BR chemistry chapter 3 passage 11 # 72

[bleach121]

Enough CaCl2 is added to water so that not all of it dissolves, and thus some CaCl2 remains as a solid on the bottom of the flask. The [CI] is then measured. Addition of which of the following to the solution will increase the chloride ion concentration ([CI])?

Water
Silver nitrate
Calcium fluoride
Sodium phosphate

The answer is Sodium phosphate. I'm confused why the answer can't be Silver nitrate.
CaCl2 --> Ca2+ + 2Cl-
So wouldn't you generate more Cl- in solution if you remove either of the products (Ca2+ OR Cl-)? Thus if you add AgNO3, the AgCl will precipitate and remove Cl- from solution causing more Cl- to dissociate. Why isn't this considered as a possibility?
Thanks.

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[gettheleadout]

One thing to be remembered in the application of Le Châtelier's Principle is that a system never completely negates the stress placed upon it.

First of all, the solution of CaCl2 is already saturated, and if you add silver nitrate you'll precipitate out AgCl and initially lower the [Cl]. This right here should tell you this is a terrible way to try and accomplish an overall increase in [Cl]. Some additional solid CaCl2 will dissolve as AgCl is precipitated out, but now the [Ca2+] will be higher and thus contribute more to the ion product than it would if the Ca2+ : Cl– ratio was a flat 1 : 2. This means that after the [Cl] drops as AgCl crashes out and the [Cl] starts to rebound, it won't even make it as high as it was before. Silver nitrate would overall decrease the [Cl].

The clear solution is to instead reduce the [Ca2+] by precipitating out a calcium salt. Adding sodium phosphate will yield a Ca3(PO4)2 precipitate, and as the [Ca2+] drops, additional solid CaCl2 will dissolve and yield a higher [Cl] than before (and here Cl– now contributes more to the ion product that it did initially.)