Xque
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Registered: 8-11-2005
Location: Europe
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Equilibrium concentration of sulphate ions
Barium and strontium reacts with a 0.5 M solution of Na2SO4. Assume that 0,05 ml Na2SO4 has been used (a surplus) , that the total volume is 1 ml and
pH=1. Calculate the equilibrium concentration of sulphate ions.
This is what I've found so far:
Na2SO4 (aq) + H2O (l) -> 2 Na+ (aq) + SO42- (aq)
SO42- (aq) + H2O (l) -> HSO4- + (aq) + OH- (aq)
Ks = [HSO4-] * [OH-] / [HSO42-]
Ks = 1,02 * 10^-2 M (I am supposed to use Ks for HSO4-, right?)
[NA2SO4] = 0,5 M * 0,05 ml / 1 ml = 25 * 10^-3
[HSO4-] + [SO42-] = [Na2SO4]
pH = 1
pH + pOH = 14 =>
pOH = 13 => [OH-] = 10^-13 M.
Now I'm lost. I just recently gained understanding of the whole idea of equilibrium calculations and this problem is quite a thing .
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Darkblade48
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Registered: 27-3-2005
Location: Canada
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I'm thinking that you would need to find the Ksp of barium sulfate and strontium sulfate first (in a table in a textbook, or on the internet).
They will react with the SO4 ions in solution to form the insoluble precipitate. From there, you can calculate the amount of SO4 ions using the
equilbrium table (ICE table)
And if this is wrong, it's 5:30 am local time 
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