The Distribution Coefficient of Iodine Between Water and Tetrachloromethane

1 The distribution coefficient of iodine between water and tetrachloromethane 

When a solute is in equilibrium with two immiscible liquids at a given temperature, the ratio of the concentrations of a given species of the solute in the two liquids is constant and independent of the amount of solute. This ratio is termed the distribution coefficient 

When iodine is in equilibrium with water (w) and the immiscible CCI4 (0), D is given 

For the determination of D, the volume of water is conveniently taken as 8 times the volume of the organic liquid in which iodine is much more soluble than in water. The concentration of iodine in each liquid can be easily determined by titration against thiosulphate. 

When iodine in the aqueous layer reacts widi iodide in the aqueous solution, die triiodide ion is formed in equilibrium with die two reactants. If such an aqueous solution is equilibrated with the organic solvent used above, the constant D iqiplies to molecular iodine. Using the determined D and die results of equilibrium mixtures of iodine and KI in the aqueous layer and in CCI4, the equilibrium constant of the above reaction can be determined. 

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