The conjugate acid of the hydrogencarbonate ion is carbonic acid, with a pKa of 6.35…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
The conjugate acid of the hydrogencarbonate ion is carbonic acid, with a pKa of . For the reaction of an acid HA with hydrogencarbonate, . Find for phenol (), for p-nitrophenol () and for picric acid (). Say which of the three would release carbon dioxide from the solid salt.
Need a reminder? The key ideaShow
For a weak acid HA, and . For HA with a base B: . The share of HA present as the anion is percent.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Carbonic acid has .
Step 1. Phenol. , so . The reaction hardly goes.
Step 2. p-Nitrophenol. , so . The reaction goes only a little.
Step 3. Picric acid. , so . The reaction goes almost to completion.
Check. Only picric acid is stronger than carbonic acid by a large margin. It releases carbon dioxide from sodium hydrogencarbonate. Phenol does not, and p-nitrophenol is borderline.
Answer: , and .
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