Question

Hydroxylamine is a weak base that readily forms salts used as antioxidants in soaps. What is the pH of a 0.025M hydroxylamine solution that has a Kb of 9.1x109 ?

Answer 1

                     NH2OH               NH₂⁺ +            OH^-

initial               0.025M                                 0                                     0

change          - 0.025 x                              +0.025x                        +0.025x

equilibrium                            0.025(1-x)                             0.025 x    0.025x         

Kb = [NH₂⁺ ] [OH-]/ [NH2OH]

     = 0.025 x    * 0.025 x    / 0.025(1-x)    

   = 0.025 X²    / (1-X)

9.1x10^-9 = 0.025 X²

X² = 9.1x10^-9 / 0.025

BY SIMPLYFYING:

X = 6.03*10^-4

Hence [OH-] = 0.025 X = 0.025 * 6.03*10^-4

                        = 15* 10^-6

pOH = -log [15* 10^-6]

         = 4.82

Hence pH = 14-pOH

                   = 9.18