PbO2

Discussion in 'Feedback and Suggestions' started by seba, Aug 31, 2008.

  1. seba

    Thread Starter Guest

    Here: http://www.allaboutcircuits.com/vol_1/chpt_11/1.html

    It says that PbO2 is "Lead Peroxide" (Peroxide is R1-O-O-R2), which would mean that the structure is somewhat like

    / Pb \
    O - O

    and assumes that Pb is in (II), 2+ state... where in fact the structure is O = Pb = O, which means the Pb is in (IV), 4+ state... so this is "Lead(IV) oxide" or "Lead dioxide" so naming it Lead Peroxide is incorrect: there is no peroxide group in it.

    Thou the validity of this could be of course argued (a lot of people actually use this name and similar less correct names - lead superoxide, see http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=49854910&loc=ec_rcs) we can't overlook the definition of peroxide as "A peroxide is a compound containing an oxygen-oxygen single bond." (source: wikipedia). So saying Lead(IV) oxide or Lead dioxide is in all ways more acceptable.
     
  2. jpanhalt

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    Jan 18, 2008
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    Not sure of the exact question. True, PbO2 can be written two ways. In batteries, it is Pb(IV). I wish those who write the equations for lead-acid batteries would include the electrons, not just the protons. This link, page 24, does that, and I think it gives a better picture of what's happening.

    John
     
  3. Dave

    Retired Moderator

    Nov 17, 2003
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    Thanks for the feedback.

    Please forgive my ignorance, I am not a chemist, but is the query basically that the information as written in the above AAC section is incorrect as written?

    If so, I will seek advice from someone who is in the know to clarify what is being written in the OP. I am certainly not the person to pass comment.

    Dave
     
  4. jpanhalt

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    Dave,

    I responded to the poster without reading the section in AAC. Big mistake on my part. In retrospect, it appears the poster was pointing out an error in AAC without using that word. I thought he was just discussing the slight ambiguity of writing PbO2 instead of Pb(IV)O2.

    If it is OK with you, I will take a closer look at the section tomorrow or Wednesday and send you a draft from a chemist's viewpoint. Today is a big holiday in the US.

    John
     
  5. Dave

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    That would be great John, I appreciate your input. Thanks.

    Enjoy your holiday.

    Dave
     
  6. seba

    Thread Starter Guest

    Actually i was pointing out that the name "Lead peroxide" is wrong and "Lead dioxide" or "Lead(IV) oxide" should be used instead.

    Lead peroxide and Lead dioxide both have the same written molecular formula but different structure.
    Compare the true Lead peroxide (http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=22169324&loc=ec_rcs) vs. Lead dioxide (http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=14793&loc=ec_rcs).

    An analogy would be the more known isomerism in organic chemistry, for example C2H6O "means" both the well known ethanol and dimethylether as well as some other compounds.

    So my point, the molecular formula (PbO2) is written correct but the name used Lead peroxide is wrong, although it is used incorrectly in some other non-chemistry literature.

    In other words just replace the words "Lead peroxide" with "Lead dioxide"/"Lead(IV) oxide", as no peroxides are formed.
     
  7. jpanhalt

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    My revision will include the oxidation states to avoid such ambiguities. I need to research a bit more on the currently accepted nomenclature. There is lots of ambiguity, including patents with the USPTO and "approved" MSDS's. On reading the whole section, starting with chemistry, I don't think a simple word substitution will work.

    My suggestions for revision are just in rough draft now. I think to understand what is happening, the concepts of oxidation and reduction need to be introduced. Then, go to the bit about electron flow and batteries, and finally the lead-acid battery. My working outline for lead-acid batteries has three sections: currently accepted model; sulfation; and gassing. I will try to keep it short, perhaps a little over simplified, but accurate. After all, the "C" is AAC is not for chemistry.

    John
     
  8. Dave

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    Thanks John, please check your e-mails.

    Dave
     
  9. Dave

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    seba,

    jpanhalt has worked through the current section of the e-book which is being discussed here and has made several corrections to the text (see the attached .DOC file).

    Can I ask that you read through jpanhalts corrections and make comments on the modifications, in-line with your original query? I can convert the file to PDF if you cannot read .DOC files.

    Hopefully we can reach some consensus on the text and add the corrections to the e-book.

    Thanks.

    Dave
     
  10. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
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    I can find no reference to lead peroxide in any chemistry reference, not even in old 1960's CRC Handbook of Chemistry and Physics. I will assume the the lead peroxide terminology used in storage battery articles is outdated. Pb(IV)O2 is lead dioxide.

    Reference the AAC Chapter ed.doc for the following quote from said DOC file
    The 2.2 V in the text is incorrect. It should be about 2.0 V, I will take the suggested 2.04 V unless I find a slightly contradictory answer. It does vary with temperature. Although you can measure a considerable higher voltage immediately after charging, (maybe as high as the incorrect number) this is not a valid reading. The battery must be heavily loaded for a few minutes to dissipate this "surface effect". Then the open circuit battery will give a valid reading.

    I am not able to verify the use of the bisulfate ion HSO4- in the suggested changes to the equations for the images in the DOC file. By verify, I do not see the bisulfate in my references, but do see the sulfate ion.I will re work the equations as suggested, only using the sulfate ion SO4-- in place of bisulfate HSO4- . This applies to both the discharge and charge equations.

    Otherwise, I agree with the suggested changes, and will try to get them entered.

    Thanks for the work.

    Dennis Crunkilton
     
  11. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
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    Attached are the equation images: discharge 00259.png, 00393.png .
     
  12. jpanhalt

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    That nomenclature was explained in the footnote I provided. Unfortunately, the term,"lead peroxide," is still used in industry. It is, of course, Pb(IV)dioxide.

    Electrochemist's use 2.04 V.



    Be sure to keep track of the protons. I personally prefer the bisulfate as being a little more accurate. My reference to bisulfate is based on a Department of Energy (USA) monograph on lead-acid batteries. I provided the reference in the materials I submitted and would be happy to send you a electronic version.

    From basic chemistry, the second ionization constant of sulfuric is fairly low and is approximately 0.01 mol/L (see: http://cat.inist.fr/?aModele=afficheN&cpsidt=3438107). It is often simpler to consider pKa's when discussing acids. The corresponding pKa is thus approximately 2, which means that at the pH in a fully charged battery (given in Wikipedia as 0.5) almost all of the sulfur is present as bisulfate, not fully ionized to sulfate.

    John

    Edit: If you go with sulfate, the two negatives are usually written one above the other. If that cannot be done, the "-2" might be clearer. The first time I saw the "--", I thought it was a dash.
     
    Last edited: Oct 19, 2008
  13. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
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    What I really meant to say is that I agree with you that Lead peroxide is incorrect. It will be changed in the text per your corrections.

    While I cannot accomodate foot notes, I can put your foot note in a frame in Latex-PDF/table in html, and reference it that way. Text update is over a week away.
    Then it will be 2.04 V.


    The link was dead, all the way up to the root web site earlier today. I will try it again when I am back in a week. If I cannot get it,I will ask for your electronic version.

    I think what I am hearing is that at the concentration of actual battery acid, the ionization is as bisulfate. And that the bisulfate equations are more accurate for that reason. Having agreed with you on the bisulfate, I feel that I still need to retain the old sulfate equations because they are so widely used-- or misused.

    However, that should not stop us from also showing the more correct bisulfate equations if identified as such. With the more correct bisulfate equations, I think that I can dumb down the old ionized sulfate equations to a form I saw in a battery article which shows H2SO4 with no ionization at all. Less confusing for non-chemists. I think I can get away with that If I also have the accurate bisulfate equations.

    [
    I will go with the -2 superscript

    I will check back in a week.
     
  14. jpanhalt

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    Here's another link to the DOE document:

    http://www.hss.energy.gov/NuclearSafety/techstds/standard/hdbk1084/hdbk1084.pdf

    The formula is on pdf page 24; document page 13. I also noted that Wikipedia under electrochemistry uses the bisulfate form:

    http://en.wikipedia.org/wiki/Lead_acid_battery

    Finally, the JOM article (http://www.tms.org/pubs/journals/JOM/0101/Nelson-0101.html ) initially uses just the sulfate form, but later on page 4 of 13, it shows the bisulfate equation.

    The choice of sulfate vs. bisulfate in the equation is relatively unimportant; although, the bisulfate is more accurate for the form in solution. I consider the more important change is to include the oxidation state changes that the lead undergoes and to show the electrons. The original version did not show the electrons, so one was left having to know that when Pb went to Pb(II), two electrons were released.

    "-2" is fine. A superscript "=" would also probably work.

    I checked these links, and they all work for me this morning.

    John
     
  15. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
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    Thanks John,

    for the update to the lead-acid chemistry. The suggested changes have been entered in the master copy at ibiblio.org . You have been given credit as John Panhalt. If this iscorrect let us know. Also, let us know if I have let any erros creep into the copy at ibiblio.

    Thanks again,

    Dennis Crunkilton