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Pka and solubility

by accarter15
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accarter15
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Oct5-05, 12:56 AM
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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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Borek
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Oct5-05, 05:18 PM
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Quote Quote by accarter15
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.




GCT
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Oct6-05, 05:35 PM
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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.

GCT
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Oct7-05, 12:05 PM
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Pka and solubility

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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