A solution containing 0.139 mmol of the triprotic acid tris(2-aminoethyl)amine ∙ 3HCl plus 0.115 mmol HCl in 40 mL of 0.10 M KCl was titrated with 0.490 5 M NaOH to measure acid dissociation constants.

(a) Write expressions for the experimental mean fraction of protonation, n̅_H(measured), and the theoretical mean fraction of protonation, n̅_H(theoretical).

(b) From the following data, prepare a graph of n̅_H(measured) versus n̅_H. Find the best values of pK₁, pK₂, pK₃, and pK'_w by minimizing the sum of the squares of the residuals, Σ[n̅_H (measured) – n̅_H(theoretical)]².

(c) Create a fractional composition graph showing the fractions of H₃A³⁺, H₂A²⁺, HA⁺, and A as a function of pH.

Transcribed Image Text:

N(CH,CH,NH )3 3CI Tris(2-aminoethyl)amine · 3HCI H3A³* · 3CI