Question

21. PART A. A solution contains 1.45×10^-2 M calcium acetate and 1.36×10^-2 M iron(II) nitrate.  
Solid potassium carbonate is added slowly to this mixture.

1) What is the formula of the substance that precipitates first?

formula =

_________

2) What is the concentration of carbonate ion when this precipitation first begins?  
[CO₃^2-] = ________ M

PART B. A solution contains 1.27×10^-2 M zinc nitrate and 7.32×10^-3 M nickel(II) acetate.  
Solid potassium cyanide is added slowly to this mixture.

1) What is the formula of the substance that precipitates first?

formula = _______

2) What is the concentration of cyanide ion when this precipitation first begins?  
[CN^-] = ________M

PART C. A solution contains 1.00×10^-2 M sodium hydroxide and 1.27×10^-2 M ammonium carbonate.  
Solid copper(II) acetate is added slowly to this mixture.

1) What is the formula of the substance that precipitates first?

formula =

_______

2) What is the concentration of copper(II) ion when this precipitation first begins?  
[Cu²⁺] = _______M

Answer 1

PART A.

Ksp of CaCO3 = 3.8 x 10^-9

Ksp of FeCO3 = 3.5 x 10^-11

1)

formula of the precipitate = FeCO3

2)

FeCO3 -------------> Fe2+   +    CO32-

Ksp = [Fe2+] [CO32-]

3.5 x 10^-11 = (1.36 x 10^-2) [CO32-]

[CO32-] = 2.57 x 10^-9 M

Part B)

Ksp of Zn(CN)2 = 8.0 x 10^-12

Ksp of Ni(CN)2 = 3.0 x 10^-23

¹⁾

formula of the precipitate = Ni(CN)2

2)

Ni(CN)2 ----------> Ni2+   +   2 CN-

Ksp = [Ni2+] [CN-]^2

3.0 x 10^-23 = (7.32 x 10^-3) [CN-]^2

[CN-] = 6.40 x 10^-11 M

Part C)

Ksp of Cu(OH)2 = 1.6 x 10^-19

Ksp of CuCO3 = 2.5 x 10^-10

1)

formula of precipitate = Cu(OH)2

2)

Cu(OH)2 -------------> Cu2+   +   2 OH-

Ksp = [Cu2+][OH-]^2

1.6 x 10^-19 = [Cu2+] (1.00 x 10^-2)^2

[Cu2+] = 1.60 x 10^-15 M