gen chem help please!

[yellowstar]

Hello SDN!
This is my first post, and it is about gen chem questions (I have a few). I would appreciate any help!

(These are all from Kaplan's full length test #1)

1) One problem says that a reaction of AgNO3 and Na2SO4 in water goes to completion because "silver sulfate quickly precipitates."

But isn't Ag2SO4 soluble? Not insoluble?

2) How many moles of electrons does it require to liberate gold from AuC? The explanation says 1 mole, but does that mean that C has a charge of -1, and Au a charge of +1?

3) In a list of salts with corresponding Ksp values, PbBr2 has the highest Ksp value, and thus, the answer says that it is the most soluble in water, and that it would result in the lowest freezing point of a saturated aqueous solution.

But isn't PbBr2 insoluble? The other salts were: Cd(CN)2, CrPO4, and CuCN (all with lower Ksp values than that of PbBr2). I'm just getting confused because I understand the explanation in terms of Ksp, but this conflicts with the solubility rules from Kaplan's book....

Please help! Thank you!

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[Danny289]

don't confuse solubelity and reactivity.

 

[gentile1225]

One problem says that a reaction of AgNO3 and Na2SO4 in water goes to completion because "silver sulfate quickly precipitates."

But isn't Ag2SO4 soluble? Not insoluble?

>>> Group one elements, such as Na, easily dissolve in water. Ag and Pb are common elements that will form precipitates.

i'll work on the other ones, i need a nap first though, too tired right now.

 

[yellowstar]

Thanks guys!
Hopefully I can understand it soon.