A 1.00-L aqueous solution is prepared by adding 0.0500 mol of hypochlorous acid, HOCl
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A 1.00-L aqueous solution is prepared by adding 0.0500 mol of hypochlorous acid, HOCl, and 0.0500 mol of cyanide ion, CN−, at 25 °C. Relevant equilibrium data are provided.
• Ka(HOCl) = 3.5×10−8
• Kb(CN−) = 1.6×10−5
• Kw = 1.0×10−14 at 25 °C
Assume volumes are additive and activity coefficients are unity.
(a) Write the net ionic equation describing the reaction that takes place after the two solutions are combined.
(b) Calculate the numerical value of the equilibrium constant, K, for the reaction written in part (a) at 25 °C.
(c) Construct an equilibrium-concentration table for the reaction in part (a), starting with the initial 0.0500 M concentrations of each reactant. Define x clearly, and express equilibrium concentrations in terms of x.
(d) Determine the equilibrium value of x and use it to calculate the pH of the final solution at 25 °C. Report the pH to two decimal places.
(e) Justify whether it is reasonable to neglect any reverse hydrolysis reactions of the conjugate species when performing the calculation in part (d).