OKSIDLANISH-QAYTARILISH REAKSIYALARINING TURLARI

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   Oksidlanish –qaytarilish reaksiyalari 4 ga bo’linadi:

         1)molekulararo  oksidlanish-qaytarilish reasiyalari;

         2) ichki molekulayr oksidlanish-qaytarilish reaksiyalari;

         3) disproporsiyalanish reaksiyalari;

         4) murakkab oksidlanish-qaytarilish reaksiyalari.

         Molekulararo oksidlanish-qaytarilish reaksiyalarida oksidlovchi va qaytaruvchi turli molekulalarda bo’ladi.

                        _{0             +6             +2             +4}

                    Cu + 2H₂SO₄= CuSO₄+SO₂  + 2H₂O           

                    Cu⁰    -2       ®Cu⁺²           2        1

                          S⁺⁶  -2 e      ®  S⁺⁴           2       1

 

                          CuSO₄+Zn=ZnSO₄+Cu

 

                        Zn⁰     -2e     →    Zn⁺²       2        1

                        Cu⁺²   +2e     ®    Cu⁰           2        1

Molekulalararo oksidlanish –qaytarilish reaksiyalari gazlar orasida:

 

                              3H₂+N₂=2NH₃

                  4NH₃+5O₂=4NO+6H₂O                                                                                                                                    

                               2SO₂+O₂=2SO₃

           Qattiq moddalar orasida:

                             2Mg(q)+O₂(g)=2MgO(q)

                             2Sb(q)+3CI₂(g)=2SbCI₃(q)

               Qattiq moddalar bilan suyuqliklar orasida:

                                      4HCI(S)+MnO₂(q)=CI₂(g)+ Mn CI₂(s)+2H₂O(s)

                 16HCI(s)+2KMnO₄(q)=5CI₂(g)+2MnCI₂(s)+8H₂O(s)+2KCI(s)

                    Qattiq moddalar orasida:

                         2AI(q)+ Fe₂O₃(q)=AI₂O₃(q)+2Fe(q)

                    C(q)+2PbO(q)= 2Pb(q)+CO₂(g) 

             Aksariyat oksidlanish-qaytarilish reaksiyalari eritmada ketadi:

            3Na₃AsO₃+K₂Cr₂O₇+4H₂SO₄= 3Na₃AsO₄+Cr₂(SO₄)₃+4H₂O+K₂SO₄

                       2NaCrO₂+3H₂O₂+2NaOH=2Na₂CrO₄+4H₂O

                Bunday reaksiyalar qatoriga oksidlanish darajasi turlicha bo’lgan lekin bir xil atomlardan iborat moddalar orasidagi reaksiyalarni ham olish mimkin:

                                         2H₂S+H₂SO₃=3S+3H₂O

                           5HCI+HCIO₃=3CI₂+3H₂O

      Disproporsiyalanish yoki o’z-o’zidan oksidlanish –qaytarilish reaksiyalari

         Molekula tarkibidagi bir xil element atomoning  oksidlanish darajasi ham ortadi, ham kamayadi:

                               3K₂MnO₄+2H₂O=2KMnO₄+MnO₂+4KOH

                   3KCIO=2KCI+KCIO₃

                   3HNO₂=HNO3+2NO+H₂O

                  Na₂SO₃=3Na₂SO₄+Na₂S

                 6NaOH+3S=2Na₂S+Na₂SO₃+3H₂O

                2KOH+CI₂=KCI+KOCI+H₂O

                6KOH+3CI₂→5KCI+KCIO₃+3H₂O

              Ichki molekulyar-oksidlanish qaytailish  reaksiyalarida oksidlovchi va qaytaruvchi

          Bitta molekulani o’zida lekin har xil  element atomlari ba’zan bir xil element    

          atomlari ham bo’lishi mumkin:

                                      2KNO₃=2 KNO₂+ O₂

                                      4HNO₃=4NO₂+2H₂O+O₂

                                                           2 Ba(NO₃)₂=2BaO+4NO₂+O2

                                        (NH₄)₂Cr₂O₇=Cr₂O₃+N₂+H₂O

                                         2HgO= 2Hg+O₂

                                        2KClO₃=2KCl+3O₂

                  Murakkab oksidlanish-qaytarilish reaksiyalarida ikkitadan ortiq elementlarning oksidlanish darajasi o’zgaradi. 

       As₂S₃ ga konsentrlangan   HNO₃  ta’sirida  quyidagi reaksiya sodir bo’ladi :

3Аs₂S₃+28HNO₃+4H₂O→6H₃AsO₄+9H₂SO₄+28NO

                                        _{+3                                         +5}              

                                 2 As        -4e        ®2As                   3

                                   3S^-2      -24e      ®  3S⁺⁶                   

                                    N⁺⁵    -3e        ®N⁺²                      28

 

                        3As₂S₃+28НNO₃+4H₂O=6Н₃АsO₄+9H₂SO₄+28NO

               Elektron balans usuli maktab dasturi bo’yicha to’la o’rgailganligi uchun faqat  yarim reaksiyalar usuli (ion –elektron usulga to’xtalamiz. Bu usulning afzalligi shuki buna asosan suvdagi eritmalar olinadi. Elektron balans usulidan farq qilib  oxirgi holatda haqiqiy  mavjud ionlar qo’llaniladi.Elektron balans usulida esa  faraz   qilinadigan ionlar ishlatiladi,chunki eritmada  Mn⁺⁷, Cr⁺⁶, S⁺⁶,N⁺⁵,N^-3, Cl⁺⁷ va bohqa  ionlar mutlaqo uchramaydi. Ayni paytda  eritmada haqiqiy bor bo’lgan ionlar Mn²⁺, Cr³⁺,MnO₄^-,CO₃^2-, ClO₄^-,Cr₂O₇^2-, SO₄^2- va boshqalar hisoblanadi.Yarim reaksiyalar usulida atomlarning oksidlanish darajasini bilish shart emas va reaksiya  mahsulotlarini ham reaksiyani tenglashtirih jarayonida chiqarish mumkin.

               Yarim reaksiyalar usulida oksidlanish –qaytarilish tenglashtirishda

      quyidagilarni hisobga olish kerak.

            Bunda oksidlovchi va qaytaruvchi hamda ularning reaksiya mahsulotlari ion  holda yozilib  ular asosida yarim reaksiyalar tuziladi.Kuchli elektrolitlar ion holda yozilib , kuchsiz elektrolitlar molekulyar  holda(cho’kma, gaz) yoziladi.Reaksiya    mahsulotlarini yozishda  1 tablisa asos qilib olinadi:

 

   2-jadval

      Eng ko’p qo’llaniladigan qaytaruvchi va oksidlovchilar va ularning reaksiya

     mahsulotlari                                                                                                        

        

 

Oksidlovchlar

Qaytaruvchilar

                                              Galogenlar va ularning birikmalari 

 

                          Cl₂→HCl                                  HJ→J₂

                           Br₂→HBr                                 HBr→Br₂

                            J₂ →HJ                                   HCl→Cl₂

                        HClO→HCl

                       KClO₃→KCl

                                         

Oltingugurtning birikmalari

                     H₂SO₄ →   H₂S                             H₂S →S             

                     H₂SO₄ →  S                             Na₂SO₃→ H₂SO₄

                      Na₂SO₃→S                                        S→SO₂

                                           Azotning birikmalari

                     HNO₃→NO₂                               NH₃→N₂

                     HNO₃→NO₂                            KNO₂  →KNO₃

 

 

 

                      HNO₃→NO

 

 

1

2

                                 HNO₃→  N₂O                         N₂  → NH₃

     

                                 KNO₂  →  NO

                            (кislotali sharoitda )

                                                   Marganes birikmalari          

                            KMnO₄→MnSO₄                  MnSO₄  →MnO₂   

                   (kislotali sharoitda suyultir.  H₂SO₄)                                        

                          KMnO₄→MnO₂

                 (neytral sharoitda Н₂О )

                        MnO₂→ K₂MnO₄

                (кuchli ishqoriy sharoitda)

                      MnO₂→ MnSO₄

               (кislotali sharoitda suyultirilgan  H₂SO₄)

                                                    Xromning birikmalari

                K₂Cr₂O₇→Cr₂(SO₄)₃                        CrCI₃  →     K₂CrO₄

             (кislotali sharaoitda H₂SO₄)

                                                 Qo’rg’shin birikmalari

                   PbO₂  →  Pb(NO₃)₂

                 (кislotali sharoitda HNO₃)

                                                  Qalay birikmalari

                  SnCI₄→ SnCI₂                              SnCI₂ → SnCI₄        

                                                                  

                                                  Temir birikmalari

 

                 FeCl₃→ FeCl₂                             FeCl₂→ FeCl₃

 

                                          Mishyak birikmalari

                                                                AS₂S₃ → H₃AsO₄+H₂SO₄

                                                               AS₂S₅ → H₃AsO₄+H₂SO₄

 

                  

 Yarim reaksiyalar usulida oksidlanish –qaytarilish reaksiyalarini         tenglashtirish uchun jadval ma’lumotlari asosida(2 jadval) yoki moddalarning     oksidlanish-qaytarilish xossalarini bilgan holda  oksidlanish yoki qaytarilish   mahsulotlari topiladi. Bunda oksidlovchi va qaytaruvchi uchun 4 ta qoidadan     foydalaniladi:

1)    Kislotali muhitda oksidlovchi tarkibidagi ortiqcha kislorod vodorod ioni bilan bog’lanib suv molekulasini hosil qiladi va qaytariladi.

                                    ₊ 

                                      О+2Н+2 e     ®   Н₂О

                                   _{-         +                        2+} 

                         MnO₄+8H+5e® Mn     +       4H₂O 

              2) Neytral va ishqoriy sharoitda oksidlovchi tarkibidagi ortiqcha kislorod suv  molekulasi bilan bog’lanib gidroksid ionini hosil qiladi va qaytariladi

  

                                   O    +H₂O   +2e   ®2OH

                                     _{-                                                             -}

                           MnO₄+2H₂O+3e=MnO₂+4OH

               3)  kislotali va neytral sharoitda qaytaruvchi tarkibidagi yetishmayotgan kislorod     suvdan olib vodorod ionini hosil qiladi.

                                                               ₊          

                       H₂O   -   2e   ®    O  +2H

                          _{2-                                                       2-         +}

                     SO₃      +   H₂O  -2e   ®SO₄+2H

           

4)Kuchli ishqoriy muhitda qaytaruvchi yetishmayotgan kislorodni gidroksid ionidan olib oksidlanadi va suv hosil qiladi.                  _-          

                       2OH    -2e    ® O   +   H₂O

                             _{2-             -                                    2-}

                       SO₃+2OH   -  2e   ®  SO₄+H2O

                           _{-                    -                                 -}

                        J  +  6OH    -6e   ®  JO₃  +   3H₂O

                Misol 1.

                         KNO₂+KMnO₄+H₂SO₄=KNO₃+K₂SO₄+2H₂O

              Reaksiya paytida eritmani  pushti rangi o’zgarib rangsizlanadi. Yarim reaksiya   usulini ishlatish uchun reaksiyada qatnashgan ionlarni alohida ko’chirib yoziladi.

                          _{-                   -       +                         -                 2+}          

                    NO₂+MnO₄+H     ®  NO₃+    Mn+ …..

              Oksidlovchining qaytarilgan va qaytaruvchining oksidlangan mahsulotlarini   ko’rsatuvchi yarim reaksiyalar tuziladi.                                                                      

                                                                                       ₂₊

                            MnO₄ ^-    ®           Mn           (1)

                                 _{-                                 -} 

                            NO₂        ®       NO₃            (2)

                 (1) yarim reaksiyaga 1 qoidani (2) yarim reaksiyaga (3) qoidani qo’llaymiz.

                                        _{-                    +                              2+}      

                               MnO₄   +    8H +5e  ®   Mn   +   4H₂O      2

                                                          _{-                                                           -                     +}

                               NO₂    +     H₂O  -2e®  NO₃   +    2H         5

                 Bu reaksiyalardagi strelkalarni tenglik ishorasiga aylantirish uchun  o’ng va     chap  tomondagi zaryadlar sonini tenglashtirish kerak. 

                                 _{-        +                  2+}

                         MnO₄+H+5e=Mn+4H₂O

                                _{-                                 -              +}

                         NO₂+H₂O-2e=NO₂+2H

 

                 Umumiy reaksiyani tuzish uchun oksidlovchi qabul qilgan va qaytaruvchi yo’qotgan elektronlar sonidan foydalanib va eng kichik ko’paytuvchiga ko’paytirib hadma had qo’shamiz.

                                                               _{-                                           -            +}

                               NO₂+H₂O -2e=NO₃+2H              5

                                                          _{-          +                  2+}                

                               MnO₄+8H+5e=Mn+4H₂O           2

                                             _{-                                     -           +                -            +            2+}

                    5NO₂+5H₂O+2MnO₄+16H=5NO₂+10H+2Mn+8H₂O

         O’xshash ionlarni qisqartirib reaksiyaning ion tengalamasini hosil qilamiz.

                          _{-                      -          +              -              2+}    

                  5NO₂+2MnO₄+6H=5NO₂+2Mn+3H₂O

                 Ion tenglamadan molekular tenglamaga o’tish uchun ion tenglamaning chap    va o’ng tomoniga  mos keladogan anion va kationlarni qo’shamiz, shundan so’ng   ionlarni molekulalarga birlashtirib molekular tenglamani hosil qilamiz.

                     _{-                        -              +                  -               2+}  

              5NO₂+ 2MnO₄+  6H=  5NO₂  +2Mn  + 2H₂O

                    _{+                    +                 2-             +                        2-              +            2-}

               +5K       2K+   3SO₄     5K         2SO₄+    2K  SO₄

 

                  5KNO₂+2KMnO₄+3H₂SO₄=5KNO₃+2MnSO₄+K₂SO₄+3H₂O

                 Oxirgi tenglama oksidlanish-qaytarilish reaksiyasining to’liq molekular

     tenglamasi hisoblanadi.

                   Misol 2.

                          _{+7                   +4                                        +2                        +6}

                   2KMnO₄+5K₂SO₃+3H₂SO₄=2MnSO₄+6K₂SO₄+3H₂O

                   

                       Mn⁺⁷   +5e             ®Mn⁺²          2

                       

                        S⁺⁴      +2e          ®S⁺⁶                5

                    Yarim reaksiya usulida  tenglashtirilsa:

                2KMnO₄+3Na₂SO₃+H₂O=3Na₂SO₄+2MnO₂+2KOH

                                       _{-                2-                                                 2-}

                                MnO₄+   SO₃+H₂O→MnO₂+ SO₄+……

         Oksidlovchi uchun (2) qoidani va qaytaruvchi uchun (3) qoidani qo’llab yarim    reaksiyalarni yozamiz:

                       _{-                                      -}

                MnO₄+2H₂O+3e=MnO₂+4OH              2

                     _{2-                                    2-         +}

              SO₃+H₂O-2e=SO₄+2H                          3

 

                      _{-            2-                                                2-               -}

        2MnO₄+3SO₃+H₂O=2MnO₂+SO₄+2OH

         To’liq molekulyar tenglama yozish uchun mos ionlar qo’shiladi.

                     2KMnO₄+3Na₂SO₃+H₂O=3Na₂SO₄+2MnO₂+2KOH

            Vodorod peroksidi oksidlanish-qaytarilish reaksiyalarida  sharoitga qarab ham  oksidlovchi ham qaytaruvchi xossasini namoyon etadi. Kuchli qaytaruvchilar bilan  vodorod peroksidi oksidlovchi va reaksiya muhitiga qarab quyidagicha qaytariladi:

1)     kislotali muhitda vodorod peroksidi vodorod ioni bilan bog’lanib suv   

 molekulasini hosil qiladi.

                                     H₂O₂+2H⁺₊2e®2H₂O

2)     neytral va ishqoriy sharoitda vodorod peroksidi o’ziga ikkita elektron qabul qilib  gidroksid ionini hosil qiladi.

                                              _-

                                Н₂О₂+2е   ®2ОН

 

      Misol 3.         Н₂О₂+FeSO₄+H₂SO₄ →Fe₂(SO₄)₃+H₂O

             

                                 Fe²⁺-2e=Fe^{3 +}                         2

                       

                                H₂O₂+2H⁺ + 2e=2H₂O           1

                                2Fe²⁺+H₂O₂+2H⁺=2Fe³⁺+2H₂O

                 Bu reaksiya molekula holda quyidagicha yoziladi:

                         H₂O₂+2FeSO₄+H₂SO₄=Fe₂(SO₄)₃+2H₂O

        Misol 4.                 2KJ+H₂O2  →J₂+2KOH

                     2J ^--2e=J₂             1

                     H₂O₂+2e=2OH^-  1

       Misol 5.      2NaCrO₂+3H₂O₂+2NaOH=2Na₂CrO₄+4H₂O

                                _{-                 -                     2-}             

                     CrO₂+4OH-3e=CrO₄+2H₂O               2

                        H₂O₂+2e=2OH^-                               3

                             _{-               -                                    2-}  

                2CrO₂+2OH+3H₂O₂=2CrO₄+4H₂O

              Vodorod peroksidi kuchli oksidlovchilar bilan (KMnO₄, (NH₄)₂Cr₂O₇,K₂Cr₂O₇    

             va bosqalar)  bilan qaytaruvchi bo’lib reaksiyaga kirishadi va oksidlanadi.

1)     kislotali muhitda vodorod peroksidi o’zidan ikkita elektron berib kislorod   molekulasini hosil qiladi va oksidlanadi.             

                                        Н₂О₂-2е=О₂+2Н^-

      2)ishqoriy sharoitda vodorod peroksidi o’ziga ikkita elektron biriktirib  kislorod va suv molekulasini hosil qiladi.          

                         Н₂О₂+2ОН ^--2е=О₂+2Н₂О+

          Misol   6.               Н₂О₂+МnO₄^-+H⁺→O₂+Mn²⁺…….

                   Н₂О₂-2e=O₂+2H ⁺                              5

                  MnO₄^-+8H⁺+5e=Mn²⁺+4H₂O             2

          5H₂O₂+2MnO₄^-+6H⁺=5O₂+2Mn²⁺+8H₂O

          5H₂O₂+2KMnO₄+3H₂SO₄=5O₂+2MnSO₄+H₂SO4+8H2O  

 

        Misol 7.                 H₂O₂+[Fe(CN) ₆]^3-+OH^-=O₂+[Fe(CN)₆]^4-+………

                      H₂O₂+2OH^--2e=O₂+2H2O                          1

                    [ Fe(CN)₆]^3-+1e=[Fe(CN)₆]^4-                           2

                          H₂O₂+2OH^-+2[Fe(CN)₆] ^3-=O₂+2H₂O+2[Fe(CN)₆]^4-

                          H₂O₂+2K₃[Fe(CN)₆]+2KOH=O₂+2K₄[Fe(CN)₆]+2H₂O