2. In a test tube containing a precipitate of PbCro, in water: What are the conc

Question

2. In a test tube containing a precipitate of PbCro, in water: What are the concentrations of the lead(Il) and chromate ions in equilibrium with the solid? Show your calculations. Use the Ksp from the Prelab table above. 3. How can AgCI(s) be dissolved completely? a) Write an equation for the reaction. 4. If HCI is added to a solution containing the following ions; Ag', Mg", K', and Ba*, which ion(s) should precipitate based on your prelab Table? 5. If sulfuric acid is added to a solution containing the following possible ions: Ag, Ca2 , NH4', and Pb, which ions should precipitate ?

Explanation / Answer

2. Ksp of PbCrO4 = 2.8 x 10^-13

Ksp = [Pb2+][CrO4^2-]

let x amount of PbCrO4 is in solution

2.8 x 10^-13 = (x)(x)

molar solubility = (x) = sq.rt.(2.8 x 10^-13)

                         = 5.29 x 10^-7 M

so,

[Pb2+] in solution = 5.29 x 10^-7 M

[CrO4^2-] in solution = 5.29 x 10^-7 M

3. adding aqueosu NH3 dissolves AgCl(s)

(a) Equation,

AgCl(s) + 2NH3 ---> [Ag(NH3)2Cl](soluble)

4. Among the given cations, AgCl has the lowest Ksp value and thus AgCl would precipitate first when HCl is added.

5. Pb2+ would precipitate first when H2SO4 is added to the mixture as Ksp of PbSO4 is lowest.

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