Solubility Product

2010-04-04 7:49 am

An aqueous solution that is 2.00 M is AgNO3 is slowly added from a burette to an aqueous solution that is 0.01 M in Cl- and also 0.01 M in I-. Ksp of AgCl (s) and AgI (s) are 1.8*10^-10 and 8.5*10^-7 respectively.
(a) What ion, Cl- or I- ion, is the first to precipitate from solution?
(b) When the second ion begins to precipitate, what is the remaining concentration of the first ion?
(c) Find the percentage of first ion remaining in the solution when the second ion begins to precipitate.

回答 (1)

胡雪8°

2010-04-04 9:45 am

✔ 最佳答案

The Ksp of AgI is 8.5 x 10^-17, but NOT 8.5 x 10^-7.

(a)
Both AgCl and AgI precipitates are in the same form of MX, and AgI has a smaller Ksp.
Hence, AgI is the first to precipitate from solution.
（Notice that the Ksp of AgI is 8.5 x 10^-17 instead.）

(b)
Assume that the change in volume is negligible when AgNO3 is negligible, because AgNO3 is much concentrated than Cl^- and I^-.

[Ag^+] when AgCl begins to precipitate
= (1.8 x 10^-10) / 0.01
= 1.8 x 10^-12 M

[I^-] when AgCl begins to precipitate
= (8.5 x 10^-17) / (1.8 x 10^‑12)
= 4.72 x 10^-5 M

(c)
% of I^- remaining in the solution when Cl^- ion begins to precipitate
= [(4.72 x 10^-5) / 0.01] x 100%
= 0.472%

2010-04-04 01:52:30 補充：
Mistyping in (b):
(b)
Assume that the change in volume is negligible when AgNO3 is "added" ......

參考: 胡雪八

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