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[5] POLYVALENT ION HYDROLYSIS:

(1) POLY ANION HYDROLYSIS:(Poly acidic base):
For example PO4-3 (n=3) , C2O4-2 (n=2), S-2 (n=2) , N-3 (n=3) etc.
Na2S, NH3PO4, Na3PO4   (Hydrolysis is study just like hydrolysis of polybasic acids / polyacidic base) we know that dissociation constant of phosphoric acid is given as:

DISSOCIATION CONSTANT OF PHOSPHORIC ACID:

Step-1
Step-2
Step-3
HYDROLYSIS OF ANION (PO4-3):
Step wise illustration of hydrolysis of poly basic acids and polyacidic base is given as - 
Step-1
Experimentally we know that   Ka1>>Ka2>>Ka3, hence x >>y>>Z   so y and z can be neglected with respect to x 
Special Case (1):  
Special Case (2)
          then x can be calculate by quadratic equation. 
Step-2
Experimentally we know that   Ka1>>Ka2>>Ka hence   x>>y>>Z    So y and z can be neglected with respect to x and the x present in denominator and numerator both  are cancelled .
Step-3
Experimentally we know that   Ka1>>Ka2>>Ka hence   x>> y>>Z  So y and z present in numerator can be neglected with respect to x and the z present in denominator is also neglected with respect to y.
Finally -  
And concentration of different species  
 (2) POLY CATION HYDROLYSIS: (Poly basic acid):
For example Ca+2 , Fe+3 , Al+3 , Mn+2 , Cd+2  , Zn+3  etc
ILLUSTRATIVE EXAMPLE:
Calculate pH and concentration of all species in 0.1 M solution of FeCl3 given Fe(OH)3 have  Kb1=10-3 , Kb2=10-7 and Kb3=10-12.

SOLUTION:
  Fe+3 àundergo hydrolysis while, Cl-  à do not under goes hydrolysis.

   We know that 
Experimentally know that Kb1>>Kb2>>Kb3      so x>>Y and Y>>Z
Hence y and z neglected with respect to x
HYDROLYSIS OF FeCl3:
Experimentally we know that   Ka1>>Ka2>>Ka3 ,   hence  x>>y>>Z    So  y and  z can be neglected with respect to x

TITRATION BASED POLYVALENT ION HYDROLYSIS:

(1) TITRATION OF Na2CO3 Vs HCl:
(2) TITRATION OF NA3PO4 Vs HCl:

(1) TITRATION OF Na2CO3 Vs HCl:

ILLUSTRATIVE EXAMPLE:
The following volume of 0.1M HCl Solution is added to the in20 ml 0.1M Na2CO3 Solution the pH of resulting solution in each case.
(H2CO3, Ka1= 4×10-6, Ka2= 5×10-11)
(1) 0.0 ml (No HCl added)
(2) 10 ml HCl is added
(3) 20 ml HCl is added
(4) 30 ml HCl is added
(5) 40 ml HCl is added 
                                                            

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