Question

A solution contains 1.36×10^-2 M lead nitrate and 8.64×10^-3 M silver acetate.
Solid ammonium chromate is added slowly to this mixture.

A. What is the formula of the substance that precipitates first?

formula =

B. What is the concentration of chromate ion when this precipitation first begins?
[chromate] =

M

Answer 1

the Ksp data:

PbCrO4 3×10–13

Ag2CrO4 1.12×10–12

from this, get [CrO4-2] required for eath

i) PbCrO4

Ksp = [Pb+2][CrO4-2]

(3*10^-13 = (1.36*10^-2)([CrO4-2])

[CrO4-2] =(3*10^-13)/(1.36*10^-2) = 2.20*10^-11 M

ii)

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

1.12*10^-12 = (8.64*10^-3)^2 * [CrO4-2]

[CrO4-2] = (1.12*10^-12)/((8.64*10^-3)^2) = 1.500*10^-8 M

clearly, PbCrO4 requires less CrO4-2 to precipitate

choose

PbCrO4

b.

finc CrO4-2 when it precipitates -.> [CrO4-2] = 2.20*10^-11 M