Organic Chemistry Question

[E. coli]

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Here is one of the DAT achiever question:

Which of the following description(s) is/are NOT true pertaining to the acid-base characteristics of glycine, H2NCH2CO2H?

I. Insoluble in water
II. One mole of base is sufficient to fully deprotonate one mole of glycine
III. Predominantly zwitterion at isoelectric pH

A- I only
B- II only
C- I and II only
D- II and III only
E- I and II and III

I was just wondering if glycine is water soluble or insoluble. Glycine has a nonpolar neutral R group (H), so wouldn't it be water insoluble? I am getting confused because the answer says glycine is water soluble.

 

[dat_student]

Here is one of the DAT achiever question:

Which of the following description(s) is/are NOT true pertaining to the acid-base characteristics of glycine, H2NCH2CO2H?

I. Insoluble in water
II. One mole of base is sufficient to fully deprotonate one mole of glycine
III. Predominantly zwitterion at isoelectric pH

A- I only
B- II only
C- I and II only
D- II and III only
E- I and II and III

I was just wondering if glycine is water soluble or insoluble. Glycine has a nonpolar neutral R group (H), so wouldn't it be water insoluble? I am getting confused because the answer says glycine is water soluble.

I'd say A eventhough other people may say C. You only have one acidic H that can be deprotonated by the OH base. ;-) It depends on the pH of the solution too (acidid, basic, or isoelectric pH?!) You have to make some assumptions.

Watch out ! Their O'Chem 2 test has a couple of questions that have 2 right answers. I had to guess which of the two equally correct answers is the right answer. ADA-sample test is the only test free of errors. All other tests have a bunch of errors (TopScore, DAT Achiever, even Kaplan). So, be careful...

 

[elz787]

which ones in kaplan?

 

[lcinva]

I'd say A eventhough other people may say C. You only have one acidic H that can be deprotonated by the OH base. ;-) It depends on the pH of the solution too (acidid, basic, or isoelectric pH?!) You have to make some assumptions.

Watch out ! Their O'Chem 2 test has a couple of questions that have 2 right answers. I had to guess which of the two equally correct answers is the right answer. ADA-sample test is the only test free of errors. All other tests have a bunch of errors (TopScore, DAT Achiever, even Kaplan). So, be careful...

yeah I would say A, because glycine should be fully deprotonated by one mole...my question is, why is glycine water soluble then? It is non-polar, so I'd think it would be correct to say that its insoluble...

 

[Audio]

Glycine is soluble because it's so small and because it can H bond.

My questions is this...are we assuming physiological pH? Is that why only one mole of base is needed?

 

[dat_student]

Glycine is soluble because it's so small and because it can H bond.

My questions is this...are we assuming physiological pH? Is that why only one mole of base is needed?

lol we have to assume something. The question doesn't give me much info. I assumed the pH of the environment has no effect on this molecule:H2NCH2CO2H 😉

 

[Mustt Mustt]

I am taking my DAT tomorrow and will let you know of my personal experience.

I have personally found DAt Acheiver useless for Science section but it is really good in RC,PAT and I don;t know about QR becasue I don;t have time to go over that. I think it is uselss iun science sections becasue it is insanely hard compare to real deal. Personally I would only use Kaplan BB and TS unelss you need extra practice in PAT which I needed. I think all theses new materials are confusing students even more and doesn't give the test taker the idea of real test.

 

[seoul]

Here is one of the DAT achiever question:

Which of the following description(s) is/are NOT true pertaining to the acid-base characteristics of glycine, H2NCH2CO2H?

I. Insoluble in water
II. One mole of base is sufficient to fully deprotonate one mole of glycine
III. Predominantly zwitterion at isoelectric pH

A- I only
B- II only
C- I and II only
D- II and III only
E- I and II and III

I was just wondering if glycine is water soluble or insoluble. Glycine has a nonpolar neutral R group (H), so wouldn't it be water insoluble? I am getting confused because the answer says glycine is water soluble.

As you might have already noted, there's actually no R group here since the only element present there at the side chain is H. Solubilty of glycine in water is mainly attributable to the its stable zwitterion (dipolar ion) form, making solvation from water molecules easily accomplished. In fact, if you were to put a small sample of glycine into a nonpolar organic solvent, it would remain insoluble there.

As pointed out by dat_student, glycine in statement II should have been described as being present in strong acid to depict the neccessity of having two moles of base to titrate the polyprotic acid described by the author in the answer solution page. Otherwise, it can easily be misinterpreted as the emergence/presence of zwitterion in its stable form needing only one equivalent of base to be deprotonated with.