solubility question

[orangeblossom]

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ugh.. this is such a dumb question, but i can't figure it out.

its from EK gen chem #559.
The question is: Which of the following could change an unsaturated solution of silver chloride into a saturated solution?

It's a I, II, III type question. The answer is all three, which are
I. Lowering the temperature
II. Adding sodium chloride
III. Evaporating some of the water

I thought turning an unsaturated solution into a saturated solution meant that the solubility of AgCl increased? How does lowering the temp increase solubility?? And doesnt adding NaCl reduce solubility due to the common ion effect?

 

[BB8730]

I thought turning an unsaturated solution into a saturated solution meant that the solubility of AgCl increased? How does lowering the temp increase solubility?? And doesnt adding NaCl reduce solubility due to the common ion effect?

Try not to think of it soley in terms of solubility. Decreasing the solubility is one way to saturate the solution but definitely not the only way. Other ways to saturate a solution would be to increase the solute concentration (add a common ion: NaCl) or to decrease the amount of solvent (evaporate water). Lowering the temperature would decrease the solubility, which can also saturate the solution.

 

[LoLCareerGoals]

ugh.. this is such a dumb question, but i can't figure it out.

its from EK gen chem #559.
The question is: Which of the following could change an unsaturated solution of silver chloride into a saturated solution?

It's a I, II, III type question. The answer is all three, which are
I. Lowering the temperature
II. Adding sodium chloride
III. Evaporating some of the water

I thought turning an unsaturated solution into a saturated solution meant that the solubility of AgCl increased? How does lowering the temp increase solubility?? And doesnt adding NaCl reduce solubility due to the common ion effect?

No. It is the opposite. Saturated = concentration is @ solubility limit.
Unsaturated = concentration < solubility limit.
Supersaturated = concentration > solubility limit.
Currently we are in #2 situation. So we either need to bring concentration up or bring solubility down to turn < into =:
I. Brings solubility down. Check
II. Brings solubility down (common ion effect). Check.
III. Brings concentration up (same amount of solute/less solvent volume). Check.

Also can you please not post answers or at least post them in white? Give people a chance to practice and make their own errors. Once you get a few answers, then post the book's.

 

[orangeblossom]

Oh ok. Sorry for posting the answer. Thanks for the explanations, both of you! I'm really bad at chem 🙂

 

[sports]

I am wondering how the solubility rules factor into this? I remember that silver is not soluble except for in its perchlorate, nitrate or acetate form.

 

[LoLCareerGoals]

Solubility is not a binary concept. Those compounds that are referred to as soluble simply have high or effectively infinite solubility. Those that are insoluble, have low solubilities.