[jools]

Hey guys. I am doing some questions involving the general solubility rules, but I am finding that there are discrepancies between the Genral Solubility Rules Table in my textbook, and the information in my lesson (from a different book). This is what is staed in my lesson:

Let's say that it is required to separate the ions in a solution containing Ag+, Pb2+, and Fe3+ ions. Looking up Ag+ and Pb+ ions, it is seen that both form low solubility compounds with Cl- ions, but that Ag+ ions do not form low solubility compounds with SO4-- ions. Fe3+ ions are soluble in both cases...

Referring to the GSR table in my textbook, rule 3 states:

3. Chlorides, bromides, and iodides are soluble except the silver, mercury(I) and lead compunds. PbCl2 is moderately soluble in hot water.

First off, doesn't that rule contradict itself? It says that lead chloride is not soluble, then states that PbCl2 is moderately soluble in hot water. Also, going back to the exerpt from my text, it states:

"Looking up Ag+ and Pb+ ions, it is seen that both form low solubility compounds with Cl- ions"

Does the rule above not state that silver and lead are not soluble? Am I missing something here, or is my table flawed? Thanks.

[opti384]

We should think about the meaning of "soluble" and "insoluble." By meaning insoluble, it does not mean that totally no amount of that substance is dissolved. Even though it is insoluble, certain minuscule amount is dissolved but only that the rate of precipitation is greater than the rate of dissolution. When we dissolve sugar in water, we see nothing except water. However, in the microscopic level, sugar molecules continuously dissolve and precipitate.

In the case of PbCl₂, I think there's a confusion whether it is insoluble or moderately soluble because it's in the middle of the boundary between the definition of soluble and insoluble substance.