A----Solid nickel(II) nitrate is slowly added to 75.0 mL of a 0.0652 M sodium cy

Question

A----Solid nickel(II) nitrate is slowly added to 75.0 mL of a 0.0652 M sodium cyanide solution. The concentration of nickel ion required to just initiate precipitation is ?.

Solid sodium iodide is slowly added to 50.0 mL of a 0.0490 M lead nitrate solution. The concentration of iodide ion required to just initiate precipitation is ?

B---A solution contains 7.65×10-3 M ammonium carbonate and 1.21×10-2 M potassium hydroxide.
Solid copper(II) nitrate is added slowly to this mixture.

What is the formula of the substance that precipitates first?

B. What is the concentration of copper(II) ion when this precipitation first begins?

A solution contains 1.31×10-2 M sodium iodide and 1.13×10-2 M ammonium bromide.
Solid lead acetate is added slowly to this mixture.

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

Explanation / Answer

A - concentration of Ni2+ required to intiate precipitation = Ksp/[CN-]^2

= 3 x 10^-23/(0.0652)^2

= 7.06 x 10^-21 M

Concentration of [I-] required for precipitation of PbI2 = sq.rt.(Ksp/[Pb2+])

= sq.rt(7.9 x 10^-9/0.0490)

= 4.01 x 10^-4 M

B - A) The first precipitate to form here would be the one with lower Ksp values

So, Cu(OH)2 will precipitate first

B) concentration of [Cu2+] ion when first precipitation occurs = Ksp/[OH-]^2

= 2 x 10^-19/(7.65 x 10^-3)^2

= 3.42 x 10^-15 M

C - The formula of first substance to precipitate would be PbI2

concentration [Pb2+] when precipitation begins = 7.9 x 10^-9/(0.0131)^2 = 4.60 x 10^-5 M

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