A monoprotic weak acid,

CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases

Problem

A monoprotic weak acid, HB(aq)\text{HB}(aq), is placed in water at an initial concentration of 0.100 M. Its dissociation at 25 °C is represented by HB(aq)⇌H+(aq)+B−(aq)\text{HB}(aq) \rightleftharpoons \text{H}^+(aq) + \text{B}^-(aq) The acid-dissociation constant is Ka=1.8×10−5K_a = 1.8 \times 10^{-5} at this temperature. (a) Let xx denote the equilibrium concentration of H+(aq)\text{H}^+(aq) generated by dissociation. Using this definition, write expressions for the equilibrium concentrations of all species present and set up the KaK_a equation in terms of xx. (b) Solve the equation obtained in part (a) without making a simplifying assumption, and report the numerical values of the equilibrium concentrations of HB\text{HB}, H+\text{H}^+, and B−\text{B}^-. Show all steps and retain correct significant figures. (c) Determine the percent ionization of the acid under these conditions and discuss briefly how the magnitude of the percent ionization relates to the strength of the acid.

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