A 100 mL sample of a clear nitrated solution of Ag2S04 is added to 250 mL of a c
ID: 483423 • Letter: A
Question
A 100 mL sample of a clear nitrated solution of Ag2S04 is added to 250 mL of a clear solution of saturated PbCrO4. will precipitate form? (hint: what are the concentrations of all ions in each of the saturated solution before they are mixed?) A 100 mL sample of a clear nitrated solution of Ag2S04 is added to 250 mL of a clear solution of saturated PbCrO4. will precipitate form? (hint: what are the concentrations of all ions in each of the saturated solution before they are mixed?) A 100 mL sample of a clear nitrated solution of Ag2S04 is added to 250 mL of a clear solution of saturated PbCrO4. will precipitate form? (hint: what are the concentrations of all ions in each of the saturated solution before they are mixed?)Explanation / Answer
You do indeed need the initial concs of the cmpds which you get from the fact that initially the solns are saturated. For Ag2SO4
Ag2SO4(s) 2Ag^+ + SO4^2-
Ksp = [Ag^+]^2[SO4^2-] = 1.4 x 10^-5
Let s mol dissolve, hence [Ag^+] = 2s; [SO4^2-] = s
Hence 4s^3 = 1.4 x 10^-5 s = 0.0152 M .: [Ag^+] = 0.0304M
When solns are mixed conc decreases (M1V1 =M2V2):
[Ag^+] = 0.0304×100/350 = 8.68 x 10^-3 M and
[SO4^2-] = 4.34 x 10-3 M
Similarly for PbCrO4
PbCrO4(s) Pb^2+ + CrO4^2-
Ksp = [Pb^2+ ][CrO4^2-] = 2.8 x 10^-13
s^2 = 2.8 x 10-13 s = 5.29 x 10^-7 M
Upon dilution 5.29 x 10^-7×250/350 = 3.78 10^-7 M = [Pb^2+ ]= [CrO4^2-]
Will Ag2CrO4 ppt?
Ksp = [Ag^+]^2[CrO4^2-] = 1.1 x 10-12
[8.68 x 10^-3]^2[3.78 x 10^-7] = 2.8(5) x 10-11 which is > 1.1 x 10-12 so some
Ag2CrO4 will ppt.
Will PbSO4 ppt?
Will Ksp = [Pb^2+ ][SO4^2-] = 1.6 x 10^-8
[3.78 x 10^-7][4.34 x 10-3] = 1.6(4) x 10^-9 so PbSO4 will not ppt.
Check my calculations.
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