombines with the undissociated  oxygen molecules to form Ozone. This mixture obtained is called ozonised oxygen and the apparatus used to prepare ozone is known as ozoniser . Mainly there are two types of Ozonisers and known ,  1- Siemens Ozoniser  2- Brodie's Ozoniser