Salt Bridge - Practice Questions & MCQ

It maintains electrical neutrality in two compartments by allowing movement of anions towards anodic compartment and cations towards cathodic compartment.

• It is a glass tube having KCl, KNO₃, ammonium nitrate in a gelatin gel or agar-agar past.
• The gelatin gel allows ionic movement through it but prevents any kind of mixing.
• In the case of KCl or ammonium nitrate, the ionic mobility of cation and anion are same.

Function of a Salt Bridge

• A salt bridge acts as an electrical contact between the two half-cells.
• It prevents mechanical flow of solution but it provides free path for the migration of ions to maintain an electric current through the electrolyte solution. It prevents the accumulation of charges.
• A salt bridge helps in maintaining the charge balance in the two half cells.
• A salt bridge minimizes/eliminates the liquid junction potential.
  Liquid Junction Potential: The unequal rates of migration of the cations and anions across a liquid-liquid junction give rise to a potential difference across the junction. This potential difference across the liquid-liquid junction is called liquid junction
  potential.

NOTE: If salt bridge is removed the emf of the cell drops to zero.

• The Daniel cell is a typical galvanic cell. It is designed to make use of the spontaneous redox reaction between zinc and cupric ion to produce an electric current.
• The Daniel cell can be conventionally represented as
  
  
• The Daniel cell reaction is represented as
  
  
• In Daniel cell, electrons flow from zinc electrode to copper electrode through external circuit while metal ions flow form one half cell to the other through salt bridge.
• Here current flows from copper electrode to zinc electrode that is, cathode to anode in external circuit.
• Daniel cell is a reversible cell while a voltaic cell may be reversible or irreversible.
  A voltaic cell is reversible only when it satisfies following conditions:
• The emf of external source is more than that of voltaic cell so that current may flow from external source into the voltaic cell and cell reaction can be reversed.
• If emf of voltaic cell is more than that of external source current flows from voltaic cell into external source.