electrochemistry & Intro, Faraday's Laws

Unit II

1. SANJIVANI K. B. P. POLYTECHNIC, KOPARGAON With NBA ACCREDIATED programs , Approved by AICTE, New Delhi, Recognized by Govt. of Maharashtra , Affiliated to Maharashtra State Board of Technical Education, Mumbai, ISO 9001:2015 Certified Institute Department:- Computer Technology Class:- First Year Name of Subject:- Basic Chemistry MSBTE Subject Code:- 22102

2. Syllabus 5.1 Electrolyte- Types of electrolyte, ionization and dissociation ,Cathode, Anode, Electrode potential: oxidation and reduction, Mechanism of electrolysis :Electrolysis, Electrochemical series for cations and anions. Mechanism of electrolysis of CuSO4 solution 5.2 Faraday’s laws of electrolysis: Faraday’s first and second law, relation between electrochemical equivalent and chemical equivalent, Numerical. Applications of electrolysis: Electro-refining of copper and Electroplating. 5.3 Difference between primary and secondary cell.

3. Electrochemistry Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

4. Electrochemistry - The branch of chemistry which deals with inter conversion of chemical & electrical energy. Conductor- The material which allows electric current to pass. Insulator- The material which does not allows electric current to pass. Electrode- A rod/wire/plate in contact with solution and conduct electricity inside or outside solution. Cathode-It is negative terminal of battery, during electrolysis. Anode- It is positive terminal of battery, during electrolysis. Electrolyte- The substance in fused or in aqueous solution gives ions and allows electric current to pass. Strong electrolyte & Weak electrolyte Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

5. Electrolysis- Decomposition of electrolyte in to ions by passage of electricity . Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

6. Electrode Potential- Potential arises on electrode either due to oxidation or reduction . 1. Oxidation potential- Potential due to oxidation(loss of electron) i.e. due to de- elctronation is oxidation potential . Ex. Zn electrode 2. Reduction potential- Potential due to reduction (gain of electron) i.e. due to electro nation is reduction potential. Ex. Cu electrode Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

7. Ionization & Dissociation Ionization- The process of splitting non electrolyte in to ions. Ex. HCl → H +  + Cl – * Dissociation- The process of splitting electrolyte in to ions. Ex. NaCl → Na +  + Cl – D egree of Ionization- The fraction of total number of molecule that undergo ionization at equilibrium known as degree of ionization Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

8. Electrochemical series for Cation/ Metal Electrochemical series are lists of metals in order of decreasing reactivity or ease of oxidation. The higher metals in the series, such as alkali metals and alkaline earth metals, are more reactive or more easily oxidised than the lower metals in the series. If Solution consist of more than one cation then cation from bottom discharge first. Cation with more concetration discharge first regardless of its position in series. During discharge at definite voltage only one cation can discharge. Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

9. Electrochemical series for Anion/ Non Metal Electrochemical series are lists of non metals in order of decreasing reactivity or ease of oxidation. If Solution consist of more than one anion then anion from bottom discharge first. Anion with more concetration discharge first regardless of its position in series. During discharge at definite voltage only one anion can discharge.

10. Faraday’s Laws of electrolysis First Law : - Weight of substance deposited or liberated at an electrode during electrolysis is directly proportional to quantity of electricity flowing through electrolyte . W α Q W = ZQ Where W= weight deposited, Z= electrochemical equivalent, Q= quantity of electricity W = ZIT ( Q = IT ) Where I = current in amp t = time in second If I = 1amp and t= 1 sec Then W = Z Electrochemical equivalent (Z) “ It is defined as weight of substance deposited or liberated when 1 ampere of current is passed for 1 Second .” Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

11. Second Law- When same quantity of electricity is flowing through different electrolyte connected in series, then weight of substance deposited or liberated at respective electrode is directly proportional to their chemical equivalent or equivalent weight Relation between Faraday’s First & Second law :- E = F Z Where E= equivalent weight Z= electrochemical equivalent F= Faraday 1F=96500C Z = E Faraday :- “Faraday is amount of electricity required to deposit or liberate 1 gram equivalent of substance at an electrode.” Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S. W1/W2 = E1/E2

12. Solved numerical Calculate the time in seconds in which 0.3 gms of copper is liberated from copper sulphate solution when a current of 0.5 ampere is passed (Eq. wt. of copper is 31.6) Given Data----- W= 0.3gm, I=0.5amp, E=31.6 i ] E.C.E. of Copper = Eq.Wt . of Copper / 96500 E = F Z = 31.6 / 96500 Z = 0.000327 gms /coulomb ii] From I st law of Faraday, w = Z It t = 0.3 / 0.000327 X 0.5 t = 1832 seconds. Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

13. A current of 4.0 amperes was passed through a solution of CuSO4 for 30 min. Calculate the amount of Cu deposited on the cathode (Eq. Wt. Of Cu is 31.77) Given : I = 04 amperes T = 30 min = 30 χ 60 = 1800 sec. C.E. of Cu is 31.77 To find: W =? C.E = 96500 χ E.C.E (Z) Z = C.E / 96500 = 31.77 / 96500 = 0.00032 gm /C From faradays first law W = z χ I χ t = 0.00032 χ 4 χ 1800 W = 2.370 gm Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

14. Same quantity of current was passed through CuSO4 & AgNO3 solution respectively. If 3.207 Gms Cu is deposited, calculate weight of silver deposited. Eq. Wt. Of copper = 31.77 & Eq. Wt. Of silver = 108 Given- W1- 3.207, E1= 31.77, E2= 108, W2 = ? W1/W2 = E1/E2 or W2/W1 = E2/E1 chemical equivalent of copper (E1) W2= E2/E1 W1 = 3.027 χ 108 / 31.77 = 10.290 g ms . Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

15. Application of electrolysis Electro refining- The process of obtaining pure metal from impure metal by the process of electrolysis is known as electro refining. electro refining of copper. At anode (+) - oxidation take place Cu  Cu +2 + 2e Impure blister At Cathode (-) - reduction take place Cu +2 + 2e-  Cu Pure ( deposits on pure strips) Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

16. Electroplating- Plating of more resistive metal like gold, silver etc. over inferior article by the process of electrolysis is known as electroplating. AgNO 3  Ag + + NO 3 At anode: oxidation ( dissolving of Ag rod ) Ag  Ag + + e- At cathode: Reduction (deposition of Ag over article) Ag + + e-  Ag↓ On article Purposes of electroplating:- To make article more decorative. To protect base metal from corrosion. To repair tools of machines Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

17. Primary & Secondary cell Cells are classified into two categories Primary cell- In this cell reaction occurs only for single time i.e. cell is non rechargeable. Cell reaction are irreversible. This cell is light in weight & chipper. Ex. Daniel cell, Dry cell etc. Secondary cell- In this cell reaction occurs for number of time i.e. cell is rechargeable. Cell reaction are reversible . These cells are heavy and expensive. Ex. Lead acid storage cell, lithinium battery etc. Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

18. Difference between primary and secondary cell Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.

19. Thank You Sanjivani K.B.P. Polytechnic, Kopargaon Department of Computer Technology Mrs. Bhattad K.S.