Why is Acetic acid (pKa = 4.76) stronger than carbonic acid (pKa = 6.36)?












2












$begingroup$


In order to try and understand this, I evaluated it via stability of conjugate bases. The acetate vs carbonate ion. The only difference is what's attached to the carboxyl group, the $ce{-CH3}$ and the $ce{-OH}$. Both anions seem to have equal resonance structures as I think resonance mainly only happens on the carboxyl group.



I think that because the methyl group is just larger than the hydroxyl group, it is able to better stabilize the negative charge on the molecule overall. But I also remember hearing that carbon can have a positive inductive effect, meaning it pushes electron density toward the carboxyl group, which would make it less stable.



I originally thought that carbonate would be more stable because the oxygen would pull the electron density toward itself, making the charge more evenly distributed.



If somebody could explain with diagrams I would appreciate it. I lost access to my software that did electron modeling functions for me.






organic-chemistry stability







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  • 5




    $begingroup$
    Possible duplicate of Why is carbonic acid a weaker acid than acetic acid?
    $endgroup$
    – Mithoron
    6 hours ago
















2












$begingroup$


In order to try and understand this, I evaluated it via stability of conjugate bases. The acetate vs carbonate ion. The only difference is what's attached to the carboxyl group, the $ce{-CH3}$ and the $ce{-OH}$. Both anions seem to have equal resonance structures as I think resonance mainly only happens on the carboxyl group.



I think that because the methyl group is just larger than the hydroxyl group, it is able to better stabilize the negative charge on the molecule overall. But I also remember hearing that carbon can have a positive inductive effect, meaning it pushes electron density toward the carboxyl group, which would make it less stable.



I originally thought that carbonate would be more stable because the oxygen would pull the electron density toward itself, making the charge more evenly distributed.



If somebody could explain with diagrams I would appreciate it. I lost access to my software that did electron modeling functions for me.






organic-chemistry stability







share|improve this question









New contributor




Abdullah Afridi is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$








  • 5




    $begingroup$
    Possible duplicate of Why is carbonic acid a weaker acid than acetic acid?
    $endgroup$
    – Mithoron
    6 hours ago














2












2








2





$begingroup$


In order to try and understand this, I evaluated it via stability of conjugate bases. The acetate vs carbonate ion. The only difference is what's attached to the carboxyl group, the $ce{-CH3}$ and the $ce{-OH}$. Both anions seem to have equal resonance structures as I think resonance mainly only happens on the carboxyl group.



I think that because the methyl group is just larger than the hydroxyl group, it is able to better stabilize the negative charge on the molecule overall. But I also remember hearing that carbon can have a positive inductive effect, meaning it pushes electron density toward the carboxyl group, which would make it less stable.



I originally thought that carbonate would be more stable because the oxygen would pull the electron density toward itself, making the charge more evenly distributed.



If somebody could explain with diagrams I would appreciate it. I lost access to my software that did electron modeling functions for me.






organic-chemistry stability







share|improve this question









New contributor




Abdullah Afridi is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$




In order to try and understand this, I evaluated it via stability of conjugate bases. The acetate vs carbonate ion. The only difference is what's attached to the carboxyl group, the $ce{-CH3}$ and the $ce{-OH}$. Both anions seem to have equal resonance structures as I think resonance mainly only happens on the carboxyl group.



I think that because the methyl group is just larger than the hydroxyl group, it is able to better stabilize the negative charge on the molecule overall. But I also remember hearing that carbon can have a positive inductive effect, meaning it pushes electron density toward the carboxyl group, which would make it less stable.



I originally thought that carbonate would be more stable because the oxygen would pull the electron density toward itself, making the charge more evenly distributed.



If somebody could explain with diagrams I would appreciate it. I lost access to my software that did electron modeling functions for me.






organic-chemistry stability




organic-chemistry stability






share|improve this question









New contributor




Abdullah Afridi is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|improve this question









New contributor




Abdullah Afridi is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|improve this question




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edited 4 hours ago









Night Writer

1,432218




1,432218






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asked 7 hours ago









Abdullah AfridiAbdullah Afridi

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Abdullah Afridi is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






Abdullah Afridi is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.








  • 5




    $begingroup$
    Possible duplicate of Why is carbonic acid a weaker acid than acetic acid?
    $endgroup$
    – Mithoron
    6 hours ago














  • 5




    $begingroup$
    Possible duplicate of Why is carbonic acid a weaker acid than acetic acid?
    $endgroup$
    – Mithoron
    6 hours ago








5




5




$begingroup$
Possible duplicate of Why is carbonic acid a weaker acid than acetic acid?
$endgroup$
– Mithoron
6 hours ago




$begingroup$
Possible duplicate of Why is carbonic acid a weaker acid than acetic acid?
$endgroup$
– Mithoron
6 hours ago










1 Answer
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$begingroup$

Well actually the $mathrm{pK}_mathrm{a1}$ for carbonic acid at 25 °C is 3.6. The pka = 6.36 is also including the equilibrium with dissolved $ce{CO2}$ in aqueous solution.






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    1 Answer
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    1 Answer
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    $begingroup$

    Well actually the $mathrm{pK}_mathrm{a1}$ for carbonic acid at 25 °C is 3.6. The pka = 6.36 is also including the equilibrium with dissolved $ce{CO2}$ in aqueous solution.






    share|improve this answer









    $endgroup$


















      4












      $begingroup$

      Well actually the $mathrm{pK}_mathrm{a1}$ for carbonic acid at 25 °C is 3.6. The pka = 6.36 is also including the equilibrium with dissolved $ce{CO2}$ in aqueous solution.






      share|improve this answer









      $endgroup$
















        4












        4








        4





        $begingroup$

        Well actually the $mathrm{pK}_mathrm{a1}$ for carbonic acid at 25 °C is 3.6. The pka = 6.36 is also including the equilibrium with dissolved $ce{CO2}$ in aqueous solution.






        share|improve this answer









        $endgroup$



        Well actually the $mathrm{pK}_mathrm{a1}$ for carbonic acid at 25 °C is 3.6. The pka = 6.36 is also including the equilibrium with dissolved $ce{CO2}$ in aqueous solution.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 7 hours ago









        MaxWMaxW

        14.8k12158




        14.8k12158






















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