Question

1) Determine pH of a 0.13 M ammonia solution.

2) Determine pOH of a 0.13 M ammonia solution.

Answer 1

we know that

ammonia is a weak base

and

Kb for ammonia is 1.8 x 10-5

now

NH3 + H20 ---> NH4+ + OH-

now

at equilibrium

[NH4+] = [OH-] = y

[NH3] = 0.13 - y

so

Kb = [NH4+] [OH-] / [NH3]

so

1.8 x 10-5 = [y] [y] / [0.13-y]

1.8 x 10-5 ( 0.13 - y) = y2

y = 1.5207 x 10-3

so

[OH-] = 1.5207 x 10-3

we know that

pOH = -log [OH-]

so

pOH = -log 1.5207 x 10-3

pOH = 2.818

so

the value of pOH is 2.818

now

pH = 14 - pOH

so

pH = 14 - 2.818

pH = 11.182

so

pH of the solution is 11.182