Jennifer obtains a fresh sample of an unknown solution (which does not contain H
ID: 1025608 • Letter: J
Question
Jennifer obtains a fresh sample of an unknown solution (which does not contain Hg,2 ions). She adds HCl(aq) toa sample of the unknown and observes the formation ofa white precipitate. After heating the precipitate in the supernatant, she finds that all of it dissolved. What can Jennifer most likely conclude about her unknown solution if no other chemical tests are performed? @ The unknown contains Pb only The unknown does not contain Pb2+. The unknown does not contain Cl. The unknown contains neither Pb2+ nor Ag. © The unknown contains Ag", Pb, or both. A B.HCDHE.Explanation / Answer
Consider the reaction Pb(NO3) + 2 HCl==2HNO3 + PbCl2
The precipitate PbCl2 formed will be white colour.
When heat is applied, the precipitate begins to disappear.
PbCl2(s) == Pb2+(aq)+ 2Cl- (aq)
The solubility product expression is
Ksp= [Pb 2+][Cl]2-
That is, Ksp exceeds.
When product exceeds the Ksp the solution is super saturated and precipitation occurs the concentrations will become small enough that their product does not equal to Ksp.
By cosidering Ag+,
Ag(NO3) + 2HCl == 2HNO3+AgCl2
But silver chloride doesnot dissolve in water. The forces holding the solid silver chloride lattice together are too strong to overcome by the forces that favours the formation of hydrated ions of Ag+ and Cl- .On heating,silver chloride is converted to Ag and chlorine which may occur in grey or purple in colour.
Hence the answer is option (a).The unknown contains Pb2+ only.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.