Consider the zwitterion of the amino acid alanine, which is the predominant form of the acid at neutral pH. Draw its structural formula. Imagine that the pH of a solution of alanine is gradually lowered until the zwitterion picks up a proton. Draw the structural formula of the resulting ion. Write the chemical equation for this addition of a proton. Note that the equilibrium constant for the opposite reaction is Ka. The pKa value for this is 2.3. Use the Henderson-Hasselbalch equation to obtain the ratio of the different ionic forms of alanine in the solution at a pH of 4.0. Which form predominates at this pH?