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?

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

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