1. Solid cobalt(II) acetate is slowly added to 75.0 mL of a 0.0506 M potassium h

Question

1. Solid cobalt(II) acetate is slowly added to 75.0 mL of a 0.0506 M potassium hydroxide solution. The concentration of cobalt(II) ion required to just initiate precipitation is M

Ksp Co(OH)2 = 2.5 × 10-16

2.A solution contains 1.32×10-2 M ammonium chloride and 1.01×10-2 M sodium iodide.
Solid lead nitrate is added slowly to this mixture.

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

B. What is the concentration of lead ion when this precipitation first begins?
[Pb2+] = M

3.A solution contains 1.32×10-2 M ammonium chloride and 7.89×10-3 M potassium chromate.
Solid silver acetate is added slowly to this mixture.

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

B. What is the concentration of silver ion when this precipitation first begins?
[Ag+] = M

Explanation / Answer

1. Co(OH)2 (S) <----> Co^+2(aq) + 2OH^-(aq)

   [OH-] = 0.0506 M

   [co+2] = ?

Ksp of Co(OH)2 = [co+2][OH-]^2

   (2.5*10^-16) = x*0.0506^2

x = [co+2] = 9.76*10^-14 M

2.

ksp of PbCl2 = 1.7*10^-5

ksp of PbI2 = 8.5*10^-9

A. formula of the substance that precipitates first = PbI2

B. ksp of PbI2 = [Pb+2][I-]^2

    (8.5*10^-9) = x*(1.01*10^-2)^2

x = [Pb+2] = 8.33*10^-5 M

3.

ksp of AgCL = 1.8*10^-10

ksp of Ag2CrO4 = 2*10^-12

A. formula of the substance that precipitates first = Ag2CrO4

B. ksp of Ag2CrO4 =[Ag+]^2[CrO4-2]

   [CrO4-2] = 7.89*10^-3 M

    [Ag+] = x

   (2*10^-12 ) = x^2*(7.89*10^-3)

   [Ag+] = x =1.59*10^-5 M

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