A chemist prepares three separate aqueous solutions of triethylamine
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A chemist prepares three separate aqueous solutions of triethylamine, a weak base, at 25 °C. The initial molarities of the base are 0.10 M, 0.010 M, and 0.0010 M, respectively. The base-ionization constant of triethylamine at this temperature is Kb=5.2×10−4.
(a) Explain, without performing detailed numerical calculations, how the percent ionization of triethylamine is expected to change as the initial concentration decreases across the three solutions.
(b) Rank the three solutions from highest to lowest pH and justify your ranking with reference to relevant equilibrium relationships.
(c) For the 0.0010 M solution, describe qualitatively how the validity of any small-change approximation used in a quantitative pH calculation would differ from its validity in the 0.10 M solution, and explain your reasoning.