Question

calculate the pH and fraction of dissociation of a 0.0247 M benzylamine solution

Answer 1

Kb of benzyl amine is 2.2 × 10⁻⁵ (from text book)

C6H5NH2 + H2O <======> C6H5NH2+ + OH-

I 0.0247 0 0

C -x +x +x

E 0.0247-x +x +x

Kb = [C6H5NH2+][OH-] / [C6H5NH2]

2.2 × 10⁻⁵ = [x][x]/0.0247-x]

x² +  x2.2 × 10⁻⁵ -5.434 x 10^-7 =0

solve the quadratic equation

x = 0.0007262 = [OH-] = [C6H5NH3+]

pOH = -log[OH-]

pOH = -log[0.0007262]

pOH = 3.14

pH = 14-pOH

pH = 14-3.14

pH = 10.86

Fraction of dissociation = concentration of C6H5NH3+ / Concentration of C6H5NH2

=0.0007262 / 0.0247

= 0.0294