Question

Which of the following phosphate salts is most soluble in pure water? a. Sr3(PO4)2; Ksp - 1.0 x 10-31 26. Ag3PO4: Ksp = 8.9 x 10-17 CPb3(PO4)2; Ksp = 1.0 x 10-54 d. Ba3(PO4)2: Ksp = 6.0 x 10-39 e. Cu3(PO4)2; Ksp - 1.4 x 10-3

Answer 1

Correct option is : (b.) Ag3PO4 ; Ksp = 8.9 x 10-17

Explanation

The most soluble compound will have the largest Ksp value.

Out of the given choices we see that Ag3PO4 and Sr3(PO4)2 have large Ksp values.

Let us find the dissolved concentrations of both salts

When Sr3(PO4)2 dissolves in pure water, we get 3 ions of Sr2+ and 2 ions of PO4 3- per molecule which dissolves.

Ksp Sr3(PO4)2 = [Sr2+]3[PO4 3-]2

1.0 x 10-31 = (3s)3 * (2s)2

where s = dissolved concentration of salt

1.0 x 10-31 = 108s^5

s^5 = (1.0 x 10-31) / 108

s^5 = 9.26 x 10-34

s = (9.26 x 10-34)^(1/5)

s = 2.5 x 10-7 M

When Ag3PO4 dissolves in pure water, we get 3 ions of Ag+ and 1 ion of PO4 3- per molecule which dissolves.

Ksp Ag3PO4 = [Ag+]3[PO4 3-]

8.9 x 10-17 = (3s)3 * (s)

where s = dissolved concentration of salt

8.9 x 10-17 = 27s^4

s^4 = (8.9 x 10-17) / 27

s^4 = 3.3 x 10-18

s = (3.3 x 10-18)^(1/4)

s = 4.3 x 10-5 M

Since concentration of Ag3PO4 > concentration of Sr3(PO4)2, therefore, Ag3PO4 is the most soluble salt among the given options.