100 mL of a 0.1M solution of the tetrapeptide Trp-Arg-Phe-Glu is adjusted to pH = 2.1. The solution is then titrated with 0.1M NaOH to a final pH of 12.5. Sketch the titration curve, labeling the pH and volume axes. Indicate clearly the volume of NaOH needed to reach each relevant pKa value, the isoelectric point (pI) and equivalence point(s). Relevant pKa values are: 2.1, 4.2, 9.5 and 12.5.