Calculate the pH of 0.11MNaNO2; Ka for HNO2 is 4.6×10^−4.
express the answer to two decimal places
NaNO2 when mixed in water will form:
Na+ and NO2- ions
then
NO2- + H2O <--> HNO2 + OH-
this is a basic salt, it will free OH- ions
then
Kb = [HNO2][OH-]/[NO2-]
Kb = Kw/Ka = (10^-14)/(4.6*10^-4) =2.1739*10^-11
note that in equilibrium
[HNO2] = x = [OH-]
[NO2-] = 0.11 -x
then
Kb = [HNO2][OH-]/[NO2-]
2.1739*10^-11 = (x*x)/(0.11-x)
solve for x
x = [OH-] = 1.546*10^-6
pOH = -log(OH) = -log(1.546*10^-6) = 5.81079
pH = 14- pOH = 14-5.81079 = 8.18921
pH = 8.19
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