In: Chemistry
Calculate the percent ionization of nitrous acid in a solution that is 0.241 M in nitrous acid (HNO2) and 0.195 M in potassium nitrite (KNO2). The acid dissociation constant of nitrous acid is 4.50 ⋅ 10-4.
[HNO2] = 0.241 M
[NO2-] = 0.195 M
HNO2 <---------> H +
NO2-
0.241
M
0 0.195 M
(initial)
0.241-x
x 0.195+x (at
equilibrium)
Ka = [H+] [NO2-] / [HNO2]
4.5*10^-4 = x * (0.195+x) / (0.241-x)
Since Ka is small, x will be small and it can be ignored as
compared to 0.241 and 0.195
So, above expression becomes,
4.5*10^-4 = x * (0.195) / (0.241)
x = 5.56*10^-4 M
Percent dissociation = x*100 / 0.241
=(5.56*10^-4)*100 / 0.241
= 0.23 %
Answer: 0.23 %