Question

PbBr2 will be least soluble in which of the following? Ksp of PbBr2 is 4.6*10^-6. Show your calculations on the molar concentration of PbBr2 to support your answer. Options are: A) water B) 0.10 M Pb(NO3)2 C) 0.15 M KBr

Answer 1

PbBr₂ ?Pb²⁺ + 2Br^-

at equlibrium, concentrations of species are (assuming x moles of PbBr2 is dissolved): 1-x, x, 2x respectively for PbBr2, Pb2+, Br- ions

therefore, Ksp = 4.6x10^-6 = 4x³

x = 0.0105 M

Concentration of Pb2+ = 0.0105 M, [Br-] = 0.021 M.

That is, 0.0105 moles of PbBr2 dissolves in 1000 mL of water.

B) A 0.1 M Pb(NO3)2 solution contains 0.1 M Pb²⁺ ions, thus the Ksp = (0.1)4x² = 4.6x10^-6 (assuming 0.1 + x ~ 0.1)

x = 0.00339 M . that is 0.00339 moles of PbBr2 dissolves in 1000 mL of 0.1M Pb(NO3)2 solution

C) A 0.15M KBr solution contains 0.15 M Br- ions, therefore, Ksp = (x)(0.15 + 2x)² = 4.6x10^-6 (assuming again x is low compared to 0.15)

or 0.0225x = 4.6x10-6 and solving for x, x = 0.0002 M

That is, 0.0002 moles of PbBr2 dissolves in 1000mL of 0.15M KBr solution.

Thus, PbBr2 is least soluble 0.15M KBr solution.