If 120 mL of 705104 M CuBr2 are added to 250 mL of 840105 M

If 12.0 mL of 7.05×10^-4 M CuBr₂ are added to 25.0 mL of 8.40×10^-5 M (NH₄)₂CO₃, will solid CuCO₃ (K_sp = 2.5×10^-10) precipitate? yes or no ?

If a precipitate will not form, what carbonate ion concentration will cause a precipitate of copper(II) carbonate to form? If a precipitate will form, what is the minimum [CO₃^2-] that could have been present without initiating precipitation? Assume the total volume used in the above example. M = ?

Solution

Molarity of CuBr2 = 12 x 7.05 x 10^-4 / 12 + 25

                           = 2.286 x 10^-5 M

Molarity of (NH₄)₂CO₃ = 25 x 8.40 x 10^-5 / 12 + 25

                                    = 5.676 x 10^-5 M

CuCO3   --------------> Cu+2 +   CO32-

Qsp = [Cu+2][CO32-]

       = (2.286 x 10^-5)(5.676 x 10^-5)

       = 1.30 x 10^-9

here Qsp > Ksp . so yes , precipitate wil form

b)

     CuCO3 -----------> Cu+2 +   CO32-

Ksp = [Cu+2][CO32-]

2.5 x 10^-10 = [ 2.286 x 10^-5][CO32-]

[CO32-] = 1.09 x 10^-5 M