Determine the Eo for a Cu-Pb Voltaic Cell

1. Obtain and wear goggles.
2. Use a 24-well test plate as your voltaic cell. Use Beral pipets to transfer small amounts of 0.10 M Cu(NO3)2 and 0.10 M Pb(NO3)2 solution to two neighboring wells in the test plate. CAUTION: Handle these solutions with care. Clean up spills as directed.
3. Obtain one Cu and one Pb metal strip to act as electrodes. Polish each strip with steel wool. Place the Cu strip in the well of Cu(NO3)2 solution and place the Pb strip in the well of Pb(NO)3 solution. These are the half cells of your Cu-Pb voltaic cell.
4. Make a salt bridge by soaking a short length of string in a beaker than contains a small amount of 1 M KNO3 solution. Connect the Cu and Pb half cells with the string.

The standard cell potential (E₀) for a Cu-Pb voltaic cell is +0.215V

The experiment is used to determine the standard electrode potential of the Cu-Pb Voltaic cell.

Explanation:

A Voltaic cell is one in which electric energy is produced as a result of the difference in electric potential between two electrodes in chemical solutions that are usually connected by a salt bridge.  

In a voltaic cell, the anode electrode is where oxidation (loss of electrons) occurs while reduction (gain of electrons) occurs at the cathode electrode.

The standard cell potential (E₀) is the difference between the potential of the cathode and anode at standard conditions, that is, at standard temperature, pressure and concentration.  

It is usually expressed as

E₀ = E₀cell (cathode) - E₀cell (anode)

From the given question, the half cell equations are :

Cu(s) - 2e ⇒ Cu²⁺. with  oxidation reaction occuring at the anode  

Pb²⁺  + 2e ⇒ Pb (s).  with reduction reaction occuring at the cathode

Meaning that the solid copper electrode is oxidised by losing two electrons which are gained by the Pb²⁺ ions which are subsequently reduced to solid lead at the other electrode.  

Each half cell reaction has a standard electric potential  (recall that the standard electric potential is the potential at standard conditions, that is, at standard temperature, pressure and concentrations.

)

The overall voltaic cell equation is given as:

Cu(s) I Cu²⁺(aq) II Pb²⁺ (aq) I Pb(s)

The standard cell potential E₀ is obtained by

:

E₀ = E₀cell (cathode) - E₀cell (anode)

At standard conditions, E₀ (Cu(s) ⇒ Cu²⁺  + 2e)  = - 0.340V

                       E₀ (Pb²⁺ + 2e ⇒ Pb(s) = - 0.125V

Therefore, the standard cell potential for a Cu-Pb voltaic cell is,

E₀ = -0.125V - (-0.340V)

  = -0.125V + 0.340V

  = +0.215V

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