Homework Help: Chemistry

Posted by Sarah on Sunday, February 26, 2012 at 4:05pm.

If very small concentrations of NaCl and AgNO3 are mixed, no precipitate forms. However, if large concentrations are mixed, a white precipitate forms.
Can someone tell me a method for testing the hypothesis that "insoluble" salts would dissolve to some extent in water and are slightly soluble. If the Ksp is low,the solid is not soluble and if high, it is soluble and if it the product of the ion concentration does the exceed the Ksp value, no precipate would form.So thats the hypothesis.So, can someone give me a experiment to test this hypothesis.

Chemistry - DrBob222, Sunday, February 26, 2012 at 4:33pm
I don't think this is something yuo can whip out in a couple of hours. Something along these line might be what you're looking for.

Pick out four or five salts that have varying degrees of solubility. Some examples are AgCl, Ca(OH)2, Fe(OH)3 etc.
You could make saturated solution of each, filter the excess, evaporate the filtrate to dryness and weigh the salt. That way you can show that some salts are more soluble than others.

For the second part, you could make a dilute solution of FeCl3 (quite dilute) and an equally dilute solution of NaOH. Then add one drop NaOH soln to the FeCl3 sol. No ppt if you have the solutions dilute enough. Another drop NaOH. Continue until a ppt starts to form. That way you can show that no ppt forms until the ion-product is exceeded. I picked Fe(OH)3 only because it is easy to see the ppt but the Ksp may be so small (it's in the neighborhood of 10E-36 or so) that it would be difficult to get solutions so dilute that one drop NaOH would not form a ppt. In that case, pick one of the other materials from you list of salts and try again. Remember research isn't something one draws up on paper, writes up, draws conclusions, then performs the experiment. You get an idea, you try it, then redesign to outflank the draw backs, and try again This should get you started.

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