Final answer:
The fraction of the carboxyl group present as COO- depends on the pH of the solution and the pKa of the carboxylic acid, with deprotonation being favored at pH values above the pKa.
Step-by-step explanation:
To determine the fraction of the carboxyl group present as COO- (the deprotonated form), we need to consider the pKa of the carboxylic acid and the pH of the environment. Carboxylic acids typically have pKa values ranging from about 4 to 5. When the pH of the solution is greater than the pKa, the acid will donate a proton and exist predominantly in its deprotonated form, COO-. Conversely, at a pH lower than the pKa, the carboxylic acid will mostly be in its protonated form, COOH.
The Henderson-Hasselbalch equation can help estimate the ratio of deprotonated to protonated forms at a given pH. However, without specific pH and pKa values, a definitive fraction cannot be provided. Usually, at physiological pH (approximately 7.4), most carboxylic acids would be in the COO- form due to the pH being higher than their pKa values.