Homework Help: Pka and solubility

1. Oct 5, 2005

accarter15

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.

2. Oct 5, 2005

Staff: Mentor

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. Oct 6, 2005

GCT

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. Oct 7, 2005

GCT

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.