Balancing redox reactions
This presentation is the property of its rightful owner.
Sponsored Links
1 / 14

Balancing redox reactions 2 PowerPoint PPT Presentation


  • 115 Views
  • Uploaded on
  • Presentation posted in: General

Balancing redox reactions 2. Two methods for balancing redox reactions: Oxidation number method Half-reaction method. Balance redox equations using the oxidation number method. Balance redox equations in acidic and basic solutions using the half reaction method.

Download Presentation

Balancing redox reactions 2

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Balancing redox reactions 2

Balancing redox reactions 2


Balancing redox reactions 2

Two methods for balancing redox reactions:

Oxidation number method

Half-reaction method.

  • Balance redox equations using the oxidation

  • number method.

  • Balance redox equations in acidic and basic

  • solutions using the half reaction method.


Balancing redox reactions 2

Half-reactions show the oxidation or reduction reaction separated.

+1

+2

0

0

Cu(s) + 2 AgNO3(aq) → Cu(NO3)2(aq) + 2 Ag(s)

Oxidation:Cu → Cu2+ + 2e–

Reduction:Ag+ + 1e– → Ag

Half reactions are often shown as aqueous net ionic equations – spectator IONS not included.


Balancing redox reactions 2

  • Redox reactions usually require an acidic or basic solution.

  • Acid / base not oxidized or reduced in reaction.

  • Usually converted to water.

  • Half-reaction method is used for balancing redox reactions in the presence of acid or base.


Balancing redox reactions 2

Balancing Redox Reactions in Acidic Solutions

-2

+6

-2

+4

+3

-2

+6

Cr2O72–(aq) + SO32–(aq) → Cr3+(aq) + SO42–(aq)

1: Assign ox.numbers and write half-reactions.

Oxidation:SO32- → SO42- + 2e–

Reduction:Cr2O72- + 3e– → Cr3+

Not ionic (no spectators) –keep together!


Balancing redox reactions 2

2: Balance all elements except H and O.

Oxidation:SO32- → SO42- + 2e–

Reduction:Cr2O72- + 6e– → Cr3+

2

3: Balance oxygen atoms by using H2O.

Oxidation:SO32- + H2O → SO42- + 2e–

Reduction:Cr2O72- + 6e– → 2 Cr3+ + 7 H2O


Balancing redox reactions 2

4: Balance hydrogen atoms using H+ions.

Oxidation: SO32- + H2O → SO42- + 2e–

+2 H+

Reduction: Cr2O72- + 6e– → 2 Cr3+ + 7 H2O

14 H+ +

5: Balance the number of electrons lost and gained.

Oxidation: 3 x (SO32- + H2O → SO42- + 2e– +2 H+)

3 SO32- + 3 H2O → 3 SO42- + 6e– +6 H+

Reduction: 14 H+ + Cr2O72- + 6e– → 2 Cr3+ + 7 H2O


Balancing redox reactions 2

6: Add the two half-reactions.

Oxidation: 3 SO32- + 3 H2O → 3 SO42- + 6e– +6 H+

Reduction: 14 H+ + Cr2O72- + 6e– → 2 Cr3+ + 7 H2O

8 H+ + Cr2O72- + 3 SO32- → 2 Cr3+ + 3 SO42- + 4 H2O


Balancing redox reactions 2

Balance the following reaction in a acidic solution.

-1

+7

0

+4

MnO4– + I– → MnO2 + I2

3 x ()

2

Oxidation: I1- → I2 + 2e–

2x ( )

4 H+ +

Reduction: MnO41- + 3e– → MnO2

+ 2 H2O

Oxidation: 6 I1- → 3 I2 + 6e–

Reduction: 8 H+ + 2 MnO41- + 6e– → 2 MnO2 + 4 H2O

8 H+ + 2 MnO4– + 6 I– → 2 MnO2 + 3 I2 + 4 H2O


Balancing redox reactions 2

Balancing Redox Reactions in Basic Solutions

  • For basic solutions add hydroxide ions.

+3

+4

+4

+7

MnO4– + C2O42– → CO2 + MnO2

2

Oxidation: C2O42- → CO2 + 2e–

4 H+ +

+ 2 H2O

Reduction: MnO41- + 3e– → MnO2

*5a: Add the same number of OH- as H+ to BOTH sides of the equation.


Balancing redox reactions 2

Oxidation C2O42- → 2 CO2 + 2e–

4 H2O

2

Reduction:4 H+ + MnO41- + 3e– → MnO2 + 2 H2O

4 OH- +

+ 4 OH-

5b: Eliminate H+ / OH- by forming water..

Cancel any waters you can to simplify each half reaction.

OxidationC2O42- → 2 CO2 + 2e–

3 x ()

2x ( )

Reduction:2 H2O + MnO41- + 3e– → MnO2 + 4 OH-


Balancing redox reactions 2

Oxidation3 C2O42- → 6 CO2 + 6e–

Reduction:4 H2O + 2 MnO41- + 6e– → 2 MnO2 + 8 OH-

4 H2O + 2 MnO4– + 3 C2O42– → 2 MnO2 + 6 CO2 + 8 OH–


Balancing redox reactions 2

Balance the following reaction in a basic solution.

+1

+1

+3

-1

N2O + ClO– → NO2– + Cl–

3 H2O +

2

Oxidation: N2O → NO2- + 4e–

+ 6 H+

2 H+ +

+ 1 H2O

Reduction: ClO- + 2e– → Cl-

5a: Add same number of OH- to BOTH side.

5b:Cancel any waters you can to simplify half reactions.


Balancing redox reactions 2

6 H2O

3

Oxidation: N2O → NO2- + 4e–

6 OH- +

3 H2O +

2

+ 6 OH-

+ 6 H+

Reduction: ClO- + 2e– → Cl-

+ 2 OH-

2 OH- +

+ 1 H2O

2 H+ +

2 H2O

1

2

1

Oxidation: N2O → NO2- + 4e–

6 OH- +

2

+ 3 H2O

Reduction: ClO- + 2e– → Cl-

2x ( )

+ 2 OH-

1 H2O +

2 H2O + 2 ClO- + 4e– → 2 Cl- +4 OH-

2 OH– + 2 ClO– + N2O → 2 Cl– + 2 NO2– + H2O


  • Login