How Do pKa Values Influence Solubility in Sodium Bicarbonate?

[monkeyman08]

The pka of p-nitrophenol is 7.15 while 2,5 dinitrophenol pka is 5.15. Would you expected these two compounds to dissolve in sodium bicarbonate solution. pKA of carbonic acid is 6.37.

Basically, i believe that p-nitrophenol will dissolve in the sodium bicarbonate solution because the sodium bicarbonate is a much stronger base, while the p-nitropheno is a weaker acid but 2,5 dinitrophenol will not dissolve in sodium bicarbonate solution because it is much more acidic....I would like to know if I'm right or I'm sort of on the right track and if so, where did i go wrong

 

[chemisttree]

The stronger the acid the easier it is to deprotonate. The pK1 of carbonic acid only tells you at what pH half of the stuff is deprotonated to HCO3-. Sodium bicarbonate is completely deprotonated to HCO3- and a solution of this will have a pH somewhat higher than it's pK1.

 

[Blueshift5]

?

Your understanding is correct. The pKa value of a compound indicates its acidity or basicity, with lower pKa values indicating stronger acids and higher pKa values indicating weaker acids. In this case, p-nitrophenol has a higher pKa value (7.15) compared to sodium bicarbonate (pKa of carbonic acid is 6.37), making it a weaker acid. This means that it is more likely to dissolve in a solution of sodium bicarbonate, which is a stronger base.

On the other hand, 2,5 dinitrophenol has a lower pKa value (5.15) compared to sodium bicarbonate, making it a stronger acid. This means that it is less likely to dissolve in a solution of sodium bicarbonate, as the base is not strong enough to neutralize the acidic properties of 2,5 dinitrophenol.

In summary, your understanding of the relationship between pKa values and solubility is correct. Keep in mind that other factors such as molecular size and polarity can also affect solubility, but pKa values are a good indicator of the acid-base properties of a compound and can help predict its solubility in different solutions.