Chapter 1: Electro Chemistry Lesson 1

Electro Chemistry (Lesson 1)

Ion-electron equation:

Rules

1.      Balance any other element except for oxygen and hydrogen.

2.      To balance oxygen atoms add water molecules to the side deficient.

3.      To balance hydrogen atoms add hydrogen to the side deficient.

4.      Balance the charge by using electrons.

5.      Balance the no. of electrons

6.      Cancel the electrons

e.g.

MnO₄^- +Fe²⁺ = Mn²⁺ + Fe³⁺

Step 1:

Fe²⁺=Fe³⁺ + 1e^- 

Step 2:

MnO₄^- + 8H⁺=Mn²⁺ + 4H₂O

Step 3:

MnO₄^- + 8H⁺ +5e^- = Mn²⁺ + 4H₂O

Step 4:

5x(Fe²⁺=Fe³⁺ + 1e^- )

MnO₄^- + 8H⁺ +5e^- =  Mn²⁺ + 4H₂O

Step 5:

MnO₄^- + 5Fe²⁺ + 8H⁺ = Fe³⁺ + Mn²⁺ +4H₂O

Note:

·         The above reaction is a redo reaction because oxidation and reduction take place simultaneously.

·         Mangnate (VII) ions are oxidizing agents while Iron (II) ions are reducing agents.

·         Species which can attract electrons from another species are oxidizing agents. Oxidizing agents are always reduced.

·         Species which can give electrons to another species are called reducing agents.

Balance the ion electron equations below?

1) Cr₂O₇^2- + I^- = I₂ + Cr³⁺

2) Cr₂O₇^2- + Fe²⁺= Fe³⁺ + Cr³⁺