Question

Silver ion is being considered as a reagent for separating 103) from CO32- in a solution that is 0.060 M in K2CO3 and 0.070 M in NalO3. Which anion will precipitate first when silver ion is added to the solution and what will its concentration be when the second anion begins to precipitate? Can the two ions be separated with 99.99% efficiency? (6pts) Ksp = 3.1 x 10-8 for Agl03 Ksp = 8.1 x 10-12 for Ag2CO3

Answer 1

Ksp of AgIO3 = 3.1 x 10^-8

[Ag+] [IO₃-] = 3.1 x 10^-8

[IO₃-] = 0.07 M

=> [Ag+] = 3.1 x 10^-8/ 0.07

= 4.43 x 10^-7 M

Ksp of Ag₂CO₃ = 8.1 x 10^-12

[Ag+]₂ [CO₃^2-] = 8.1 x 10^-12

[CO₃^2-] = 0.06 M

=> [Ag+]² = 8.1 x 10^-12 / 0.06

[Ag+] = 1.16 x 10^-5 M

a)

Anion IO₃- will precipitate first since it requires lower concentration of Ag+ ions for precipitation.

b)

[Ag+] [IO₃-] = 3.1 x 10^-8

Ag₂CO₃ starts to precipitate when [Ag+] = 1.16 x 10^-5 M

[IO₃-] = 3.1 x 10^-8 / 1.16 x 10^-5 M

= 2.67 x 10^-3 M

c)

When Ag₂CO₃ starts to precipitate,

[IO₃-] = 2.67 x 10^-3 M

[CO₃^2-] = 0.06 M

Efficiency of separation = 100 - [IO₃-] * 100 / [CO₃^2-]

= 100 - 2.67 x 10^-3 * 100 / 0.06

= 95.6 %