How much electricity in terms of Faraday is required to produce

Q.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.

Solution:

(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 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

(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