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XII- 03 Electrochemistry -II
Faradav's Law for Gaseous electrolvtic Product. _ItM nF This equation is used to calculate the mass of solid substance dissolved or deposited at the electrode. For gases, we use It Ve 96500 V volume of gas evolved Ve- Equivalent volume volume ofgas evolved at an electrode at S.T.Pby 1 faraday charge
For e.g: 02: M = 32 E=8 32g 02 = 22.4L STP 8g of 02 5.6L at S. T. P Ve of 02 5.6 L at STP Cl2iM = 71,E = 35.5 71g Cl2 22.4 L 35.5g of Cl2 11.2 L Ve = 11.2 L at STP
Faraday's laws of electrolvsis: Faraday gave the relationship between quantity of electric charge passed through an electrolyte and the amount ofsubs tance deposited a the electrode in 1 8 3 4 . (i Faraday's 1st law: When an electric current is passed through an electrolyte, the amount of substance deposited is proportional to the quantity ofelectric charge passed through the electrolyte Mathematically: w mass of substance deposited Q-charge flowing through the cell Q-It Z-electrochemical equivalent. It can be defined as the mass of the substance deposited when 1 ampere of current flows through the cell in one second Now M- Atomic mass of the substance n-no. of electron exchange F 96500 C. nF
Faraday's second law When the same quantity of charge is passed-through different electrolytes, then the ratio of different substances deposited at the different electrodes will be in ratio oftheir equivalent vessel. SO, Solution CusO, Solution AgNO, Solution
As shown in the above figure different electrolytes are taken in three different voltmeters containing solutions of H2S04,CuSO4,AgNO3 respectively. In the first, hydrogen and oxygen will be liberated, in the second copper will be liberated and in the third silver will be deposited Mass of hydrogen Mass of copper Eq.mass of hydrogen Eq.mass of copper mass of copper Eq.mass of copper Eq.mass of silver mass of silver mass of silver Eq mass of silver Eq mass of hydrogen mass of hydrogen 96500 c of electric charge will deposit one g-equivalent of any substance. 96500 C is termed as one Faraday andis denoted by F According to this law: Z, E
Applications of electrolysis: 1. Determination of equivalent masses of elements: WA Equivalent mass of A Equivalent mass of B WB Knowing the equivalent mass ofone element the equivalent mass ofother element can be calculated.The equivalent masses of those non-metals which are evolved at anodes can also be determined by this method.
2. Electrometallurgv: The metals like sodium, potassium, magnesium calcium, aluminium etc. are obtained by electrolysis of fused electrolytes. Fused electrolvte NaCl CaCl2 KF CaCl2 +CaF2 Al203 cryolite MgCl2 Nacl CaCl2 NaOH KC CaCl2 Metal isolated Na Ca Al Mg Na 3.Manufacture of non-metals:- Non-metals like hydrogen, fluorine, 3 chlorine are obtained by electrolysis.
4. Electrorefining of metals:_The metals like copper ,silver, gold, aluminium are refined by electrolysis. 5. Manufacture of comounds: Compounds like NaoH. KOH, Na2 , KC103, white lead, KMnO, etc. are manufactured by electrolysis.
6. Electroplating The process of coating an inferior metal with a superior metal by electrolysis is called electroplating. The object to be electroplated is made the cathode and the block of metal to be deposited is made the anode in an electrolytic cell containing a solutionofa salt of anodic metal. On passing current in the cell the metal of the anode dissolves out and is depositedon the cathode article in the term form ofa thin film. For electroplating With copper With silver With Nickel With Gold With Zinc With tin Anode Cu Cathode Object Object Object Object Iron object Iron object Electrolyte CuSO4 + dilute H2SO4 KAg(CN)2 Nickel ammonium sulphate Au Zn Sn KAu(CN)2 ZnSO4 SnSO