Electrochemical cells

Take the quiz after reviewing the notes on Electrochemistry
[WATU 2]

Electrochemical cells:

  • When a chemical reaction can produce an electric current we have an electrochemical cell
  • The galvanic cell is an example of an electrochemical cell. Zn is the anode and Cu is the cathode.
  • The chemical reaction in an electrochemical cell is spontaneous reaction or ΔG < 0 or negative
  • The electrode at which oxidation takes place is called the anode
  • The electrode at which reduction takes place is called cathode
  • In an electrochemical cell the anode is at a negative potential (Increased negative charge due to accumulation of electrons M  → Mn+ + ne-¹)
How do you choose the anode and cathode in an electrochemical cell?
  • The anode and the cathode can be determined from the standard electrode potential values for he electrode
  • When comparing the values a larger value for the standard reduction potential indicates that this electrode would undergo reduction in comparison to the electrode having a lower standard reduction potential
How can you verify that the electrodes that you have chosen as anode and cathode are right?
  • You can calculate the E°cell value for the cell  E°cell =  E°cathode –  E°anode
  • If the cell emf obtained is positive the choice of electrodes are right which also implies the reaction is spontaneous ΔG = -ve
  • If the value is negative it represents a non spontaneous reaction, this reaction will not occur or ΔG = +ve or greater than zero.

What is the role of a salt bridge in an electrochemical cell

  • The salt bridge helps in maintaining the electrical neutrality of the solutions in the anodic and cathodic compartments
  • The salt bridge helps in completing the cell circuit
How can you make a salt bridge?
  • A simple form of the salt bridge is a filter paper soaked in KCl
  • The electrolyte should preferably contain a salt of a strong acid and a strong base – the salt should not undergo hydrolysis
  • A glass tube bend twice at 90° or a U shaped glass tube can be used
  • It should be filled with a warm solution of agar in water and KNO3.
  • The contraption should be allowed to cool and you will have a gel in the glass tube which will serve as a source of positive and negative ions
  • Such salt bridges have a life span, once all the ions have been used up they should be replaced
  1. In a Daniel cell, what form does the salt bridge take?
  2. Can you regenerate an electrochemical cell?
  3. Is the galvinic cell a primary or secondary cell?
  4. How can you vary the emf of an electrochemical cell?
  5. What is the effect of temperature on an electrochemical cell?



Electrochemical cells, redox reactions, anode, cathode, positive, negative, oxidation, reduction

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