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Electrochemistry XI
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Primary and Secondary batteries

Shaillee Kaushal is teaching live on Unacademy Plus

Shaillee Kaushal
Faculty in Chemistry with a teaching experience of 14 years. Specialised in teaching for boards and competitions.

U
Unacademy user
sir plzzzz hindi medium valo ke liye bhi bnaye lesson......apke lgbhg sare lesson in englisg
mam plz upload surface chemistry lessons soon.. also.. in that there is a doubt about the zeta potential and helmholtz double layer..
  1. XII - 03 ELECTROCHEMISTRYXI


  2. Batteries There are two kind ofbatteries: (i) Primary Batteries: These batteries are non-rechargeable batteries. These connot be charged once they become non operational (ii) Secondary Batteries: These are chargeable Batteries. By reversing the reactions they can be recharged


  3. Primary voltaic cell- Dry cell: Metal cap Seal Graphite (cathode) Anodereaction: MnO2+C Zn Zn2+ + 2e- The electrons are utilized at carbon rod (cathode) as the ammoniumions are reduced Cathode: Paste of NH,CI+ ZnCla 2NH + 2e- 2NH3 + H2 Zn + 2NH+ Zn2+ + 2NH3 + H2 3Mn02 H22Mn0(OH) nc anode The cell reaction is: Hydrogen is oxidized by MnO2 in the cell:- Ammonia produced at cathode comines with zinc ions to form complex ion: Zn2+ + 4NH3 [Zn(NH3)4]2+ Eceli 1.6 volt


  4. Button cell In this cell: Cathode- mercuric oxide plus carbon paste Anode = zinc Electrolyte paste of ZnO and KOH The cell process is given below Anode: Zn 20HZno H202e Cathode: Hgo +H20+2e--Hg+ 20H- Overal Hg0 +Zn-Zn0+Hg The potential of this cell is 1.35 volt


  5. At anode:- Anode Pb2+ combine with sulphate ions to form insoluble PbsO4 Pb2+ + SO2PbSO4 (Precipitation) Cathode At cathode: Pb02 4H+2e- Pb2+ 2H20 Pb plates PbO2 plates Overall cell reaction: Pb+ Pb02 4H 2S022PbSO4 Eell 2.041 volt 2H20 Aqueous H2SO, During Recharge of the battery:- >The electrochemical cell becomes electrolytic cell 2PbSO, + 2H20-, pb + PbO2 + 2H,so,


  6. At anode Cd(s) + 2OH- Cd(OH)2 + 2e- At cathode Ni02 + 2H20 + 2e--> Ni (OH)2 + 20H' Overall reaction Cd Nio2 2H20Cd(OH)2 +Ni(OH) In the recharging of the cell Cd(OH): + Ni (OH)2 Cd(s) + Ni02 + 2H20 Positive plate Negative Separator plate


  7. At anode: H20 Anode t Cathode At cathode: 02 2H20 ne 40H overall 2H2 + 0,-2H20 reaction 02 These type of cells are used in space crafts Fuel cells are efficient and pollution free Thermodynamic efficiency of full cells: . Electrolyte Porous carbon electrodes


  8. Concentration cells If two plates of same metal are dipped separately into two solutions of the same electrolyte and are connected to the salt bridge, the whole arrangment is found to act as galvanic cell. In general there are two types of concentration cells:


  9. (i) Electrode concentration cells: In these cells, the potential difference is developed between two electrons at different concentration dipped in the same solution of the electrolyte. For example, two hydrogen electrodes at different pressures in the same solution of hydrogen ion constitute a cell of this type. 0.0591, P cell log 2 P2 If concentration are considered , 0.0591, 2 log


  10. (ii) Electrolyte concentration cells:- In these cells electrodes are identical but these are mersed in solutions of same electrolyte of different concentrations The source of electrical energy in the cell is the tendency of the electrolyte to diffuse from a solution of higher concentration to that of lower concentration. -At start the emf of the cell is maximum and it gradually falls to zero (C2 > C1) Anode Cathode = 0.0591 log cell The concentration cells are used to determine the solubility of sparingly soluble salts, valency of cation of the electrolyte and transition point of two allotropic forms of the metal used as electodes.