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Off Topic Chemistry Problem

Discussion in 'Pre-Medical - MD' started by justin342, Feb 13, 2002.

  1. justin342

    justin342 Member

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    I know this is off topic, but I didn't have anywhere else to turn for help and I know there are a lot of smart people in here.

    Explain why a mixture of HCl and KCl does not function as a buffer, where as a mixture of HC(2)H(3)O(2) and NaC(2)H(3)O(2) does.

    Anyone?
     
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  3. imtiaz

    imtiaz i cant translate stupid
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    HCl and KCl fully dissociate in solution, they are ionic compounds. Acetic acid and sodium acetate are covalent compounds which partially ionize and thus can become protonated/deprotonated as required to maintain pH (up to an extent).

    HCl is a strong acid, acetic acid is a weak acid.
     
  4. justin342

    justin342 Member

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    Sounds good. It seems obvious now that I read it. Thanks for the help.
     
  5. souljah1

    souljah1 Attending

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    I'd like to add that HCl and KCl do not provide us with any base what soever. Acetic acid is a weak acid which can dissociate and associate based on its chemical structure (henderson hasselback or however you spell it).
     
  6. daisygirl

    daisygirl woof

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    Actually HCl and KCl do provide bases; the Cl- anions are considered lewis bases.
     
  7. souljah1

    souljah1 Attending

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    the question i have is: will the pH go up if you add Cl-? I know that Cl- is a lewis base, but does Cl- have the capability of buffering??? it has no conjugate really.
     
  8. daisygirl

    daisygirl woof

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    </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by souljah1:
    <strong>the question i have is: will the pH go up if you add Cl-? I know that Cl- is a lewis base, but does Cl- have the capability of buffering??? it has no conjugate really.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You need a weak acid and its conjugate salt or a weak base and its conjugage salt in order to have a buffer solution. As imtiaz stated HCl and KCl will dissociate 100%, thus no buffer solution. The only reason I pointed out that Cl- is a lewis base is because there is a base present. In the question presented Cl- does not have the capability of buffering b/c it is not going to shift the equilibrium over to the left, thus the buffering effect. Adding more Cl- will increase the pH.
     
  9. mongoose

    mongoose Banned
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    Ultimately, there is no buffer effect because the Cl- anion is very stable and will not attack water or anything else to gain a proton. Well, there may be some things it will attack, but they would be few and far between, maybe I- anion but not to any great extent. To get a buffer, you must have something capable of attacking and removing protons from other species. Typically, this will involve an oxygen with a negative charge or a nitrogen with it's lone pair of electrons.
     

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