An aqueous mixture is prepared by dissolving the following substances in enough water…
CHEMISTRY · Multi-part · AP · Chemistry · Acids and Bases · Acids and Bases
Problem
An aqueous mixture is prepared by dissolving the following substances in enough water to make exactly 1.00 L of solution at 25 °C.
• 0.100 mol of hydrofluoric acid, HF (Ka=6.8×10−4)
• 0.100 mol of ammonia, NH3 (Kb=1.8×10−5)
• 0.050 mol of ammonium chloride, NH4Cl (a strong electrolyte)
Assume ideal solution behavior and take Kw=1.0×10−14 at 25 °C.
(a) Write the net ionic equation that best represents the principal reaction occurring in this solution.
(b) Calculate the equilibrium constant, K, for the reaction written in part (a).
(c) Taking into account all species initially present, set up—but do not yet solve—an algebraic representation for the equilibrium concentrations of all acidic and basic species in terms of a single variable. Clearly indicate how the presence of NH4+ from NH4Cl affects your expressions.
(d) Solve for the equilibrium concentration of hydronium ion and determine the pH of the solution at 25 °C, reporting your answer to two decimal places.
(e) Evaluate whether the common-ion effect introduced by NH4+ significantly shifts the pH compared with a similar mixture lacking NH4Cl. Support your conclusion with quantitative or qualitative reasoning.