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October 20, 2014

October 20, 2014

Posted by **Sigurd** on Tuesday, April 8, 2008 at 8:21pm.

a caluculation to figure out whether a precipitate will form and i'm struggling with the second half too!

- Ksp/Ka Questions-Chem -
**DrBob222**, Tuesday, April 8, 2008 at 8:47pmJust remember what Ksp is!!

Ksp, in this case for PbCl2, = 1.7 x 10^-5. What does that mean? It simply means that (Pb^+2)(Cl^-)2 MAY NOT EVER EXCEED 1.7 x 10^-5. So you calculate the product of those concns, (raise each to the power, of course, in the balanced equation) and if that number is higher than Ksp, a ppt will occur. If that number is less than Ksp, no ppt will occur. If that number is the same as Ksp, then the solution is exactly saturated and the next Pb ion and Cl ion added to that solution will ppt (1 molecule of PbCl2).

mols lead (II) nitrate = M x L = ??

mols NaCl = M x L = ??

(Pb^+2) = mols/L (remember to add mL lead nitrate to mL NaCl to find total mL of solution. We assume the volumes are additive.

(Cl^-) = mols/L.

Then (Pb^+2)(Cl^-)^2 = ?? and compare with Ksp.

Let me know if this isn't clear.

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