Na is right.
The others are not. Na2SO3 is a salt and when it dissolves the SO3^2- hydrolyzes.
Na2SO3 ==> 2Na^+ + SO3^2-
1.17M.....2*1.17...1.17
.......SO3^2- + HOH --> HSO3^- + OH^-
I......1.17..............0........0
C.......-x...............x........x
E.....1.17-x.............x........x
Kb for SO3^2- = (Kw/Ka2 for H2SO3) = (x)(x)/(1.17-x)
Solve for x = OH^- = HSO3^-
I didn't solve this but the number is relatively small; I'll just call it y and use that below.
Then HSO3^- hydrolyzes to
...........HSO3^- + HOH ==> H2SO3 + OH^-
I...........y................0.......0
C...........-z...............z.......z
E...........y-z..............z.......z
Then
Kb for HSO3^- = (Kw/k1 for H2SO3) =
(z)(z)/(y-z).
You really don't need to solve this for the following reasons.
Look at Kb = Kw/k1 = 1E-14/1.4E-2 = about 1E-12 which is a very small number. So whatever you started with at y can subtract a small z and still essentially be y. Then look at z. That's so small coming from this hydrolysis that it's basically what you started with. See the first hydrolysis you calculated OH and that was the same as HSO3^-. So if you write the hydrolysis equation out like this
Kh = Kw/k1 = (H2SO3)(OH^-)/(HSO3^-) you see that OH^- = HSO3^- so those cancel each other and (H2SO3) = Kh = (Kw/k1) = about 1E-12 from above.
Calculate the concentrations of all species in a 1.17 M Na2SO3 (sodium sulfite) solution. The ionization constants for sulfurous acid are Ka1 = 1.4× 10–2 and Ka2 = 6.3× 10–8.
I found Na+ = 2.34
SO3^2- = 1.17
H2SO3 = 7.14 x10^-13
I can't find
HSO3^- = ?
OH^- = ?
H^+ = ?
Please show steps. THANK YOU!
1 answer