Suppose you have a solution that contains 0.0450 M Ca2 and 0.0930 M Ag . If soli

Question

Suppose you have a solution that contains 0.0450 M Ca2 and 0.0930 M Ag . If solid Na3PO4 is added to this mixture, which of the following phosphate species would precipitate out of solution first?

When the second cation just starts to precipitate, what percentage of the first cation remains in solution?

Map Sapling Learning macmillan learning Suppose you have a solution that contains 0.0450 M Ca2 and 0.0930 M Agt. If solid Na3PO4 is added to this mixture, which of the following phosphate species would precipitate out of solution first? O Cas(PO4)2 Na3PO4 When the second cation just starts to precipitate, what percentage of the first cation remains in solution? Number PreviousGive Up & View SolutionCheck AnswerNextExit

Explanation / Answer

The Ksp of calcium phosphate is 2.07x 10-33 and that of silver phosphate is 8.87x 10-17

To know which of these two precipitates first , let us calculate the [PO4-3] in each case.

i) Ca3(PO4)2   <-----> 3Ca+2 + 2PO4-3

Thus Ksp = [Ca+2]3[PO4]2

Given [Ca+2] = 0.0450M

Thus [PO4]2 = 2.07x 10-33 /(0.045)3

Thus phosphate concentration required = 4.868x 10-15 M

ii) Ag3PO4 <-----> 3Ag+   + PO4-3

Thus Ksp = [Ag+]3[PO4]

Thus 8.87x 10-17 = (0.0930)3[PO4]

[PO4] = 1.1x 10-13M

Since calcium phosphate requires lower concentratio of phosphate , it only precipitates first.

Q2)

When the second cation, Ag+ starts precipitation, the amount of first cation remaining is given by

[Ca+2] /{Ag+] = Ksp of calcium phosphate / kasp of silver phosphate

= 2.07x10-33 /8.87x10-17

   = 2.334x10-17

% of it = 2.334 x10-15  M

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