A solution contains 0.0440 M Ca2 and 0.0940 M Ag. If solid Na3PO4 is added to this mixture, which of the phosphate species would precipitate out of solution first? A. Na3PO4.
B. Ag3PO4.
C. Ca3(PO4)2
When the second cation just starts to precipitate, what percentage of the first cation remains in solution?

C.  will precipitate out first

the percentage of remaining =  12.86%

Explanation:

Given that:

A solution contains:

From the list of options , Let find the dissociation of

where;

Solubility product constant Ksp of is

Thus;

replacing the known values in order to determine the unknown ; we have :

The dissociation  of

The solubility product constant of  is

The dissociation of   is :

Thus;

Thus; the phosphate anion needed for precipitation is smaller i.e in than  in    

Therefore:

 will precipitate out first

To determine the concentration of when  the second cation starts to precipitate ; we have :

This implies that when the second  cation starts to precipitate ; the  concentration of in the solution is  0.00566

Therefore;

the percentage of  remaining = concentration remaining/initial concentration × 100%

the percentage of remaining = 0.00566/0.0440  × 100%

the percentage of remaining = 0.1286 × 100%

the percentage of remaining =  12.86%

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