complexs part 7

Distribution method
The method of distributing a solute between two immiscible solvents can be used to determine the stability con¬stant for certain complexes. The complexation of iodine by potassium iodide may be used as an example to illustrate the method. The equilibrium reaction in its simplest form is When iodine is distributed between water (w) at 25°C and carbon disulfide as the organic phase (o), as depicted in Figure 11-11, the distribution constant K(o/w) = Co/Cw is found to be 625. When it is distributed between a 0.1250 M solution of potassium iodide and carbon disulfide, the concentration of iodine in the organic solvent is found to be 0.1896 mole/liter. When the aqueous KI solution is an¬alyzed, the concentration of iodine is found to be 0.02832 mole/liter.
 In summary, the results are as follows:
Total concentration of I2 in the aqueous layer (free  + complexed iodine) = 0.02832 mole/liter
Total concentration of KI in the aqueous layer (free + complexed KI) = 0.1250 mole/liter.
Concentration of I2 in the CS2 layer (free) = 0.1896 mole/liter
Distribution coefficient, K(o/w) = [I2]o/[I2]w = 625
The species common to both phases is the free or uncomplexed io¬dine; the distribution law expresses only the concentration of free iodine, whereas a chemical analysis yields the total concentration of iodine in the aqueous phase. The concentration of free iodine in the aqueous phase is obtained as follows:
 To obtain the concentration of iodine in the complex and hence the concentration of the complex,  , one subtracts the free iodine from the total iodine of the aqueous phase:
 According to equation (11-22), I2 and KI combine in equimplar concentrations to form the complex. Therefore
 KI is insoluble in carbon disulfide and remains entirely in the aqueous phase. The concentration of free KI is thus