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1.What is meant by redox reactions ?  

Simultaneous occuring of reduction and oxidation reaction is known as redox reaction.

     2 H2 + O2  → 2 H2O.

2. What is the classical concept of redox reaction ?

 Oxidation reaction: Addition of oxygen  .       C + O2    →   CO2.

 Reduction reaction: Addition of hydrogen   .  N2 + 3 H2    →   2 NH3.

3. What is redox reaction in terms of electron transfer ?

   Oxidation: Losing of electrons

  Reduction: Gaining of electrons

eg:- Mg → Mg2+ + 2e -

       O  → O + 2 e

       Mg2+ + O2- → MgO

Here Oxygen is oxidising agent and Mg is reducing agent.

4. Define oxidation number ?

 It defines the state of oxidation of an element in a compound calculated according to a set of rules formulated on the basis that electrons in the covalent bond entirely belong to more electronegative element.

5. Write down some common rules of oxidation number?

  1. In the free state the oxidation number of an atom of an element is zero. eg:- Na, Ag, H2, N2, O2
  2. The oxidation number of an ion is same as its charge. eg:- Na+, K +   Here oxidation number is +1.
  3. The oxidation number of hydrogen is all its its compound is +1 except in ionic hybrids where oxidation number is - 1. eg:- LiH   Li = +1 , H = -1
  4. The oxidation number of fluorine is always -1.
  5. Oxidation number of oxygen is - 2.
  6. In peroxides oxidation number of oxygen is - 1
  7. In oxifluorides oxidation number of oxygen is + 2.
  8. Oxidation number of alkali metals is always + 1.
  9. Oxidation number of alkaline earth metals is + 2.
  10. The algebraic sum of oxidation number of all the atoms in a molecule is zero. eg:- H2O
  11. The algebraic sum of oxidation number of all atoms in an ion is equal to the charge on ion.

6. What is the redox reaction in terms of oxidation number ?

     Oxidation : Increase in oxidation number means oxidation

    Reduction : Decrease in oxidation number means reduction

7. What are the types of redox reactions ?       

  1. Combination redox reaction
  2. Decomposition redox reaction
  3. Displacement redox reaction
  4. Disproportioation redox reaction

8. What is meat by combination redox reaction ?

    The reaction in which two substance combine together to form a new compound.


9. What is meant by decomposition redox reaction ?

  The reaction in which a compound breaks up into two or more substances.


10. What is meant by displacement redox reaction ?

            Ab + C → AC + b

  • Metal displacement reaction:  
  • Non-metal displacement reaction: 

11. What is disproportionation redox reaction ?

   This involves the simultaneous oxidation and reduction of an element in one oxidation state.


12. Write the steps for balancing of redox reactions using oxidation number method ?

  1. Write the skeletal equation for all the known reactants and products of the reaction.
  2. Indicate the oxidation number of all the atoms in each compound in the skeletal equation and ignore the atoms or group in which there is no change in oxidation number.
  3. Now identify the atoms undergoing change in oxidation number. calculate the increase or decrease in oxidation number per atom and then for the whole molecules in which it occur. If these are not equal, then multiply by suitable co-efficient so that these become equal.
  4. Balance the chemical equation with respect to all atoms except hydrogen and oxygen.
  5. Finally balance with respect to H2 and O2. For balancing O atom add H2O molecules to the deficient side. balancing of H atom depends upon the medium (acidic / basic).
  • If the reaction is in acidic medium, the deficiency in H atom can be made up by adding H+ ions in deficient side.
  • If the reaction is in basic medium, the deficiency in H atom can be made up by adding H2O molecules  on deficient side and adding equal number of OH - ions on the other side of the equation.

                       Finally the equation is balanced by cancelling common species present on both sides in the equation.

13. Define electricity ?

   The process of transfer of electrons is called electricity.

14. Define current ?

  The process of transfer of charge is called current.

15. What is electrochemical cell ?

  A cell that converts chemical energy into electrical energy and viceversa.

16. Explain about galvanic cell ?      


                       Take two beakers filled with ZnSO4 and CuSO4 solution. Dip Zn rod and Cu rod in ZnSO4 and CuSO4 solutions respectively. Now connect the beakers with the help of a salt bridge. The two rodes are connected internally using a wire with a galvanometer fixed. Zn undergoes oxidation and Cu undergoes reduction. Zn gets deposited on Cu. As a result,

In anode,  Zn →  Zn2+  +  2e-

In cathode,  Cu2+  + 2e-  →  Cu

17. What is salt bridge ?

  Salt bridge consists of a jelly like substance called Agar - Agar with potassium nitrate and Ammonium chloride.

18. What is electrode potential ?

   When an electrode is dipped in salt solution, the electrode has a tendency to loss electrons and the solution has the tendency to gain electrons.Electrons move from lower electrode to higher electrode potential.

19. What is oxidation potential ?

  The ability of the electrode to gain  electrons is called oxidation potential.

20. What is reduction potential ?

  The ability of the electrode to lose  electrons is called reduction potential. In IUPAC, naming reduction potential is called electrode potential. The electrons move from anode to cathode.

21. What is Standard Electrode Potential ?

   The electrode potential at standard condition ( 1 atm, 293 K ) is called standard electrode potential.

a) The electronic configuration of group 14 elements is ns2 np2 .So the most common oxidation state exhibited by them should be +4 .+2 oxidation state is more and more common. On  moving down the group the higher oxidation state becomes less stable .This is because of the inert pair effect .Thus Ge ,Sn,and Pb show both the +2 and +4 oxidation states ,the stability of the lower oxidation state decreases on moving down the group .
                         C   Si   Ge   Sn  Pb >
(stability of +2 state  increases and +4 state decreases)    

b) Boric acid is not a pro-tic acid .It is a weak mono basic acid ,behaving as a lewis acid.
It behaves as an acid by accepting a pair of electrons from OH- ion .

c) Substances which reduces the other substance and oxidises itself  that is losses electrons and increases its on are reducing agents .A good reducing agent will easily oxidises itself and easily losses electrons .
In the reaction ,
    Cl2 + SnCl2 _________ > SnCl4 ,SnCl2 oxidised to SnCl4 and Cl2 reduced to Cl4 .

d)Flo urine atoms have filled 2p orbitals that can overlap with the empty 2p orbital  on the boron atom to give some double bond character to the B-F bonds  .As a result of the contribution by resonance structures having double bond character ,the boron atom in BF3 is not as electron deficient as it is in BCl3 .So BCl3 is better lewis acid than BF3  .

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