Question

Describe and explain observed conductivity changes during the titration of your amino acid. Which parameter is more helpful in locating the first and the second equivalence points, the pH or the electrical conductivity? The amino acid is glutamic acid (HGlu) Thank you.

Answer 1

pH parameter is more helpful in locating the first and the second equivalence points

about the amino acid, glutamic acid, with R = C₂H₄COOH

pK_a1 = 3.20 (a-COOH)

pK_a2 = 4,25 (R - COOH)

pK_a3 = 9.67 (a-NH₃⁺)

It will undergo the following series of acid/base reactions:

Notice that at low pH, below pH = 2.0, glutamic acid carries a net positive charge. After the addition of one equivalent of base, the lowest pK_a group will have been deprotonated, giving no net charge on a glutamic acid. The half-way point of this first wave of the titration will be at pH = pK₁ = 3.2 and the pH of the first equivalence point will occur at about pH = (3.2 + 4.25)/2 = 3.7, the average of the first two pk_a's. This is also the isoelectric point of glutamic acid, the pH_I. Addition of more OH^- begins to remove the second acidic proton, from the COOH of the R-group. Shown below is the titration curve forglutamic acid with the strong base, NaOH.