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Electrochemical cells: What happenswhen twodifferent metals arekept inasinglesolution watch

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    What are the reactions that occur when two different metals are kept in a single solution of salt of another metal?
    For example, copper and zinc rod connected by a high resistance voltmeter and half submerged in sodium chloride solution, what are the reactions occurring when the zinc rod begins to dissolve?
    I am asking this because in half cell reactions there is always the metal and its cation in solution, so the Cu2+ ions can be reduced and Zn atoms can be oxidised. But I cannot figure out the reactions that will occur when there is no cu2+ ions or Zn2+ ions in the solution, it is apparent that the Zn atoms are oxidised to zinc ions but what is reduced here? Thanks for reading.

    Ref: Lasanga cell in wiki, galvanic corrosion (though it involves oxygen it seems)
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    (Original post by ssadi)
    What are the reactions that occur when two different metals are kept in a single solution of salt of another metal?
    For example, copper and zinc rod connected by a high resistance voltmeter and half submerged in sodium chloride solution, what are the reactions occurring when the zinc rod begins to dissolve?
    I am asking this because in half cell reactions there is always the metal and its cation in solution, so the Cu2+ ions can be reduced and Zn atoms can be oxidised. But I cannot figure out the reactions that will occur when there is no cu2+ ions or Zn2+ ions in the solution, it is apparent that the Zn atoms are oxidised to zinc ions but what is reduced here? Thanks for reading.

    Ref: Lasanga cell in wiki, galvanic corrosion (though it involves oxygen it seems)
    If you stick a piece of copper and a piece of zinc into an orange you can record a potential difference between the copper and zinc via an external circuit. The orange contains acid and hence hydrogen ions.

    The solution of sodium chloride in your example contains hydrogen ions, which are far enough below the electrode potential of zinc (-0.76V) to continue the reaction:

    2H+ + 2e --> H2(g)

    I imagine that the build up of hydroxide ion excess changes the relative electrode potentials and stops the reaction after a short while. However, I've never tried it.

    Let's not forget that there is a tendency of electrons to flow from a reactive metal to a less reactive metal WITHOUT chemical processes being involved. This is the science behind a thermocouple. The relative potential changes with temperature allowing the temperature to be calculated and displayed.
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    (Original post by charco)
    If you stick a piece of copper and a piece of zinc into an orange you can record a potential difference between the copper and zinc via an external circuit. The orange contains acid and hence hydrogen ions.

    The solution of sodium chloride in your example contains hydrogen ions, which are far enough below the electrode potential of zinc (-0.76V) to continue the reaction:

    2H+ + 2e --> H2(g)

    I imagine that the build up of hydroxide ion excess changes the relative electrode potentials and stops the reaction after a short while. However, I've never tried it.

    Let's not forget that there is a tendency of electrons to flow from a reactive metal to a less reactive metal WITHOUT chemical processes being involved. This is the science behind a thermocouple. The relative potential changes with temperature allowing the temperature to be calculated and displayed.
    Thanks
 
 
 
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