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Electrochemistry

Question
CBSEENCH12005975
Wired Faculty App

How much electricity in terms of Faraday is required to produce
20.0 g of Ca from molten CaCl2?

Solution
            CaCl2 ⇌  Ca2+    +   2Cl-     Ca2++2e- →             Ca              2 mol                        1 mol ( = 40)                                                     (reduction of Ca2+) 
        40g of calcium needs = 2 mol of electrons = 2 Faraday.                                                                (∵ 1 mole of e = 1 F)
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 Ca 2+
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

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