Question

Which of the following compounds, when added to a 1.0-M solution of HClO₄, has a solubility greater than in pure water? Select all that apply.

Group of answer choices

Cr(ClO₄)₃

Ca₃(PO₄)₂

PbI₂

ZnS

AgBr

BaF₂

Answer 1

1-

Cr(ClO4)3 dissociate in water as-

Cr(ClO4)3 -----------> Cr+3 + 3(ClO4)-

Now when we add HClO4 to this solution, we know HClO4 also dissociate in water as-

HClO4 -----------> H+ + (ClO4)-

That means after addition of HClO4, the concentration of (ClO4)- in the solution will increase. That means the recation

Cr(ClO4)3 -----------> Cr+3 + 3(ClO4)-

will strat proceeding in backward direction i.e formation of Cr(ClO4)3 from Cr+3 and (ClO4)-

So the solubility of Cr(ClO4)3 will decrease upon addition of HClO4

2-

Ca3(PO4)2 dissociate in water as-

Ca3(PO4)2 -----------> 3Ca+2 + 2(PO4)-2

Now we know (PO4)-2 is the conjugate base of the weak acid H3PO4. Now weaker the acid, stronger is its conjugate base. So we can say (PO4)-2 is a strong base which can realdily accept H+ from HClO4 to gete converted to H3PO4

In this way the amount of (PO4)-2 froom the solution will decrease.

So according to Li-chatelier's principle, the reaction Ca3(PO4)2 -----------> 3Ca+2 + 2(PO4)-2 proceed in forward direction to produce more ions

So more Ca3(PO4)2 will dissolve in water

So the solubility of Ca3(PO4)2 will increase.

3-

PbI2 dissociate in water as-

PbI2 -----------> Pb+2 + 2I-

when we add HClO4 to this solution, these is no common on between them. So addition of HClO4 will have no effect on the solubility of PbI2.

Again I- is the coonuugate base of a strong acid HI. So adding strong acid won't affect the solubility of PbI2

4-

ZnS sparigngly dissociate in water as-

ZnS -----------> Zn+2 + S-2 to a very less extent.

In this case when we add a strong acid like HClO4, then the net pH of the solution dereases due to addition of a strong acid.

So adding a strong acid increases the solubility of the salt.

Because we know S-2 is the conjugate base of the weak base H2S. Now weaker the acid, stronger is its conjugate base. So we can say S-2 is a strng base which can realdily accept H+ from HClO4 to gete converted to H2S

In this way the amount of S-2 froom the solution will decrease.

So according to Li-chatelier's principle, the reaction ZnS -----------> Zn+2 + S-2 proceed in forward direction to produce more ions

So more ZnS will dissolve in water

So the solubility of ZnS will increase.

5-

AgBr dissociate in water as-

AgBr -----------> Ag+ + Br-

when we add HClO4 to this solution, these is no common on between them. So addition of HClO4 will have no effect on the solubility of AgBr.

Again Br- is the coonuugate base of a strong acid HBr. So adding strong acid won't affect the solubility of AgBr

6-

BaF dissociate in water as-

BaF -----------> Ba+2 + F-

Now F- is a strong conjugate base of weak acid HF. So adding another strong acid HClO4 increases the solubility of BaF