HYDROLYSIS OF LEADII AND ITS EFFECT ON THE SOLUBILITY OF LEAD IODATE

Sn^II and Ph^II are found to be more hydrolysed in aqueous solution than some other divalent ions of comparatively smaller radii. The hydrolysis in some cases depends on the capacity of the cation to farm covalent bond, besides on charge and radius. The hydrolysis of divalent lead ion might

be represented by,                                          Pb²⁺+ H₂O\(\rightleftharpoons\) PbOH⁺+ H⁺                                               ...(1)

and                                                                 PhOH⁺+ H₂O\(\rightleftharpoons\) Pb(OH)₂+H⁺                                         ... (a)

taking place in two steps. The extent of hydrolysis depends on the activity of water, and therefore expected to he appreciable in very dilute solution of lead salts. In a saturated aqueous solution of lead iodate, the hydrolysis is found to be appreciable and ₄S³ (where S is the solubility of lead iodate in g. mole per litre at a given ionic strength at 35°) does not represent the solubility product of lead

iodate. ₄S³ is equal to K_s x [H⁺]+ Ks x k (where K. is a constant, Is is the equilibrium constant of the reaction (z) and [H+] is the molar concentration of hydrogen ion). Hence ₄S³ at lower P_H is hydrogen-dependent, whereas at higher P_H, the factor K_s x [H⁺] being smaller compared to K_s . k₁, it is independent of tn. The mean value of k is 0.121.