Final answer:
In the physiological pH range of around 7.4, a fatty acid exists as an anion. This is due to the carboxyl group donating a hydrogen ion, leaving the fatty acid in a negatively charged state.
Step-by-step explanation:
In the physiological pH range, which is around 7.4, a fatty acid exists typically in its anion form. This is because the carboxyl group (-COOH) present in fatty acids can donate a hydrogen ion (H+) in the physiological pH environment, becoming a negatively charged carboxylate anion (-COO−). Since the carboxyl group makes the molecule more hydrophilic, fatty acids are found in biological structures like phospholipids and triglycerides, where they play vital roles in membrane structure and energy storage, respectively.
It is worth noting that under physiological conditions, the conjugate acid forms of amines, i.e., ammonium ions, have pKa values of 9 to 11, meaning that in a physiological medium, amines exist as ammonium ions. Similarly, phosphoric acids lose a proton and exist as phosphate anions under these conditions.