AAMC FL 3 C/P #16 & 18

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newensj
Posts: 6
Joined: Thu Aug 01, 2019 11:49 pm

AAMC FL 3 C/P #16 & 18

Post by newensj » Sun Aug 25, 2019 2:14 pm

Hello! Sorry if these questions has been asked before but I cannot seem to find it.

I was wondering why AAMC FL3 C/P #16 is redox instead of precipitate formation?
I know the redox potentials were given, but how would we be able to tell if they didn't give us the redox potentials, especially since there was a precipitate that formed?

Also, for C/P #18, I thought a period would be the time it goes up AND down. For example, in a sin graph, the amplitude goes + and then - and that counts as one period. That's why I chose 1500 ns because the absolute value of a - would show up in the positive region.
sorry if this question is confusing! but basically I'm wondering if the definition of period is always the "shortest repetition time" or if, like in an absolute value of a sin graph like this picture[https://i.stack.imgur.com/KiP15.png])

Thanks in advance!
NS_Tutor_Mathias
Posts: 280
Joined: Sat Mar 30, 2019 8:39 pm

Re: AAMC FL 3 C/P #16 & 18

Post by NS_Tutor_Mathias » Mon Aug 26, 2019 12:02 pm

#16:
I2 and zinc aren't precipitating together - a precipitate is formed, but NOT between these two. Of the two species the question asks about, one is oxidized and the other reduced. Without the reduction potentials, you would need to be provided a chemical equation (from which assigning oxidation states is trivial) or at the very worst infer the properties of each species from the periodic table (unlikely that the MCAT would want you to do this, since it is not a particularly reliable approach).

#18:
You're not quite wrong in your explanation here, but your application of these principles to a square wave seems to have a few flaws. Periodicity generally is the time it takes to fully repeat a cycle of any process. In this case, after 500 ns of 6 kV voltage between electrodes and 500 ns of 0 kV, we are back where we started.

You can apply this principle to any wave too: Take a regular, continuous sine wave and pick any point on it. Find the next time this exact point with the exact same neighboring points occurs and the distance between those two is a period. A small amount of confusion arises that for any such point EXCEPT the peaks and troughs, there will be one instance in which the y value of the sine function is identical but the neighboring points are not identical - the distance between two such points is a half-period.
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