# Equilibrio of a sparingly soluble ionic compound

• Chemistry
Homework Statement:
Calculate the concentration of the first cation until second cation just starts to precipitate as sulfate
Relevant Equations:
Ksp
I got the first question correct but I don’t understand the answer given for second question which is c (Pb^2+) = 8.4x10^-5 molL ^-1. It divided the concentrate for sulphate ion of Ag2SO4 into 2 , but it is the solubility right ? ## Answers and Replies

Borek
Mentor
This is very difficult to read It divided the concentrate for sulphate ion of Ag2SO4 into 2

As far as I can tell - it didn't. My answer is 4.33 x 10^-5, but answer given is 8.4x10^-5, how can I get it?

Borek
Mentor
Next time please type the answer (takes less time than writing and taking pictures).

As far as I can tell answer given is wrong, your approach looks OK.

Sorry, my computer have problems that time, I can just upload using phone. Therefore, is it the given answer is wrong?

Borek
Mentor
Looks like, I got the same answer you did.

• daphnelee-mh
chemisttree
Science Advisor
Homework Helper
Gold Member
Were you given the Ksp for PbSO4?
Wikipedia has it at 2.13X10^-8 (20C), the CRC has it at 1.06X10^-8 (18C) and you are using 1.3X10^-8!