Predicting Precipitates: Solubility Rules for Cations and Anions

[ACLerok]

I'm taking Chem II over the summer at a junior college and was given this problem on one of my homework assignments:

I am told I have a sol'n containing the cations Ag, Al, As, Ba, Bi, Ca, Cd, Co, Cr, Cu, and Fe.

My objective is to write all the compounds that would be precipitated if hydrochloric acid is added to the above sol'n.

My instincts are telling me to just use the solubility rules. For example, when Ag and hydrochloric acid combine, AgCl is formed but according to the solubility rules AgCl is insoluble so AgCl would be one of the compounds that would be precipitated. Am I going about this all wrong or what? Thanks alot!

 

[Bystander]

You're doing fine.

 

[ACLerok]

The 2nd part says that a reagent is now needed that will precipitate the smallest number of remaining cations and that the best reagent for this is hydrogen sulfide plus hydrochloric acid. It then asks me to find all the compounds that would be precipitated.

Do I just go about this the same way for the first part? I don't understand when they say 'smallest number of cations'. Please can anyone help me with this?

 

[Bystander]

Same game. You've knocked out the silver. Now, you want to know what else is in there, and you'd like to find out one, or at most a few at a time. By "smallest number," they mean the smallest number of different species, rather than the smallest total amount of ions precipitated from solution. Pretty ambiguously written.

 

[ACLerok]

for the first part, the only compound I got is AgCl and for the second part I got AsS, BiS, CdS, and CuS.

Am I right on this ones or no? And thanks a lot for all your help.

 

[Bystander]

Looks 'bout right.

 

[GCT]

In your chemistry textbook should be a list of insoluble and soluble ionic compounds, just correspond with this table, shouldn't take too long.


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[Rampantbaboon]

i don't know how deep into this you are going, but this seems like a trick question from my experience. there was a given amount of HCl and you had to see how much of what compound would form by using the solubility product. although if you havnt touched on that stuff yet i'd be certain your on the right path