pH

[sam0001]

How do we draw amono acids at a pH of 6? In their zwitterion form ( assuming they have no acid or base groups on their side chain) or in their charged form?

[thushan]

How do we draw amono acids at a pH of 6? In their zwitterion form ( assuming they have no acid or base groups on their side chain) or in their charged form?

what is the question? you'd need to know the pKa values of each of the amino and carboxy groups. they shouldn't really ask that qn.
but i have a feeling that the carboy groups are deprotonated and the amino group protonated at pH 6.

[sam0001]

Question was, draw Alanine ata pH of 6

[thushan]

Question was, draw Alanine ata pH of 6

Yeah, they shouldn't ask that question in a unit 3 exam. But as a general rule, pH < 1 means everything protonated, pH > 12 means everything deprotonated.

[charmanderp]

According to a Google search, alanine's isoelectric point is at a pH of 6.0. Would that mean it's in its zwitterion form at that stage?

[Destiny]

Yes.

[sam0001]

For vces sake,how would we write it though? That's what I'm confused about.

[charmanderp]

H3N+CH(Z)COO^-. You should have learnt that in class by now.

[sam0001]

Lol, we just started area of study two actually.

[sam0001]

And I meant at a ph of 6? Do we treat it as though it's in an acidic solution?

[Destiny]

Oh lord. Finish the entire course by yourself, the exam's in less than 1 month.
EDIT: sam, treat it like it's an acidic solution UNLESS they state the isolelectric point in the question; my teacher says the isolelectric point is outside the course.

[ligands]

i had a question very similar to this today but it was Alanine at ph-11 i didn't know what to draw haha perhaps i should go over organic chem -.-

[Destiny]

Just go over the bit in the book, and look, cover, draw, check until you can remember them   There's no special way to learning the Zwitterions and the acid/base forms, it's mainly just rote learning.

[thushan]

Just go over the bit in the book, and look, cover, draw, check until you can remember them   There's no special way to learning the Zwitterions and the acid/base forms, it's mainly just rote learning.

Hold on - I really doubt VCAA expects you to know pKa values (which determine which form the amino acid is in at a certain pH), it's not in VCAA Chemistry's nature to memorise random bits of information - hence the use of the Data Book.

The only VCAA questions I've seen that have that kind of qn has pH either 1 or 7 or 14. They're reasonable.

[ligands]

i had the data book just nothing was happening haha i don't think we covered pKa values yet