Question

A solution contains 9.78×10^-3 M calcium nitrate and 6.57×10^-3 M iron(II) acetate.
Solid ammonium carbonate is added slowly to this mixture.

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

formula =

B. What is the concentration of carbonate ion when this precipitation first begins?
[CO₃^2-] = ______M

Answer 1

Two precipitates are possible to form

Calcium Carbonate and Iron Carbonate

Ksp of Calcium Carbonate = 3.3×10^-9

Ksp of Iron(II) Carbonate = 1.28 ×10^-11

A) Ksp of Iron(II) Carbonate is low ,so it will precipitate first

the formula is FeCO3

B) Concentration of Iron(II)acetate = 0.00657M

Concentration of Fe2+ = 0.00657M

FeCO3(s) <-------->Fe2+(aq) + CO32-(aq)

Ksp = [ Fe2+] [ [ CO32-]

1.28 ×10^-11 M^2= 0.00657 M× [ CO32-]

[ CO32-] = 1.28×10^-11M^2/0.00657M

= 1.95×10^-9M

So, When precipitation first begins , [ CO32-] = 1.95×10^-9M