Question

The pH of an aqueous solution of 0.538 M ethylamine (a weak base with the formula C₂H₅NH₂) is _________

Answer 1

      C2H5NH2   + H2O ----------------- C2H5NH3+ + OH-

         0.538                                              0                0

            -x                                                +x              +x

      0.538-x                                               +x              +x

        kb of C2H5NH2= 4.3x10^-4

        Kb = [C2H5NH3+][OH-]/[C2H5NH2]

4.3x10^-4 = x*x/( 0.538-x)

for solving the equation

x= 0.0149

[OH-] = 0.0149M

-log[OH-] = -log( 0.0149)

POH= 1.827

PH+POH=14

PH=14-POH

PH=14-1.827

PH=12.173

PH= 12.17