Chapter 122 of 2363 min read

Electrolysis and Faraday's laws; batteries and corrosion

Why this is asked: In aqueous NaCl electrolysis, Cl⁻ is oxidised at the anode instead of water, even though water's thermodynamic oxidation potential is lower — a real overpotential effect examiners like precisely because it contradicts the "always predict from E° alone" shortcut. Faraday's second law compares deposits by equivalent mass, not molar mass, so equal charge deposits different moles of ions of different charge.

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Test yourself

•The mass in grams of copper deposited by passing a current of 9.6487 A through a voltameter containing copper sulphate solution for 100 seconds is (given molar mass of Cu = $63 g mo l^{- 1}$ , 1 F = 96487 C):

•Match List I with List II.

List I (Conversion)	List II (Number of Faraday required)
A. 1 mol of $H_{2} O$ to $O_{2}$	I. 3 F
B. 1 mol of $Mn O_{4}^{-}$ to $M n^{2 +}$	II. 2 F
C. 1.5 mol of Ca from molten $CaC l_{2}$	III. 1 F
D. 1 mol of FeO to $F e_{2} O_{3}$	IV. 5 F

Choose the correct answer from the options given below:

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