Can I ask this here?

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Flower_Child

Flower_Child

Full Member
7+ Year Member
How do you find the pH of an amino acid. I don't get it. I have googled everything and can't find anything on khan academy. and I've read my book and am still wanting to rip my hair out. Sorry if this isn't the place. But I don't understand ( when it comes to titration) how they get the curve with the pH. I get everything else, I just don't get that.
 
Are you talking about the two curves for the two functional groups? Oh wait, is this a homework problem?
 
There is no such thing as the pH of an amino acid. There are pKa's for the functional groups on the amino acid, and there is a pI for the amino acid as whole. The pKa of a functional group on an amino acid is the pH at which that particular functional group is 50% protonated and 50% deprotonated. You can find it on a titration curve by going to the vertical inflection point, look at the volume of titrant added and going to half of that volume. The y-value (pH) for that volume on the titration curve is called the pKa
 
Flower_Child said:
Okay first off... I want to know how you did that lol. and yeah I clicked on a few of those links. But I am still not sure where the pH on the left side is coming from. I don't know how to explain myself and i can't figure out how to post a picture
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Glad you took that with a sense of humor 🙂 Google "let me google that for you", type in your search, and it generates the link you can post. it's my favorite way to be passive-aggressive.

to your original question, post an example problem of what exactly you're looking for. Just write it?
 
New_Slang said:
Glad you took that with a sense of humor 🙂 Google "let me google that for you", type in your search, and it generates the link you can post. it's my favorite way to be passive-aggressive.

to your original question, post an example problem of what exactly you're looking for. Just write it?
Click to expand...
I just don't understand the pH on the left side, where is this coming from! Its driving me nuts, because I keep watching tutorial videos, and none of them explain that. Its just like assumed you know. and every graph i look at it seems it has the same pH. Maybe its from my lack of sleep, but its driving me crazy.
 
Flower_Child said:
Okay first off... I want to know how you did that lol. and yeah I clicked on a few of those links. But I am still not sure where the pH on the left side is coming from. I don't know how to explain myself and i can't figure out how to post a picture
Click to expand...
As you add titrant (strong acid or base), the pH will change
 
So I have a new question if someone can answer it. Do you just have to memorize the pka of amino acids? Is there like a logical way where I don't have to memorize the pkas. From what I understand, knowing the pka is the only way to do titration problems.
 
Here is what I am doing. The pka, is that just a tedious thing that needs memorizing? Or is there a logical reasoning for it. It just feels random.
 

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If you're given a titration curve, you should be able to read the pKas right off of the curve. For amino acids, just know that amino group is around 9ish and carboxy is around 2ish. After that just memorize the side chain pKas for the AAs that have ionizable side chains
 
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