Dale S. answered • 05/05/20
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Great Day Barney!
The good old common ion effect!
Need to make 1 assumption and research the Ksp for Tl(OH)3.
Assumption that NH3 a weak base reacts with H2O to form ammonium ion and hydroxide ion.
Hydroxide ion = concentration of .1M
Write dissociation equation for Tl(OH)3(s) → Tl+3(aq) + 3OH-1(aq)
Write equilibrium expression for solubility = Ksp = [Tl+3(aq)][OH-1(aq)]3
Let solubility = s therefore the solubility of Tl =s and OH = 3s , because there are 3 times as many OH ions as Tl ions in a saturated solution.
Ksp for Tl(OH)3 = 6.3 x 10 -46 per google.
Substitute in the equilibrium equation .
6.3 x 10-46 = [ s] [3s]3 now the tricky part Tl(OH)3 is dissolved in .10 M NH3 or OH- .
we can assume that .10 M >>>>> s ( is much greater than s) ; therefore we can substitute .10M for 3s in the equilibrium solubility equation and the equation is rewritten as follows:
6.3 x 10-46 = [s] [.10M]3
solve for s which is the molar solubility for Tl the molar solubility for OH- = .10M
s = 6.3 x 10-43 M = molar solubility for Tl.
As you can see .10M is much larger than s( the molar solubility of Tl(OH)3) , our assumption is valid.
This calculation is determining the concentration of ions in a saturated solution of the given compound.
Can be done without the assumption, but the quadratic formula must be used and not necessary when s is so small.
