Hi, there. Just a little problem with some senior chemistry in highschool. Only 2 questions.
1.) A solution contains 0.0100 M TlNO3 and 0.0100 M AgNO3.
a) Which compound precipitates first when solid NaI is slowly added to 100. mL of this solution? (Ksp TlI = 8.90 x 10^-8 ; Ksp AgI = 1.50 x 10^-16)
b) What mass of this ion remains unprecipitated when the second compound begins to precipitate (Answer: 1.81 x 10^-1 mg...we have to show our work, don't know what to do)
2.) A 1.00 L solution contains 100. mg of Ba+2 and 10.0 g of Sr+2. Within what range must the concentration of CrO4-2 be in order to precipitate Ba+2 without precipitating any Sr+2?
(Ksp BaCrO4 = 1.20 x 10^-10 ; Ksp SrCrO4 = 3.60 x 10^-5)
(Answer: 1.65 x 10^-7 < [CrO4-2] < 3.16 x 10^-4)
So, our teacher does give us the answers, however, we need to show the work and how we obtain the answer. For some, I'm sure those problems were very easy. The thing is, she hasn't gone into depth like this, and our textbooks do not cover solubility problems like these ones, just the basic ones.
For the first one, I assumed that the nitrate ions just act as spectators and do not get involved in the reaction when the Tl and Ag react with the iodide ion. I then did something like this:
ksp = [Ag+][I-]
1.50 x 10^-16 = (1.00 x 10^-2)[I-]
[I-] = 1.50 x 10^-14
ksp = [Tl+][I-]
8.90 x 10^-8 = (1.00 x 10^-2)[I-]
[I-] = 8.90 x 10^-6
I figured that either of those I values would tell me which precipitates first..but then I kind of lost myself in where I was going. For the second question, well I am kind of lost. I fooled around with a bunch of calculations for a good hour and ended up with a headache...if you can help, great. Thanks