The Ksp of PbCO3 and MgCO3 are 1.5 X 10-15 and 1X10-15 respectively at 298 K. The concentration of Pb+2 ions in a saturated solution containing MgCO3 and PbCO3 is –
(a)1.5 X10-4
(b)3X10-8
(c)2X10-8
(d)2.5X10-8

Question

The Ksp of PbCO3 and MgCO3 are 1.5 X 10-15 and 1X10-15 respectively at 298 K. The concentration of Pb+2  ions  in a saturated solution containing MgCO3  and PbCO3 is –
(a)1.5 X10-4
(b)3X10-8
(c)2X10-8
(d)2.5X10-8

rushwr · Answer

Hey what do u think the answer is ?

anonymous · Answer

I think that the ans is option (c). Not really sure about it though ..........

rushwr · Answer

how did you find it?

anonymous · Answer

I didn't this was the ans given in my book ………………..
 Since quite a few ans in that book have proven to be incorrect I am not really positive that this is the right ans.
If I knew the solution to the question I wouldn't be asking for it on openstudy

cuanchi · Answer

Yea I didn't get any of the answers.What is your strategy to solve the problem?

photon336 · Answer

Well for starters Haha 

$$PbCO _{3} (Aq) --> Pb ^{2+} + CO _{3}^2- $$

$$K _{sp} = [x][x] = [Pb ^{2+}][CO _{3}^2-]$$

$$MgCO _{3}--> Mg _{2+} + CO _{3}^2-$$


$$K _{sp} = [x][x] = Mg ^{2+} CO _{3}^2- $$

cuanchi · Answer

well done
the PbCO3 (s) it is insoluble, that is the reason you dont include in the Ksp, the ions are (aq)
PbCO3(s)−−>Pb2+(aq)+CO23−(aq)

then we have the common ion CO23−(aq) effect in the solubility

photon336 · Answer

@Cuanchi thanks for pointing that out.. i forgot most of the solubility rules, but I never saw a problem where we are given two Ksp values

kash_thesmartguy · Answer

@Jaynator495