Module 8   Part H: Redox Equations    10 points

Balance the following redox equations written in net ionic form:

Acid Media: 10 points

1.    C2O4 2- (aq)      +     MnO4 1- (aq)    + H 1+ (aq)    Mn 2+ (aq)  +    CO2 (g)   +   HOH (l)

Half equation:        MnO4 1-             à       Mn 2+                                                       1. Balance Mn

MnO4 1-             à       Mn 2+        +      4 H2O               2. Balance O

8 H 1+    +     MnO4 1-             à       Mn 2+        +      4 H2O               3. Balance H

4. Charge Balance:

+8   -1    =   +2    + 0

+7    =   +2

-5    +7    =   +2

Gain 5 electrons :

5 e1-   +    8 H 1+      +     MnO4 1-               à       Mn 2+        +      4H2O

This is the Reduction Step

5. Make e1- Gain = e1- Loss:

2 Reductions = 5 Oxidations

(5 e1-   +   8 H 1+    +   MnO4 1-             à       Mn 2+        +      4H2O) x 2

10 e1-   +  16 H 1+  +   2 MnO4 1-             à    2 Mn 2+        +    8H2O

Half equation:

C2O4 2-   à  2 CO2                                                        1. Balance C

2. Balance O   Oxygens are balanced

3. Balance H    Hydrogens are balanced

4. Charge Balance:

-2   =   0

-2   =   0     -2

Loss 2 electrons :

C2O4 2-   à  2 CO2    +      2 e1-

This is the Oxidation Step

5. Make e1- Gain = e1- Loss:

2 Reductions = 5 Oxidations

( C2O4 2-   à  2 CO2    +      2 e1- ) x 5

5 C2O4 2-   à  10 CO2    +     10 e1-

Substitute half equations into net ion equation to balance

5 C2O4 2-   à  10 CO2    +     10 e1-

10 e1-   +  16 H 1+  +   2 MnO4 1-      à    2 Mn 2+        +    8H2O

--------------------------------------------------------------------

5 C2O4 2--   +   2  MnO4 1-   + 16 H 1+  à    2 Mn 2+     +   5 CO2     +  8 HOH

Basic Media (10 point Bonus)

2.  Bi2O3 (s)   + OH 1- (aq) + OCl 1- (aq) →   BiO3 1- (aq)    + Cl 1- (aq)    +   HOH (l)

1st half equation:

Bi2O3          à     2  BiO3 1-                            1. Balance Bi

3  OH 1-     +      Bi2O3          à     2  BiO3 1-                            2. Balance O (add OH1-)

3. Balance H (add OH1- and H2O)

3  OH 1-      +         3  OH 1-      +          Bi2O3          à     2  BiO3 1-  +  3 HOH

6  OH 1-         +          Bi2O3          à     2  BiO3 1-  +  3 HOH

4. Charge Balance:

-6   + 0    =   -2    +   0

-6    =   -2

-6    =   -2    +  -4

Loss 4 electrons:

6  OH 1-     +      Bi2O3          à     2  BiO3 1-  +  3 HOH  + 4 e1-

This is the Oxidation Step

5. Make e1- Gain = e1- Loss:

2 Reductions (2 e1 Gained) = 1 Oxidation (4 e1 Lost)

(6  OH 1-     +      Bi2O3          à     2  BiO3 1-  +  3 HOH  + 4 e1-) x 1

6  OH 1-     +      Bi2O3          à     2  BiO3 1-  +  3 HOH  + 4 e1-

2nd half equation:

OCl 1-    à      Cl 1-                                                      1. Balance Cl (Cl is balanced)

OCl 1-    à      Cl 1-     +      1  OH 1-            2. Balance O (add OH1-)

3. Balance H (add H2O and OH1-)

1 HOH    +     OCl 1-    à      Cl 1-     +      1  OH 1-+      1  OH 1-

1 HOH    +     OCl 1-    à      Cl 1-     +      2  OH 1-

4. Charge Balance:

+0   -1    =   -1    - 2

-1    =   -3

-2    -1    =   -3

Gain 2 electrons :

2 e1-   +    1 HOH    +     OCl 1-    à      Cl 1-     +      2  OH 1-

This is the Reduction Step

5. Make e1- Gain = e1- Loss:

2 Reductions (2 e1 Gained) = 1 Oxidation (4 e1 Lost)

(      2 e1-   +    1 HOH    +     OCl 1-    à      Cl 1-     +      2  OH 1-  ) 2

4 e1-   +    2 HOH    +    2 OCl 1-    à    2  Cl 1-     +      4  OH 1-

Substitute half equations into net ion equation to balance

4 e1-   +    2 HOH    +    2 OCl 1-    à    2  Cl 1-     +      4  OH 1-

6  OH 1-     +      Bi2O3          à     2  BiO3 1-  +  3 HOH   +    4 e1-

--------------------------------------------------------------------------------

1  Bi2O3 (s)   + 2 OH 1- (aq) +  2 OCl 1- (aq) →  2 BiO3 1- (aq)  +  2 Cl 1- (aq)    +  1 HOH (l)

Zn      +       NO3 1-   +     H 1+      à   Zn 2+    +   NH4 1+     +    H2O

MnO4 1-   +   C2O4 2-  +   H 1+      à    Mn 2+   +   CO2         +    H2O

Cr2O7 2-   +   C2H5OH  +   H 1+   à    Cr 3+   +   HC2H3O 2     +    H2O

SO4 2-     +     CH2O     +   H 1+     à    H2S     +   CO2         +    H2O

FeS   +       NO3 1-   +     H 1+        à   NO   +   Fe 2+    +   SO4 2-     +    H2O

Cr2O7 2-   +   Cl 1-   +     H 1+        à   Cr 3+   +   Cl2     +    H2O

H2O2   +   MnO4 1-   +     H 1+        à   Mn 2+   +   O2         +    H2O

Cr 3+         +       ClO3 1-   +     OH 1-      à   CrO4 2-  +   Cl 1-     +    H2O

Mn 2-        +        Br2          +   OH 1-      à    MnO2   +   Br 1-     +    H2O

Fe(OH)2    +       O2         +    H2O         à    Fe 3+       +   OH 1-

Zn              +     NO3 1-     +    OH 1-      à    ZnO2 2-  +     NH3     +   H2O

AsO2 1-       +    ClO 1-      à    AsO3 1-   +    Cl 1-     (basic solution)

MnO4 1-     +     C2O4 2-    +    OH 1-     +  H2O   à     MnO2    +    CO3 2-

N2H4         +    O2           à     N2          +   H2O2      (basic solution)