Dissotsiatsiya qaytar jarayondir

ta’siri.

117. Gidroliz darajasi va konstantasi.  Gidroliz reaksiyasi  qaytar bo’lganligi uchun unda muvozanat qaror topadi. Muvozanatga massalar ta’siri qonunini tatbiq etamiz.

     Masalan: kuchsiz kislota va kuchli asosdan hosil bulgan tuz

       CH₃ COO^-  + H₂O = CH₃ COOH + OH ^– 

      

        [CH₃COOH]_*[OH^-]                                         [CH₃COOH]_*[OH^-]

 K= ---------------------------;          K_g=K_*[H₂O]= ---------------------------

        [CH₃COO^-]_*[H₂O]                                               [CH₃COO^-]

 

Shu tenglamani surat  va maxrajini [H⁺] ga ko’paytirsak:

                             [CH₃COOH]_*[OH^-]_*[H⁺]      [OH^-]_*[H⁺]

                     K_g=---------------------------   =      --------------

                                 [CH₃COO^-]_*[H⁺]                   K_kis

 

[OH^-]_*[H⁺]=K_w  qiymat suvning ion kopaytmasi ekanligi hisobga olinsa

                                    K_w

                    K_g=---------------------

                                    K_kis

   Agar                     NH₄Cl+H₂O=NH₄OH+HCl

                                NH₄⁺ + H₂O  =  NH₄OH  +H ⁺

                                [ NH₄OH]*[H ⁺]

                 K_g=     --------------------  

                                 [ NH₄⁺] 

 

    Bu tenglamani ham surat  va maxraji [OH^-] ga ko’paytirilsa, unda

                            

                                [ NH₄OH]_*[H ⁺]_*[OH^-]       [H ⁺]_*[OH^-]

                 K_g=     ----------------------------     =  --------------

                               [ NH₄⁺]_*[OH^-]                        K _asos

 

                                                K_w

                                K_g=  ---------------;

                                               K _asos

       Tuzning gidroliz  konstantasi asos yoki kislotaning dissotsiyalanish konstantasi qancha  kichik bolsa yuqori bo’ladi.

       Agar tuz kuchsiz asos va kuchsiz kislotadan tashkil topgan bo’lsa  gidroliz konstantasi

          CH₃COO ^-  + NH₄⁺  + H₂O = CH₃COOH + NH₄OH

                            [ CH₃COOH] _* [ NH₄OH]

                  K_g=---------------------------------- ;

                              [ CH₃COO ^-]_*[ NH₄⁺] 

      Agar bu tenglama [H⁺]_*[OH^-] ga ko’paytirilsa:

                                               

                          [ CH₃COOH] _*[ NH₄OH]* [H⁺]_*[OH^-]        [H⁺]_*[OH^-]

                  K_g=-------------------------------------------------= ------------------

                              [ CH₃COO ^-]_*[ NH₄⁺] [H⁺]_*[OH^-]            K_kis*K_asos

 

                                                [H⁺]_*[OH^-]              K_w

                                      K_g=------------------= ------------

                                                 K_kis*K_asos            K_kis*K_asos                                                     

                                                K_w

                               K_g=-------------------

                                              K_kis*K_asos

 

             Bu tenglamaga ko’ra kislota va asosnong dissotsilanish konstantasi qancha  kichik bo’lsa uning gidrolizlanish konstantasi shuncha yuqori bo’ladi.

                            Gidrolizlanish darajasi

     Kuchli asos va kuchsiz kislotadan hosil bo’lgan tuzlarnong gidrolizini ko’raylik.

                   CH₃COONa  +H₂O =  CH₃COOH + NaOH

                    CH₃COO^- +    +H₂O =  CH₃COOH + OH^-

                     ( 1-b)_*C                              bC               bC

                               [ CH₃COOH]  [OH^-]        bCbC             b²C 

                    K_g=-----------------------------= --------------=----------

                                  [CH₃COO^-]                    ( 1-b)_*C      ( 1-b)

 

                                     b²C                                                                        K_g

                          K_g=--------------;            1  -  b  =  1     K_g= b²C  ;  b²=-------- 

                                    ( 1-b)                                                                      C

 

                   Demak,   gidroliz darajasi kuchli asos va kuchsiz kislotadan hosil bo’lgan tuzning  konsentrasiyasi qancha kichik bo’lsa gidroliz darajasi yuqori bo’ladi.   

                       NH₄Cl+H₂O= NH₄OH + HCl 

                        NH₄⁺   +H₂O  =   NH₄OH + H⁺ 

                       (1- b)C                     bC        bC

 

                   [NH₄OH] _*[ H⁺]        bC   bC              b²C²            b²C    

         K_g= -------------------  = ---------------=  -------------= --------------

                     [NH₄⁺]                                (1- b)C             (1- b)C         (1- b)    

 

                                  b²C                                                                K_g

                     K_g=------------------;       (1- b) =1 ;      b²C =K_{g ;}  b²=-----        

                                 (1- b)                                                              C

               Kuchsiz asos bilan kuchli kislotadan iborat bo’lgan tuzlar uchun   gidroliz darajasi  tuzning konsentrasiyasiga  teskari bog’langan. Eritma qancha suyultirilgan bo’lsa gidroliz  shuncha tez boradi.

              Agar asetat ammoniyning gidrolizlanishi hisobga olinsa , CH₃COONH₄

Bu modda ham anion va ham kation bo’yicha gidrolizga uchraydi:

         CH₃COONH₄  +  H₂O =  CH₃COOH  +  NH₄OH

         CH₃COO^- + NH₄⁺ + H₂O =  CH₃COOH +  NH₄OH

                b C          bC                     (1-  b)_*C      (1- b )_*C

                                                    Kw           (1-  b)_*C_* (1- b )_*C       ( 1-b)²

                                        Kg= -----------= --------------------------=    -------

                                                  K_as*K_kis          b C_*  bC                       b²

 

                                                  ( 1-b)²               ( 1-b)²            Kw   

                                        Kg= -----------;         ----------= ---------

                                                    b²                       b²            K_as*K_kis

 

     Demak, gidroliz darajasi kuchsiz asos va kuchsiz kislota uchun  eritma konsentrasiyasiga bog’liq emas.

      Gidroliz jarayoni  farmasiyada katta ahamiyatga ega. Ko’pgina dori moddalari eritmada tayyorlanadi.Masalan. yiringli yaralarni tuzatish uchun Pb(NO₃)₂ ishlatiladi. Bu tuz gidrolizlanishi tufayli PbOHNO₃ hosil bo’lib asosiy ta’sir etuvchi modda ana shu hisoblanadi.