How Much Electricity in Terms of Faraday is Required to Produce Exercise Chapter 3 Electrochemistry Chemistry Class

Question 13:How much electricity in terms of Faraday is required to produce
(i) 20.0 g of Ca from molten CaCl₂.
(ii) 40.0 g of Al from molten Al₂O₃.

Answer:(i)  
The balance reaction will
The charge on Ca in CaCl₂
Ca + 2Cl      = 0
Cl has –1 charge so that
Ca  + 2(–1) = 0
Ca               = 2
We have to get 2o g Ca from Ca²⁺
Number of required moles  = mass / molar mass
Molar mass of Ca is 40 g/mol and required mass of Ca is 20 g
Hence number of moles           = 20/40      = 0.5 mol
Electricity required to produce 1 mol of calcium = 2 F
The electricity required to produce 0.5 mol of calcium
= 0.5 × 2 F
   = 1 F
(ii)
Charge on Al in Al₂O₃
2Al  + 3O = 0
Oxygen has –2
2Al +3(–2)   = 0
Al         = 3
Change transfer  n = 3
Charge required for 1 mol of Al    = 3F
Number of moles of Al  = 40 /27  = 1.48

The electricity required to produce 1.48 mol of Al = 1.48  × 3 F
= 4.44 F