CHEMISTRY NOTES

12^th Class Chemistry Notes

Solid State 

Solid: - Matter which posses rigidity having definite shape & volume is called solid.

Types of solid

1. Crystalline Solid :- Eg:- Metals And Non metals
2. Amorphous Solid :- Eg:- Rubber ,Glass ,Plastic

Difference and Comparison between characteristics of solid -
Crystalline Solid: - Contain regular arrangement having short range & as well as long range order.
Definite geometric shape, Sharpe melting point, they have definite heat fusion, they undergo clean cleavage, and they are true solid.
Amorphous Solid: - Containing irregular arrangement having short range order only, irregular shape, melting over range of temp, they do not have definite heat of fusion they undergo an irregular cut they are pseudo solid or super cooled solid.
Classification of crystalline solid:-
    1. Ionic Solid 
    2. Molecular Solid
    3. Covalent of network Solid
    4. Metallic Solid
(i) Ionic solid: - in these crystalline solids, constituent particle are positive or negative ion held together by columbic or electrostatic forces of attraction. Eg:-NaCl, MgO
(ii) Molecular solids:- These are of three types

1. Non polar molecular solid: - in these the constituent particles are atoms of noble gas or non polar molecules are held by London dispersion forces.
Eg: - Ar, H2.

2. Polar molecular solids: - In these solids constituent particles are held together by dipole-dipole attraction forces.
 Eg: - Hcl, SO2.

3. Hydrogen bonded molecular solids: - in these types of molecular solids constituent particles are molecule containing hydrogen linked to F, O and N held by hydrogen bonding.
Eg: - H2O (ice), NH3.

(iii) Covalent or Network Solids: - Constituent particles are atoms held together by covalent bonds. Eg: - C (diamond), SiO2 (quartz).
(iv) Metallic solids: - Constituent particles are positive ions in a sea of mobile electrons held together by metallic bonds. Eg: - All metals and alloys.
Crystal Lattice: - Regular arrangement of constituent particles in 3-D is called crystal lattice or space lattice.
Unit cell: - The smallest three dimensional portion of a complete space lattice which when repeated over and again in different direction produces the complete space lattice is called unit cell.
Bravais lattice: - The fourteen lattices corresponding to seven crystal system are known as Bravais Lattice.
Coordination number: - the number of spheres touching to a particular sphere.
No. of atoms per unit cell:-
(a) No. of atoms in simple cubic lattice:- 8 atoms are at corner
       8*1/8=1                                                                          


(b) No. of atoms in BCC:- 8 atoms are at corner and one in the body
         8*1/8+1+2    
                                             
(c) No. of atoms in FCC:- 8 atoms are at corner and six atoms are at faces (one on each face)
        8*1/8+6*1/2=4

                                                       
Close packing in crystals:-

1. Close packing in one dimension: - sphere are touching each other in a row. In this arrangement coordination no. is 2

                                              

2.  Close packing in two dimension:- it is done by two ways-
1. Square close packing: - in this arrangement spheres of second row are exactly above the first row.
               

2. Hexagonal close packing: - in this arrangement the spheres of second row may be placed in the depression of the first row.
    
3.  Close packing in three dimension
1. Three dimensional close packing from two dimensional closed packed layer: - starting from the square close packed layer the second layer and all further layers will be built up such that they are horizontally as well as vertically aligned with each other.


2. Three dimensional packing from two dimensional hexagonal close packing:- when spheres are arranged in hexagonal close packing in 2-Dthe two types of voids ‘a’& ‘b’ are formed.
‘a’ & ‘b’ voids are triangular when second layer is placed over the void of first layer (only one void is full filled) in hexagonal close packing and these layer form two voids
C – Triangular and D – Octahedral.
Packing efficiency: - The percentage of the total space filled by the particles is called packing efficiency.
Packing fraction: - The fraction of the total space filled is called packing fraction.

SOLUTION

Solution: - A solution is homogeneous mixture of two or more chemically non-reacting substances, whose composition can be varied within certain limits.

Expressing concentration of solutions

1. Percentage:-
• mass percentage (%) of a component  (W/W)
                  = Mass of the component in solution*100 / Total mass of the solution

• volume percentage (%) of the component (V/V)
           = Volume of the component * 100 / Total volume of the solution

• Mass/Volume percentage (%) of the component (W/V)
           =Mass of the component in solution * 100 / Total volume of the solution
2. Strength:-
Strength of the solution ( gl^-1 or gdm^-3) = Mass of the solute in grams / Volume of the solution in litre
3. Molarity (M) :- No. of moles of the solute  / Volume of the solution in litre
    M = strength in gram per litre / Molar mass of the solute
4. Mole fraction :-  It is obtained by dividing the no. of moles of the solute or solvent by the total no. of moles of the solution.
Mole fraction,    X₁ = n₁/n₁+n₂
                      X₂ = n₂/n₁+n₂
 n₁ = no. of moles of the solvent
 n₂ = no. of moles of the solute
X₁+X₂ = 1
5. Mass fraction: - Mass of the given component per unit mass of the solution denoted by X.
Mass fraction,   X_A = W_A / W_A+W_B
                      X_B = W_B / W_A+W_B
W_A = Mass of the solvent
W_B = Mass of the solute
X_A+X_B = 1

Solution of solids in liquids

• Solubility of a solid in a liquid :- It is defined as the maximum amount of the solid (solute) in grams which can dissolve in 100 grams of liquid (solvent) to form the saturated solution at the particular temperature.

Factors affecting the solubility of a solid in a liquid

1. Nature of the solute & the solvent :- “Like dissolves Like”
• The polar (ionic) compounds like NaCl dissolve in polar solvent like water.
• The non polar (covalent or organic) compounds dissolve in non polar compounds like Anthracene dissolve in Benzene.
2. Effect of temperature :-
• The solubility increases with increase of temperature when the process of dissolution is endothermic.
Solute + Solvent + Heat ----> Solution
Ex:- NaNo3, KNO3, NaCl, KCl
• The solubility Decreases with increase in temperature when the process of dissolution is exothermic.
Solute + Solvent -> Solution + Heat
              Ex:- Sodium carbonate mono hydrate (Na2CO3.H2O).
• Those whose solubility does not increases or decreases continuously
Ex:- CaCl2.6H2O -> CaCl2.4H2O -> CaCl2.2H2O

Solution of Gases in liquids

• Solubility of a gas in a liquid :- The solubility of a gas in a particular liquid is the volume of the gas in CC’s (centimetre cubes cm³) that can dissolve in unit volume of the liquid to form the saturated solution at the temperature of the experimented under a pressure of one atmosphere.

Factors affecting the solubility of a liquid in a gas

1. Nature of the gas & the solvent:- Gases like Hydrogen, Oxygen, Nitrogen etc. dissolve in water only to a small extent but gases like CO₂, HCl, NH₃ are highly soluble. The greater solubility of later gases they react with solvent. the greater solubility of the gas in a solvent due to their chemical similarity.
2. Nature of temperature:- The solubility of gases decreases with increase  in temperature.
3. Effect of pressure (Henry’s Law):- By increasing the pressure solubility also increases.

Henry’s Law:- The mass of a gas dissolved in the given volume of liquid at constant temperature is directly proportional to the pressure of the gas present in equilibrium with the liquid.
                                        m ∝ p
                                        m=K_HP
Also,
The partial pressure of gas in vapour phase (P) is proportional to the mole fraction of gas (x) in the solution.
                                    P=K_HX

Limitations of Henry’s law

Henry’s law is applicable only if the the following conditions are satisfied:-

• Pressure should be low and temperature should be high i.e. gas behaves as an ideal gas.
• The gas should not go under compound formation with solvent or association or dissociation in the solvent.
  

  Electrochemistry

  Electrolysis: It is the process of decomposition of an electrolyte by the passage of electricity through its aqueous solution or molten state.

  Faraday’s first law of electrolysis

  In a chemical reaction, the amount of any substance deposited or librated is directly proportional to the quantity of electricity passed through it.
                                      W ∝ Q
                                      W = ZQ                                   
                                      W = Zit                                            ( Q= I*t )
  Where, Z = Electrochemical Equivalent.
  Z = atomic weight/nF                   (n = no. of electron, F = 96500 )

  Faraday’s second law of electrolysis

  When the same quantity of electricity is passed through the different electrolytes connected in series. The weights of the substance produced at the electrodes are directly proportional to their equivalent weights.
              Ex: AgNO₂  and CuSO₄ solution connected in series,
  
  Conductance of electrolytic solution:- Electrolytes conducts electricity by decomposition.
  Electrical resistance:- If voltage v is applied to the ends of the conductor and current “I” floe through it, then the resistance “R” of the conductor is V/I (ohm).
  Electrical conductance:- The reciprocal of electrical resistance is called conductance. And is represented by G sign
  Thus,    G = 1/R                              [unit of G = mho]
  Specific resistance or Resistivity:- it is observed that,
                                      R ∝ l                                   
  There r is constant and called as resistivity.
  Specific conductance or conductivity:- The reciprocal of resistivity is known as conductivity. And is denoted by k (kappa).
                          R=1/G              or,        r = 1/k     ……………………(i)
      ……………………………..(ii)
  From eq. (i) and (ii)
  
  

  Equivalent conductivity

  Equivalent conductivity:- equivalent conductivity of a solution at a dilution v is defined as the conductance of all the ions produced from one gram equivalent of the electrolyte dissolved in v cm3 of the solution when the distance between the electrode is one cm and the area of the electrode is so large then whole the solution is come between them. It is represented by
  Equivalent conductivity = Specific conductivity ´ v
                                                 
                                                            
  Where, Ceq is concentration of solution in gm. eq/L.
  
  But, for particular cell ‘l/a’ is constant called cell constant and is represented by G*
  
  
                                       
  Where, c is molar concentration.
  

  Chemical Kinetics

  The branch of chemistry, which deals with the study of reaction rates and their mechanism, called as chemical kinetics.
  Rate of a chemical reaction:- “ The rate of a reaction can be defined as the change in concentration of a reactant or product in unit time”
  Let a reaction whose volume remain constant                    R -------> P
  One mole of reactant R produces one mole of product P. [R1] & [P1] and [R2] & [P2] are the concentrations of R & P at time t1 & t2 respectively.
  Then,                    Δt =t2-t1
                              Δ[R] = [R2]- [R1]
                              Δ[P] = [P2] – [P1]
  Where,                 square brackets show molar concentration.
   ……………………….(i)
   ……………………….(ii)
  Both above expression show average rate of reaction.
  Units of rate of reaction:-
• Concentration     time^-1
• Mol                   L^-1s^-1

Instantaneous rate of reaction:- It is the rate of change of concentration (i.e. change of concentration per unit time) of any one of the reactants or products at that particular instant of time.
                               
Factors influencing Rate of a reaction:-

• Concentration:- As concentration of reactant increase, rate of reaction also increases.
• Temperature:- Rate of reaction increases with increase of temperature mostly reaction rate double with rise of 100 temperature.
• Catalyst :- Catalyst generally increase the rate of reaction without undergoing in the reaction, it also help in attaining the equilibrium quickly without disturbing the equilibrium state in reversible reaction.

Rate expression and rate constant:-

Consider a general reaction aA + bB --------> cC + dD
Where,         a, b, c, and d are stoichiometric coefficient of reactants and products.
The rate expression for this reaction is-
                                                                             Rate ∝ [A]^x [B]^y  ………………………..(iii)
Where,         component x & y may or may not be equal to the stoichiometric coefficient (a & b) of the reactants
Also,              Rate = k [A]^x [B]^y   ………………………………(iv)
                        ………………………………(v)
This form of equation (v) is known as differential rate equation, where k is proportionality constant called rate constant. And the equation (iii) which relates the rate of a reaction to concentration of reactants is called Rate law or rate expression.

Rate:- Rate law is the expression in which reaction rate is given in terms of molar concentration of reactants with each terms raised to some power, which may or may not be same as the stoichiometric coefficient of the reacting species in a balance chemical reaction.
EX:-  Reaction ® Experimental rate expression

• CHCl₃ + Cl₂ --------> CCl₄ + HCl

        Rate = k[CHCl₃] [Cl₂]^1/2

• CH₃COOC₂H₅ + H₂O -----------> CH₃COOH + C₂H₅OH

        Rate = k[CH₃COOC₂H₅]¹ [H₂O]⁰

• 2NO + O₂ ---------> 2NO₂

Order of a reaction:- The sum of powers of the concentration of the reactants in the rate of low expression is called as the order of that chemical reaction.
Rate = k [A]^x [B]^y
Order = x+y
Order of reaction may be 0, 1, 2, 3 or even in fraction, Zero order reaction is independent of concentration.

Unit of rate constant (k):-
                aA + bB -------> cC + dD
  Rate = k [A]^x [B]^y
Where,                                 x+y = n = order of reaction
               
       
For zero order reaction,
                                Order = n = 0

                                 
For first order, n = 1
                               
                                               
For second order, n = 2
                               
   = Mol^-1 L s^-1

• Surface Chemistry 

  Adsorption: - The accumulation of molecular species at the surface rather than bulk of solid or liquid is called Adsorption.
  Adsorbate: - The molecular species or substance which accumulate at the surface.
  Adsorbent: - The surface of material on which Adsorption takes place.
  Desorption: - The process of removing of adsorbed substance from the surface on which it is adsorbed.
  Absorption: - When the molecular species or substance enters in the bulk phase in solid or liquid is called as Absorption.
  Sorption: - When both adsorption and absorption takes place simultaneously is called as sorption process.

  Mechanism of Adsorption

  Inside the Adsorbent (in bulk) the force acting between the particles are mutually balanced but on the surface, the particles are not surrounded by atoms or molecules of their kind on all sides and hence they posses attraction force so particle stick on the surface of the Adsorbent.
  The extent of adsorption increases with increase in surface area per unit mass of the adsorbent at a given temperature and pressure.
  Heat of adsorption: - With increase in heat Adsorption process decreases.
  Adsorption equilibrium: - As the molecules of the adsorb ate are held on the surface of the solid adsorbent.
  Entropy decreases, i.e. DS is negative
  
  For the process of adsorption to occur, DG must be negative which is possible only when, DS keeps on decreasing and TDS keeps on increasing till ultimately DH becomes equal.
  To TDS so that DG = 0, this state is called adsorption equilibrium.

  Types of adsorption

  There are two types of adsorption
• Physical Adsorption or physisorption: - If accumulation of gas on the surface of solid occurs on account of weak vanderwalls forces is called physical Adsorption.
• Chemical Adsorption or chemosorption: - When gas molecules or atoms are held to the surface (solid) by chemical bonds, the Adsorption is called Chemical Adsorption.

 Characteristics of physical Adsorption or physisorption

• Lack of specificity: - A given surface of an Adsorbent does not show any preference for a particular gas as the vanderwalls forces are universal.
• Nature of Adsorbate: - The amount of gas Adsorbed by a solid depends on the nature of the gas.
• Reversible nature: - Physisorption is reversible because adsorbate may be removed by decreasing pressure.
• Surface area of Adsorbent: - Physisorption increases with increase in surface area.
• Enthalpy of Adsorption: - Physical Adsorption is exothermic process but its enthalpy of adsorption is low (20-40 KJ mol-1).

Characteristics of Chemical Adsorption or chemosorption

• High specificity: - It is high specific because it occurs if there is some possibility of chemical bonding.
• Irreversibility: - As chemisorptions involve compound formation, so it is usually irreversible process.
• Temperature: - Chemisorptions increases with increase in temperature after saturation starts decreasing.
• Pressure: - it is also increases with increase in pressure.
• Surface area: - chemisorptions increases with increase in surface area.
• Enthalpy of Adsorption: - Enthalpy of chemisorptions is high (80-240 KJ mol-1) as it involves chemical bond formation.

• General principle and process of isolation of the elements

  Minerals: - These are naturally occurring chemical substances in the in the earth crust obtainable by mining.
  
  Ores   : - only few minerals are used as sources of that metal. Such minerals are known as ores.
  Gangue: - ores are usually contaminated with earthly or undersides materials known as gangue.
  Metallurgy: - The entire scientific and technological process used for isolation of the metal from its ores is known as metallurgy.
  Concentration of the ore: - the removal of earthy and siliceous impurities (i.e. gangue or matrix) from the ores is called concentration of ores.
• Hydraulic washing: - The processes by which lighter earthy particles are free from the heavier ore particles by washing with water.
• Magnetic separation: - This method of concentration is  employed  when  either the ore or impurities associated with it are magnetic in nature. Example: - chromate.
• Froth floatation: - This method is based upon the fact that surface of sulphide ores is preferentially wetted by oils while that of gangue is preferentially wetted by water.
• Leaching: - this process consists in treating the powdered ore with a suitable reagent which are selectively dissolved the ore but not the impurities.

Leaching of Alumina from bauxite: - Ore of aluminium, bauxite usually contain  SiO₂, iron oxide, TiO₂, as impurities .the concentration is carried out by digesting the powdered ore with the concentrated solution of  NaOH  at 473 to 523 K and 35-36 bar pressure. This way Al₂O₃ is leached out as sodium aluminates behind.
3H₂O+Al₂O₃+2NaOH   ----------->  2Na[Al(OH)₄]
The aluminates in solution is neutralised by passing CO₂ gas and hydrated  Al₂O₃ is precipitated.
2Na[Al(OH)₄]+CO₂  ------------>  Al₂O3*xH₂O + 2NaHCO₃ 
NaHCO₃ remains in the solution and hydrated alumina is filtered, dried and heated to give back pure Al₂O₃.

Other Examples: -   In the metallurgy of silver and that of gold , the respective  metal is leached with a dilute solution of NaCN or KCN  in the presence of air (for O₂) from which the metal is obtained later by replacement.

Where M = Ag or Au.
4[M(CN)₂]- + Zn  ----------->  [Zn(CN)4]2- + 2M

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