The conjugate acid of an organic base

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

Problem

The conjugate acid of an organic base, denoted

\mathrm{BH^+}

, has a

pK_a

of 10.6 at 37 °C. At this temperature the ionic product of water is

K_w = 2.4\times10^{-14}

. A

0.0500\,\text{M}

aqueous solution of

\mathrm{BH^+}

is prepared and allowed to reach equilibrium. (a) Express the equilibrium constant

K_a

in terms of the given

pK_a

, and calculate the numerical value of

K_a

for

\mathrm{BH^+}

at 37 °C. (b) Write the equilibrium-constant expression for the dissociation of

\mathrm{BH^+}

in water, clearly identifying all species included. (c) Calculate the equilibrium concentrations of

\mathrm{BH^+}

\mathrm{B}

, and

\mathrm{H_3O^+}

in the solution. (d) Determine both the pH and the pOH of the solution at 37 °C. (e) Compute the percent ionization of

\mathrm{BH^+}

and discuss briefly how this value would change if the initial concentration of

\mathrm{BH^+}

were decreased while the temperature remained constant.