Thursday, April 14, 2011
Chemistry AP Questions: AP Exam Review
Post your questions below. Be specific; don't just ask for a solution (you have access to all of those), rather ask questions like "how would you know to..." or "can I do it this way...". I will post a video response with a white board from my dining room on Friday.
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Should I say "this is B from AP Chem" or just give my whole name? Anyway, I was doing the Sparknotes practice MC and I had trouble with this question:
----------SPOILER ALERT----------
33. The addition of an oxidizing agent such as bromine water to a clear solution of an unknown compound results in a color change. When this solution is shaken with an equal volume of mineral oil, the mineral oil layer turns purple. The unknown compound probably contains
(A) Cl–
(B) Br–
(C) MnO4–
(D) I–
(E) Co2+
The correct answer was D. I read over their explanation, but 1. I thought I- was red-brown rather than purple 2. How would we know that it's not C and 3. They say E can't react with Bromine, but why can't it form CoBr2?
I think CoBr2 would still be aqueous, so there would be no net ionic reaction in E. Molecular Iodine, I2, can be the reddish brown that you are referring to, and iodide, I- is not colored. Triodide ion (I3-) is purplish, and in this case the iodine has been oxidized from -1 to -1/3. I would say that this is a fact to know, but who knows, perhaps knowing that fact may come up on your exam.
This is A from AP Chem.
In the AP Chemistry open response section, I was a bit confused on one question. It asked which salt has the greater Ksp value: AgBr or AgI? The answer according to their description of the reaction is AgBr, and the explanation is logical too. However, I was confused because I thought this was contrarty to what we learned in the Ksp lab, since our ultimate conclusion was that solubility increases as we go down a group in the periodic table (more shells,greater distance to nucleus,easier to ionize,etc). So in that case, why doesn't AgI have a higher Ksp?
I think in this case, it has more to do with the solvation enthalpies. The halogens get LESS soluble as you move down in within the group, as opposed to the trend observed with the alkali earth metals. The take home message should be that the same properties don't always apply to all elements in all groups on the periodic table.
This is A from AP Chemistry. Where exactly will the AP exam take place?
To be announced when we get back. Last year it was held in the library.
I remembered correctly and we don't have all the solutions or I would/ should have done my HW :D
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