Why treat Pb2+ and CrO42- precipitation as completion before Ksp

  • Thread starter Thread starter RoboNerd
  • Start date Start date
  • Tags Tags
    Ksp Theory
Join the discussion
Registration is free. Start your own thread to ask a follow-up.
Sign up Log in
1 reply · 3K views
RoboNerd
Messages
410
Reaction score
11

Homework Statement



[/B]
Lead chromate, PbCrO4, is a yellow pigment used in paints. Suppose 0.50 L of a 1.0 x 10-5 M Pb(C2H3O2) and 0.50 L of a 1.0 x 10-3 M K2CrO4 solution are mixed. Calculate the equilibrium concentration of Pb+2 ion remaining in the solution after PbCrO4 precipitates. What is the percentage of Pb+2 remaining in solution after the precipitation has occurred. (The Ksp for PbCrO4 is 1.8 x 10-14)I have a little question regarding theory about how a website solved this problem.

Homework Equations


The solution is here on page 21 of the document.
http://faculty.icc.edu/bcook/chem132NT/acid_base_eq.pdf

The Attempt at a Solution



My question is this: is it really necessary to assume initially that this is a limiting reagent problem and have the reaction of Pb2+ and CrO42- go to completion to form the salt and then do the ICE chart calculation for the solubility, or is it OK if I just go and do the ice chart straight away?

I tried both methods, and both gave the same numerical answer, but which approach is more "legit"?

Thanks in advance.
 
Physics news on Phys.org

Discussion

"ICE?" If you have to use it to satisfy "OC" types, do so. Otherwise, plug it in and grind it out.