please help explain #59 on AAMC7_supersaturation

[mcat_study]

In question # 59 of the AAMC7,
why is the answer
a saturated solution with 1.3g of undissolved salt instead of supersaturated solution (answer D). I looked up a definition of a supersaturated solution on wiki and in my mind, it describes exactly what the questions stem is asking. maybe the key is that it was left over for several days and the solute adsorbed to a crack or got nucleated?
please help
thank you

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[ChymeChancellor]

In question # 59 of the AAMC7,
why is the answer
a saturated solution with 1.3g of undissolved salt instead of supersaturated solution (answer D). I looked up a definition of a supersaturated solution on wiki and in my mind, it describes exactly what the questions stem is asking. maybe the key is that it was left over for several days and the solute adsorbed to a crack or got nucleated?
please help
thank you

You're discussing specific problems. Qof Quimica will lay the smack down on you.

 

[gridiron]

You're discussing specific problems. Qof Quimica will lay the smack down on you.

 

[mcat_study]

You're discussing specific problems. Qof Quimica will lay the smack down on you.

what?
sorry, but this is an officially released exam, and i did not write up the whole question stem.
so please someone help
it is actually the concept of supersaturation that i am asking about.
i really don;t know how else to ask this question?

 

[GeoMay22]

A supersaturated solution is a solution containing more dissolved solid than the liquid would normally dissolve. These solutions are made by heating the liquid when the solid is being added and when the solution cools there is no precipitation. Remember that temperature can change the equilibrium of the reaction, which allows the solubility to change also.
This particular solution that you are asking about is never able to become supersaturated because the temperature remains at a constant 0 C. Initially when the solid is added the forward (dissolution) reaction is faster than the reverse (precipitation) reaction, but once the solubility amount of solid has been dissolved the reaction reaches equilibrium. This means the forward and reverse reactions proceed at the same rate. For this reason, there is excess solid left over that cannot be dissolved.

 

[mcat_study]

A supersaturated solution is a solution containing more dissolved solid than the liquid would normally dissolve. These solutions are made by heating the liquid when the solid is being added and when the solution cools there is no precipitation. Remember that temperature can change the equilibrium of the reaction, which allows the solubility to change also.
This particular solution that you are asking about is never able to become supersaturated because the temperature remains at a constant 0 C. Initially when the solid is added the forward (dissolution) reaction is faster than the reverse (precipitation) reaction, but once the solubility amount of solid has been dissolved the reaction reaches equilibrium. This means the forward and reverse reactions proceed at the same rate. For this reason, there is excess solid left over that cannot be dissolved.

I really appreciate your help
thank you very much for a clear response

 

[QofQuimica]

You're discussing specific problems. Qof Quimica will lay the smack down on you.

It's fine to discuss general topics from the tests; however, please don't post actual AAMC test questions or answers on SDN. The AAMC monitors this site, and we aren't allowed to do that. That even goes for their practice tests.

Also, mcat_study, please only post your question once, in one forum. Multiple identical threads in different forums are not permitted on SDN. If you are not sure which forum is the appropriate one to post your question, ask one of us; we're glad to help.

 

[MSc44]

It's fine to discuss general topics from the tests; however, please don't post actual AAMC test questions or answers on SDN. The AAMC monitors this site, and we aren't allowed to do that. That even goes for their practice tests.

Also, mcat_study, please only post your question once, in one forum. Multiple identical threads in different forums are not permitted on SDN. If you are not sure which forum is the appropriate one to post your question, ask one of us; we're glad to help.

thats strange, is aamc agnst students helping eachother out!???

 

[QofQuimica]

thats strange, is aamc agnst students helping eachother out!???

No. The AAMC is against people violating their copyrights.

 

[xanthomondo]

thats strange, is aamc agnst students helping eachother out!???

not that exactly, theyre just petrified that they won't rake in every penny thats remotely possible

 

[mcat_study]

No. The AAMC is against people violating their copyrights.

I do admit that quoting AAMC is a bad idea from a legal standpoint although arguable.
I just feel really bad, because i spent all this money buying their expensive exams and explanations, only to find out that their explanations are less than mediocre. in science explanation sections, AAMC only addresses the correct answers without going into the wrong choices. thus students cannot fully grasp the problem, the root of the problem, which makes most of their explanations useless.

i realize that they want to weed people out, but why is it a violation of their copyrights to address something they failed to cover in their explanations?

sorry i am just venting. i understand QofQuimca, and will comply with the rules of this website/forum

 

[QofQuimica]

I do admit that quoting AAMC is a bad idea from a legal standpoint although arguable.
I just feel really bad, because i spent all this money buying their expensive exams and explanations, only to find out that their explanations are less than mediocre. in science explanation sections, AAMC only addresses the correct answers without going into the wrong choices. thus students cannot fully grasp the problem, the root of the problem, which makes most of their explanations useless.

i realize that they want to weed people out, but why is it a violation of their copyrights to address something they failed to cover in their explanations?

sorry i am just venting. i understand QofQuimca, and will comply with the rules of this website/forum

It's ok; I've gone through this whole process too, and I could help you write the book about how frustrating it is. It's just that the AAMC monitors SDN, so we have to remove their test questions whenever people post them.

Just to be clear, the main constraint is that you cannot post specific questions. It's fine though to ask about general topics, like you did about salt solubility. So if you read an explanation that you don't understand, just post your question about that topic in general. And try not to let the MCAT get to you too much.