In: Chemistry
Calculate the equilibrium concentration of OH-, HNO2, NO2-, and H3O+, and the ph at 25 degree C of a solution that is 0.25 M in NaNO2? Comment
HNO2 , Ka = 5.6 x 10^-4
Kb = Kw / Ka = 1.0 x 10^-14 / 5.6 x 10^-4
Kb = 1.79 x 10^-11
NO2 - + H2O -----------------------------> HNO2 + OH-
0.25 0 0 --------------> initial
0.25-x x x ------------------> equilibrium
Kb = [HNO2][OH-]/[NO2-]
Kb = x^2 / 0.25-x
1.79 x 10^-11 = x^2 / 0.25-x
x^2 + 1.79 x 10^-11 x - 4.46 x 10^-12 =0
x = 2.11 x 10^-6
[OH-] = [HNO2] = x
[OH-] = [HNO2] = 2.11 x 10^-6 M
[NO2-] = 0.25 -x = 0.2499 = 0.25 M
[H3O+] = Kw / [OH-] = 1.0 x 10^-14 / 2.11 x 10^-6
[H3O+] = 4.74 x 10^-9 M