Electrochemical series and its uses

Electrochemical Series

• list of elements


• arranged in increasing order of their standard reduction potential values


• also known as activity series

Li    K    Ba    Ca    Na    Mg    Al    Zn    Cr    Fe    Sb    Pb    H₂    Cu    Fe    Ag    Au    F₂

Uses of Electrochemical Series

1. To compare the oxidizing and reducing strengths.
   
   Example:
   Cu⁺⁺ + 2e^-  ----->  Cu    E⁰ = + 0.34
   Zn⁺⁺ + 2e^-  ----->  Zn    E⁰ = - 0.76
   
   Since the E⁰ value of Cu⁺⁺ is greater and can be easily reduced. Therefore, Cu⁺⁺ is a stronger oxidizing agent the Zn⁺⁺. In the electrochemical series, F₂ is the strongest oxidizing agent and Li⁺ is the weakest oxidizing agent.
   
   
   


2. Construction of Galvanic cell.
   
   The electrode for a galvanic cell are chosen referencing the electrochemical series. Anode has lower reduction potential and cathode has higher reduction potential.
   
   
   


3. Calculation of Emf of the cell.
   
   The galvanic cell has two half cells: anode and cathode half cells.
   Emf is the difference of the standard reduction potential of the cathode to anode.
   Thus, E⁰_(cell) = E⁰_red(cathode)  -  E⁰_red(anode)
   
   
   


4. Prediction of the spontaneity of a reaction.
   
   When emf of cell based on a specific redox reaction is calculated, if the emf is +ve, the reaction is spontaneous.
   
   Zn/Zn⁺⁺ // Cu⁺⁺/Cu
   
   E⁰_(cell) = E⁰_Zn/Zn++  -  E⁰_Cu++/Cu  = 0.34V - ( - 0.76V ) = + 1.1V
   
   So, the reaction is spontaneous.
   
   
   


5. To predict whether the atom liberates hydrogen form acid or not.
   
   The metal having a high tendency to lose e^- can displace H⁺ ion form acid.
   This means metal with low reduction potential can liberate hydrogen ion.
   Li⁺ can liberate more H⁺ ion than Na⁺.
   
   
   


6. To predict the relative reactivity of metals.
   
   Reduction potential ↑  ------> tendency to loose elcetrons ↓  ------> reactivity ↓