Compare Solubility of Silver Phosphate in Different Solutions
The dissociation of silver phosphate and solubility product expression is written as follows:
We need to calculate solubility of silver phosphate in different scenarios.
Let x be the solubility in each case.
A. Pure water
This is a straightforward dissolving of silver phosphate to give a saturated solution.
[Ag+] = 3x and [PO43-] = x
We can substitute these into Ksp expression and solve for x.
Solubility x = 4.26 x 10-5
B. 0.10 mol dm-3 AgNO3
AgNO3 will also contribute Ag+ into solution hence Ag+ is the common ion.
Total [Ag+] is approximated to 0.10 mol dm-3 and [PO43-] = x
Substitute into Ksp to solve for x.
Solubility x = 8.89 x 10-14
Notice presence of common ion will suppress solubility. This is also known as the common ion effect.
C. 0.10 mol dm-3 NH3
Ammonia will form diammine silver complex with Ag+.
[Ag+] will decrease and POE for dissociation of Ag3PO4 will shift to the right.
Hence solubility will increase.
D. 0.10 mol dm-3 Na3PO4
Na3PO4 will contribute PO43- into solution so PO43- is the common ion in this case.
[Ag+] = 3x and total [PO43-] is approximated to 0.10 mol dm-3.
Substitute into Ksp to solve for x.
Solubility x = 3.21 x 10-6
Finally we can compare our answers to determine the lowest solubility which is option B.
Topic: Solubility Product, Physical Chemistry, A Level Chemistry, Singapore
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