chapter 5 electro chemistry semester II Diploma in Embedded systems

Electro chemistry

1. FACULTY DETAILS Name : DR. K. Shashank, Qualification : M. Sc., M. Phil., Ph.D. Designation : Head of General section Institution : GIOE, Secunderabad Scheme : C-18 Semester : I Sub. Code & Name : 18Common-104F, General Engineering Chemistry Topic, UNIT-V : ELECTROCHEMISTRY

2. RECAP In the last class we have completed the following topic: Arrhenius theory of electrolytic dissociation Electrolysis Electrolysis of fused NaCl and MgCl 2

3. UNIT – V: ELECTROCHEMISTRY Today’s topics: Applications of electrolysis Faraday’s laws of electrolysis

4. APPLICATIONS OF ELECTROLYSIS : E lectrolysis is a process of dissociation of electrolyte into ions under the influence of electricity. It is used mainly in several methods such as, 1. Purification or refining of metals and 2. Electroplating or electrolytic deposition etc.

5. 1. PURIFICATION OR REFINING OF METALS: T he impurities present in metal are separated by electrolysis process. This is called electrolytic purification or electrolytic refining. In this method, the impure metal to be purified is used as anode and a thin sheet of same pure metal is used as cathode. The same metal salt solution is taken as electrolyte. On passing electricity anode dissolves and pure metal ions of anode migrate to cathode. These ions gain electrons, get reduced and deposit at the cathode as pure metal. The impurities of anode settle at the bottom as anode mud.

6. Example: PURIFICATION OR REFINING OF COPPER In this method, a block of impure copper metal is used as anode and a thin sheet of pure copper is used as cathode. The acidified copper sulphate(CuSO 4 ) solution is taken as electrolyte. On passing electricity impure copper anode dissolves and copper ions(Cu +2 ) migrate to pure copper cathode. The copper ions gain electrons, get reduced and deposit at the pure cooper cathode. The impurities of copper anode settle at the bottom as anode mud. The following reactions occur during electrolysis i. At anode : Cu → Cu +2 + 2e - ( Oxidation) ii. At cathode: Cu +2 + 2e - → Cu ( Reduction )

7. Refining of copper:

8. 2 . ELECTROPLATING: The process of depositing a layer of superior metal on a base metal by means of electrolysis is called electroplating. In this method, the superior metal is used as anode and base metal is used as cathode. The salt solution of superior metal is taken as electrolyte. On passing electricity the anode dissolves and superior metal ions migrate to cathode. The superior metal ions gain electrons, get reduced and deposit over the cathode i.e., base metal. Example : Formation of silver layer on a copper spoon. In this method copper spoon is used as cathode and silver rod is used as anode. The aqueous solution of silver nitrate is taken as electrolyte.

9. ELECTROPLATING:

10. FARADAY’S LAWS OF ELECTROLYSIS: The relation between the quantity of electricity passing through and an amount of electrolyte was produced at an electrode was studies by Michael Faraday . The results were explained in the form of two laws, First law and Second law. I. FARADAY’S FIRT LAW: This law states that the amount of electrolytic substance produced at respective electrode is directly proportional to the quantity of columbic current passed through it. If W g of an electrolyte is produced by passing Q quantity of columbic current then according to this Law the relation between W and Q is given as below,

11. According to the first Law, W  Q W = e Q W = e c.t (where Q = c.t) W = e(ECE) ( where c = 1amp & t = 1sec) ( The amount of an electrolyte produced by the passage of 1 columbic current or 1amp current for 1sec time is called Electrochemical Equivalent (ECE) . Its units are gram per coulomb (g per C or g amp -1 sec -1 ) W = c.t (where e = ) W = c.t (where E = ) (E=equivalent weight, F=Faraday(96500 coulombs), Z=valency, GAW=gram atomic weight,)  

12. FARADAY’S FIRST LAW:

13. PROBLEMS : 1. The electrochemical equivalent of a metal is 0.00028g per coulomb. Calculate the weight of metal deposited by the passage of 10 amp of current for 10 minutes. Given data, c = 10 amp t = 10 min (10x60 =600sec) e = 0.00028 g/col. W = ? W = W = 0.00028x10x600 W = 1.68 g  

14. FARADAY’S LAWS OF ELECTROLYSIS: I I. FARADAY’S SECOND LAW: If same quantity of columbic current passes through different electrolytes arranged in series the amounts of electrolytic substances produced at respective electrodes are in the ratio of their chemical equivalents W 1 , W 2 , ….W n are the amounts of different electrolytes produced and E 1 , E 2 ,….E n are their chemical equivalents respectively, According to this Law the relation between weight(W) and chemical equivalent(E) is given as below, W 1 : W 2 ..….= E 1 : E 2 ……

15. According to the second Law, W 1 : W 2 = E 1 : E 2 = = = = ……. = = constant = constant ∴ W  E The amount of electrolyte(W) produced at an electrode is directly proportional to its chemical equivalent(E).  

16. PROBLEMS : 1. On passing same quantity of current through CuSO 4 and AgNO 3 arranged in a series 5.4 g of silver is deposited. Calculate the amount of copper deposited. Given data, weight of silver, W Ag = 5.4 weight of copper, W Cu = ? E Cu = = = 31.77 (Cu 2+ + SO 4 2- ) E Ag = = = 108 (Ag + + NO 3 - ) = W Cu = x = x = 1.5885 g  

17. Explain purification of copper by electrolysis What is electroplating? Explain with an examples State and explain Faraday’s first law State and explain Faraday’s second law FAQ s

18. In the next class will start the new chapter, UNIT – VI : ENVIRONMENTAL STUDIES - I FOLLOW UP

19. THANKYOU