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Oxidation & Activity Series

  1. Jun 30, 2015 #1
    According to my chemistry textbook, Cu will not be oxidized by Pb(NO3)2, for Cu is lower on the activity series relative to Pb; Cu will not react with Pb(NO3)2.

    Why is that? Copper should still be able to oxidize regardless of its position on the activity series. So, why does its position on the activity series matter? Why doesn't this happen?

    Cu (s) + Pb(NO3)2 (aq) ----> Cu(NO3)2 (aq) + Pb (s)
     
  2. jcsd
  3. Jul 1, 2015 #2

    Borek

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    Staff: Mentor

    So if the position on the activity series doesn't matter, what is the activity series for?
     
  4. Jul 1, 2015 #3
    Thank you Borek for replying.

    I think the activity series simply list the willingness of certain elements to become oxidized (lose electrons): Those on the top are more willing to oxidize than those on the bottom.

    What I do not understand is why Cu wouldn't react with Pb(NO3)2. Wouldn't Cu simply transfer two of its electrons to Pb, become positively charged, and form an ionic bond with NO3)2, resulting in Cu(NO3)2? Why would it being lower on the activity series than Pb prevent this from happening is my question.

    Is it because the electrons always move from the more willing element to the less willing element without exception? That is the only explanation I can think of.
     
  5. Jul 1, 2015 #4

    Borek

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    That's the correct way of understanding the activity series. Actually the simplest way of producing the simplest form of the activity series is by putting a piece of one metal into the solution of ions of another metal. Put a piece of iron into the copper solution, copper deposits on the iron surface. Put a piece of copper in the solution of Fe2+, nothing happens. Which is more active? Exactly the same will happen when you do the test with lead and copper.

    When you get deeper into these things you will learn reality is sometimes more complicated, but as rule of thumb activity series serves its purpose quite well.
     
  6. Jul 2, 2015 #5
    So, in some ways, the activity series is similar to heat flow: Heat flows from a hotter object to a colder object; electrons migrate from a more willing/better conductor to a less willing/poorer conductor. And if one wanted to reverse this flow/movement of electrons, work would have to be done.
     
  7. Jul 2, 2015 #6

    Borek

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    I am not sure I like this analogy, but it is not entirely incorrect :wink:

    Definitely chemical reactivity has nothing to do with how good a conductor metal is. Al is highly active, Ag is quite noble, both are good conductors, with many much worse conductors in between.
     
  8. Jul 2, 2015 #7
    Also, Borek, are the two metals really not interacting?

    Suppose copper metal is placed in a solution of ionic lead (Pb2+ (aq)). Then, according to what you said, nothing should happen, because Pb is more active than Cu.

    However, I imagine that the electrons do momentarily transfer from Cu to Pb. It is just that, since Pb is more active, it transfers the electrons right away back to Cu. So, the net effect would appear to be that the two metals do not react/interact with each other.
     
  9. Jul 2, 2015 #8

    Borek

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    There are equilibrium concentrations of both ions that can be calculated using Nernst equation. You will probably learn about it later.
     
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