pH

[thushan]

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

Oh no my point is that VCAA is not going to ask you to draw amino acids at dodgy pH values like 3 - 10 because that requires knowledge of pKa values which are not in the Data Book and VCAA shouldn't expect you to memorise this.

If they do though somehow, let us know on ATARnotes and I'll email my chem teacher (who is an assessor) and tell her to complain to chief examiner (who has the power to scrap short answer questions).

[Mao]

Carboxylic acids tend to have pKa ~ 4. Amines tend to have pKa ~9. So if we are working in the range of pH=6~8, we can pretty safely assume it'll be in its neutral zwitterion state. (and any side-group acid/bases will also have a charge).

[thushan]

Carboxylic acids tend to have pKa ~ 4. Amines tend to have pKa ~9. So if we are working in the range of pH=6~8, we can pretty safely assume it'll be in its neutral zwitterion state. (and any side-group acid/bases will also have a charge).

Hmm, in amino acids I think the carboxy group has a pKa of closer to 2.

[Mao]

Carboxylic acids tend to have pKa ~ 4. Amines tend to have pKa ~9. So if we are working in the range of pH=6~8, we can pretty safely assume it'll be in its neutral zwitterion state. (and any side-group acid/bases will also have a charge).

Hmm, in amino acids I think the carboxy group has a pKa of closer to 2.

Carboxyl on side chains have pKa ~ 4. So generally, at pH = 6~8, we can safely assume all carboxyl groups are deprotonated.

Similar argument for the amine group.