chem

Section: Ionization expressions, Weak Bases

Using the equilibrium constants listed in your book, arrange the following .1 M aqueous solutions in order of increasing pH.
a)NaNO2
b)HCl
c)NaF
d)Zn(H2O)3(OH)(NO3)

Here's what I have so far:
a) NaNO2 --> Na+ + NO2-
NO2- + H2O <==> HNO2 + OH-
b) HCl + H2O <==> Cl- + H3O+
c) NaF --> F- + Na+
F- + H2O <==> HF + OH-
d) Zn(H2O)3(OH)(NO3) --> Zn(H2O)3(OH)+ + NO3-
NO3- + H2O <==> HNO3 + OH-

and I have the following constants available to me:

Ka:
HNO2= 6.0 x 10^-4
HF= 6.9 x 10^-4
Zn(H2O)4 +2= 3.3 x 10^-10

Kb:
NO2- = 1.7 x 10^-11
F- = 1.4 x 10^-11
Zn(H2O)3OH+ = 3.0 x 10^-5

I'm not sure what to do from here. Also, I'm thinking my equations for B and D are wrong, because none of the information/constants provided would help solve what I have now (also, B is Hydrochloric ACID, is it not?) Any help with this problem would be much appreciated.


Consider (a).
NO2- + H2O ==> HNO2 + OH-
Kb = (HNO2)(OH-)/(NO2-)
You start with 0.1 M NO2- and (HNO2)=(OH-)=0
When x mols NO2- reacts with H2O, x mols HNO2 and x mols OH- are formed.

At equilibrium, (HNO2) = x; (OH^-) = x; (NO2-) = 0.1-x.
Plug those into the Kb expression and solve for x = (OH^-), convert that to pOH and that to pH.

Do the same for all, then arrange in increasing order of pH.

HCl is a strong acid and has no Ka; that is why you can't find it. It is 100% ionized; therefore, (H^+) = 0.1 M and pH = ?

D is incorrect. NO3- is the anion of HNO3 which is a strong acid, like HCl, therefore, NO3- is not hydrolyzed. But look in your text for the hydrolysis of cations that are complex ions.

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