Question

Determine the concentration of a NaNO2 solution that has a pH of 8.22. Ka for HNO2...

Determine the concentration of a NaNO2 solution that has a pH of 8.22. Ka for HNO2 is 4.5 x 10-4

Homework Answers

Answer #1

Ka = 4.5 x 10-4

Kb = (1.0 x 10-14) / (4.5 x 10-4) = 2.2 x 10-11

pH = 8.22

So, pOH = 14 - pH = 14 - 8.22 = 5.78

- log [OH-] = 5.78

[OH-] = 10-5.78

[OH-] = 1.66 x 10-6

So,

Now,

NO2- will react as a base:

NO2- + H2O HNO2 + OH-
  

Kb = [HNO2] [OH-] / [NO2-]

2.2 x 10-11 = (1.66 x 10-6) (1.66 x 10-6) / [NO2-]

2.2 x 10-11 = (2.76 x 10-12) / [NO2-]

  [NO2-] = (2.76 x 10-12) / (2.2 x 10-11)

  [NO2-] = 1.25 x 10-1

So,   [NO2-] = 0.125 M

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