Chemistry

Problem

For methylamine,

\mathrm{CH_3NH_2}

, dissolved in water at

25\,^{\circ}\mathrm{C}

, which of the following expressions equals the base-dissociation constant

K_b

for the equilibrium

\mathrm{CH_3NH_2 + H_2O \rightleftharpoons CH_3NH_3^+ + OH^-}

? a)

K_b = \dfrac{[\mathrm{CH_3NH_2}][\mathrm{OH^-}]}{[\mathrm{CH_3NH_3^+}]}

K_b = \dfrac{[\mathrm{CH_3NH_3^+}][\mathrm{H_3O^+}]}{[\mathrm{CH_3NH_2}]}

K_b = \dfrac{[\mathrm{CH_3NH_3^+}][\mathrm{OH^-}]}{[\mathrm{CH_3NH_2}]}

K_b = \dfrac{[\mathrm{CH_3NH_3^+}][\mathrm{OH^-}]}{[\mathrm{CH_3NH_2}][\mathrm{H_2O}]}