A solution consists of 0.2M NH4OH and 0.2M NH4Cl. If Kb of NH4OH is 1.8 × 10^5, the [OH-] of the resulting solution is ?

A solution consists of 0.2M NH4OH and 0.2M NH4Cl. If Kb of NH4OH is 1,8x10^-5, the [OH-] of the resulting solution is ?

A. 3,6x10^-5

B. 3,2x10^-5

D. 1,8x10^-5

C. 0,9x10^-5

SOLUTION

NH4OH and NH4Cl is a buffer solution:

POH = PKb + log [salt]/[base]

Concentration of NH4OH = 0,2 M

Concentration of NH4Cl = 0,2 M

PKb of NH4OH = 1,8x10^-5      

POH = - log 1,8x10^-5 + log [0,2]/[0,2]

POH = - log 1,8x10^-5  

-log [OH-] = - log 1,8x10^-5 

[OH-] = 1,8x10^-5

well, the concentration of [OH-] is 1,8x10^-5