Analyze the Data 2-2: Effects of Strong Bases on pH

Effects of Strong Bases on pH The graph to the right illustrates the effect that the addition of a strong base such as sodium hydroxide has on the pH of an aqueous 0.1 M solution of an amino acid. Assume that prior to the addition of any OH, the entire dissolved amino acid sample is in its fully protonated form. The addition of OH causes the expected steep increase in solution pH until, between roughly 0.03 and 0.07 M NaOH, the solution pH remains almost constant at a pH of approximately 1.8.

What causes the resistance to change in pH in this range? What are solutions that resist changes in pH called? What organic chemical group on the amino acid is most likely responsible for this phenomenon at pH 1.8? Additional base causes the pH to again increase rapidly until the base concentration reaches 0.15 M and 0.25 M, at which points the solution pH hovers around values of 6 and 9.3, respectively. What is the significance of these pH values? Which amino acid do you suspect is being titrated?

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