[antoinetta]

Ok I supposed to rank the following five salts in order of decreasing solubility, in terms of mass per unit volume.
(ie The most soluble gets rank 1, the least soluble gets rank 5.)

Ba₃(PO₄₎₂ (Ksp = 6.00 × 10^?39)
Ca₅(PO₄)₃OH (Ksp = 6.80 × 10^?37)
AgI (Ksp = 1.50 × 10^?16)
Ag₃PO₄ (Ksp = 1.80 × 10^?18)
PbBr₂ (Ksp = 4.60 × 10^?6)

So, I figure out the concentration, denoted as s,  of each of the following:

Ba₃(PO₄₎₂ (s = 8.89 × 10^?9))
Ca₅(PO₄)₃OH (s = 2.720 × 10^?5)
AgI (s = 2.72 × 10^?5)
Ag₃PO₄ (s = 1.22 × 10^?8)
PbBr₂ (s = 1.05 × 10^?2)

Then, converted it to g/L by multiplying s and the molecular weight:

Ba₃(PO₄₎₂ (solubility = 5.34 × 10^?6))
Ca₅(PO₄)₃OH (solubility = 1.36 × 10^?2)
AgI (solubility = 2.88 × 10^?6)
Ag₃PO₄ (solubility = 6.73 × 10^?3)
PbBr₂ (solubility = 3.845)

So, by ranking them:

1) PbBr₂
2) Ca₅(PO₄)₃OH
3) Ag₃PO₄
4) AgI
5) Ba₃(PO₄₎₂

Is this correct?  I would appreciate any input.

[Borek]

Something is wrong. For AgI concentration listed is off by three orders of magnitude, yet solubility in g/L is OK.

Unless AgI solubility is given for Ag₃PO₄... But then I can't find correct solubility of PbBr₂.

Show how you did Ba₃(PO₄)₂.

[antoinetta]

Show how you did Ba₃(PO₄)₂.

Ba₃(PO₄)₂ <--> 3 Ba²⁺ (aq) + 2 PO₄^3- (aq)

Ksp = [Ba2+]³ * [PO43-]²  = 6.00 × 10^?39

(3s)³ x (2s)² = 6.00 × 10^?39

s = 8.89 × 10^?9 mol/L

solubility = 8.89 × 10^?9 x (601 g/mol) = 5.34 × 10^?6 g/L

[Borek]

Approach is OK, so perhaps AgI problem was just a typo. PbBr₂ solubility is OK, my mistake.

[antoinetta]

I don't know if my answer is correct though