TBR: Glutamic Acid is Triprotic???

[justadream]

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Why is glutamic acid triprotic in water?

Isn't the "protic" number (monoprotic/diprotic/triprotic) determined by the # of moles of "things" formed when the bigger molecule dissociates?

Although glutamic acid has the ability to lose 3 protons, in water, shouldn't it only lose 2 (the COOH and the side-chain which has pka = 4.3)?

This is from TBR GC I page 279 #90

 

[Sammy1024]

The protic number is determined by exactly what you said, which is losing the number of protons. It can technically lose 3 protons so it is triprotic. In real life it may not do that.

It can lose one from the left OH, one from NH2 and the third from the OH on the right, so triprotic. If it didn't have a second OH then it would be diprotic.

 

[justadream]

@Sammy1024

But the question says IN WATER.

Are you saying that when determining the protic number, just disregard the solvent?

 

[Sammy1024]

Yupp. When you determine the protoc number in general chemistry you don't even have a solvent. But you can still determine the number. Solvent is not necessary to figure it out so you ignore it.

If the questions asks specifically what kind of rxn you expect in this solvent then you would consider it.