Pka and solubility

  • Thread starter accarter15
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The pKa of p-nitrophenol is 7.15. Would you expect it to dissolve in sodium bicarbonate solution? The pKa of 2,5-dinitrophenol is 5.15. Will it dissolve in bicarbonate solution. Pka of bicarbonate solution is 6.34. Any help will be greatly appreciated, thanks.
 

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  • #2
Borek
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accarter15 said:
Pka of bicarbonate solution is 6.34.
That was pH I suppose?

Both substances will dissolve if converted to ions. Use Henderson-Hasselbalch equation to calculate how much of the substance will be in the ionic form.
 
  • #3
GCT
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at equal concentrations of p-nitrophenol and its conjugate base, the solution will be basic, since pKa=pH at equal concentrations. This means that the molecule has basic characteristics (the alcohol motif), assuming that p-nitrophenol is insoluble in pure water, than in an acidic solution of bicarbonate.......think about the common ion effect. You should apply the same reasoning with your other compound.
 
  • #4
GCT
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ok, I went off on a tangent there, you simply need to compare the pKas, in a mixture of bicarbonate and either of the two compounds, which would be the weaker acid, thus the stronger base?

For instance, p-nitrophenol has a higher pKa, thus would it be more acidic than bicarbonate? If not, than bicarbonate would dissolve the compound in an aqueous solution.
 

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