Organic Chemistry and pKa values

[Tawantinsuyu]

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[SnakeOilForSale]

Coffee and some willpower

 

[deleted407021]

Coffee and some willpower

That's about it. Just take about 2 hours a couple days before the test and you should be ok. I hate memorizing but it has to be done when your professor expects it.

 

[Tawantinsuyu]

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[Oso]

I have no advice other than memorize. Make a good playlist, make some flashcards, make an evening out of it. Sorry your teacher sucks (we always got a pKa table on exams).

 

[deleted407021]

I understand memorizing something like functional groups, or symbols for molecules, but I feel like memorizing random digits is impossible

If their being random is a problem, maybe read to understand where they come from. For me, if something seems arbitrary, it is harder to memorize than if it is something with origins that I understand.

 

[darklabel]

Only thing I can say is look for patterns and then repeat what you have to memorize multiple times.

But this crosses the line between difficult teacher and just an ass.

A difficult teacher would feature something on a test that he briefly alluded to (as most do)
But memorizing pKa values is a waste of study time and serves no purpose, especially in Orgo.

 

[Tawantinsuyu]

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[Tawantinsuyu]

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[Pacna]

I think her averages are usually around 40% or 50%

Large curve I assume?

 

[SnakeOilForSale]

I understand memorizing something like functional groups, or symbols for molecules, but I feel like memorizing random digits is impossible

Anything is possible.

When I have to memorize bull**** like that, I just write it over and over a hundred times while saying it out loud. Sure it's annoying but whatever gets the job done right.

 

[Tawantinsuyu]

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[darklabel]

Large curve I assume?

I agree, no classes can fail most of their students, each department usually has a "cap", like no more than >10% of students can fail or at least my school did.

Get a feel for how the other people are doing. If you're below average greater than 1 st. dev., then maybe look into withdrawing.

 

[Tawantinsuyu]

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[Tawantinsuyu]

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[Pacna]

I agree, no classes can fail most of their students, each department usually has a "cap", like no more than >10% of students can fail or at least my school did.

Get a feel for how the other people are doing. If you're below average greater than 1 st. dev., then maybe look into withdrawing.

Not necessarily true. I had a professor who promised that he would not change the class scores; he had a flat grading system. He said that he would fail everyone if people didn't pass the exams and that he would give the office of the registrar the finger if they called him on it. Alternatively, he said he would give everyone a 4.0 if it fell out that way. It turns out the class fell in a normal distribution without a curve, but I believed him.

 

[darksurg]

Lol at memorizing pKa values.

 

[deleted407021]

Lol at memorizing pKa values.

It's ridiculous. We never touched them in ochem I.

 

[Tawantinsuyu]

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[Ace-Co-A]

At least I'll be really prepared for the orgo section of the mcat

No chance. Completely unnecessary for MCAT purposes. A rough idea about pKas (e.g., that carboxylates have a pKa near 4-5 or so) is probably useful intuitively, I guess...

 

[medicalhope]

Maybe figure out in what context she wants them? pKa values can be pretty useful in predicting reactions, so maybe she just wants you to be able to do that? In that case you could just categorize them in ranges, and that would make it way easier to memorize.

If she is expecting you to spit out exact values however, that sucks 🙁. My sympathy.

 

[sat0ri]

I had to do this. Learn how to ball-park them, like carboxylics are ~5 and alcohols what, are like ~1o. It was important in orgo lab and has come up in biochemistry (mechanism/chemistry based, not biology based which most people seem to take), and maybe you'll see that on your MCAT

 

[Tawantinsuyu]

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[ZeaL6]

Are most of you guys forreal that you didnt have to memorize these? lol Its not too difficult really. The only use for them is to predict reactions (especially acid base)

 

[otterxavier]

Does she actually want you to memorize the exact values and be able to do calculations with them, or just to be able to compare the relative pKas of various compounds and predict which way a reaction will go? If it's the latter, it's much easier and more effective to understand the concepts behind pKa (Ka will be higher and pKa will be lower if the conjugate base has a more stable negative charge -- so think about the electronegativity, size, and hybridization of the electron bearing the charge, plus stabilizing effects of resonance and induction, etc.) If it's the former, I'd try to match them up to the tune of a song that you know well.

 

[Entadus]

I understand memorizing something like functional groups, or symbols for molecules, but I feel like memorizing random digits is impossible

They're not random digits. Get a tutor.

(no offense intended. Just some unsolicited advice)

 

[Lord Osis]

I don't see the point "memorizing" pKa, as it varies upon temperature.
Probably "ball-parking" helps, as discussed above.
If the functional group is ionized to give a cation, its pKa must be lower than 7. If it gives an anion, pKa greater than 7.

 

[Entadus]

I don't see the point "memorizing" pKa, as it varies upon temperature.
Probably "ball-parking" helps, as discussed above.
If the functional group is ionized to give a cation, its pKa must be lower than 7. If it gives an anion, pKa greater than 7.

lolwut? The effect of temperature on the equilibrium constant is known: ln(K1/K2) = -delta(H)/R[(1/T2)-(1/T1)]
So we define a standard temperature and memorize the K value (pKa in this case) at these standard conditions. We can then adjust this value accordingly if we run the reaction at a different temperature.

 

[Lord Osis]

lolwut? The effect of temperature on the equilibrium constant is known: ln(K1/K2) = -delta(H)/R[(1/T2)-(1/T1)]
So we define a standard temperature and memorize the K value (pKa in this case) at these standard conditions. We can then adjust this value accordingly if we run the reaction at a different temperature.

That's partly what I'm saying.
pKa values are not absolute universal numbers like the gas constant. These values are exact only within the context of surrounding conditions.
Although the variation in magnitude upon temperature changes may not be drastic, they still are not universal.
To me, memorizing pKa values hardly looks more than memorizing values in steam table at room temperature.

 

[musicalfeet]

I've got a feeling maybe the professor just wants you to be able to ballpark pKas. Also, I found that it's relatively easy to predict pKas if you try to find out why they are around that value.

I don't really see the point in memorizing hard digits....pKas are largely used in predicting which components react with what. As long as you're able to draw from your pKa knowledge base to do that..I don't see why you'd need to know specific values.

I also really think memorizing in ochem is just in general a much harder and tedious way to go...