[sweetsach]

Hi guys. .. i am having some problems understanding some concepts here...

Problem1:
We know that the molar solubility of BaCO3 is 7.1X10^-5 and that of BaSO4 is 1.1X10^-5.
So when 0.50 F Na2CO3 is added to a clear saturated solution of BaSO4, a BaCO3 precipitate is formed.
How is this possible given the fact that BaCO3 is more soluble than BaSO4??

Problem2:
Correct the following wrong statements:
a)Of 2 slightly soluble compounds, the one with the larger Ksp is the more soluble.
b)For MgCO3, the Ksp=5.3X10^-8. This means that in all solutions containing MgCO3, [Mg2=]=[CO3-2] and the [Mg2=][CO32-]=5.3X10^-8

For problem1, i just have no clue on what to look at...

For problem2, a) this is wrong because we are talking about "slightly soluble compounds"... i am really not sure how this works though...
and for b) the concentration of Mg2= is not necessarly equal to that of CO3 -2

I am extremely lost... some help would be very very much appreciated...
Thank you...

[Borek]

When does the precipitation of the given salt starts?