Which of the following forms of aspartic acid would you expect to predominate at low pH, neutral pH, and high pH?
a.
b.
c.

Question

Which of the following forms of aspartic acid would you expect to predominate at low pH, neutral pH, and high pH?

a.

b.

c.

Accepted Answer

Hi, everyone. Let's take a look at our next problem. It says the different forms of glutamic acid pi 3.2 are shown below, determine which form primarily exists at low ph neutral ph and high ph. Our answer choices are a number one, primarily at low ph. Number two, primarily at high ph. Number three, primarily at high ph choice B. Number one, I'm just going to read the PH. So it's not so long. Number one, high ph number two low ph. Number three low ph choice C number one, high ph, number two low ph, number three, neutral ph and choice D number one, neutral ph number two, high ph, number three, high, low ph, excuse me. So note that in our answer choices, we don't have to have low, neutral and high for these three forms. So we may have more than these three forms and perhaps we have none at neutral ph, for instance, as some of our answer choices, say, so keep that in mind when thinking through this. So let's look at molecule number one. So we want to look for the charges on here for our different forms. So in this case, our molecule has two carboxylic acid groups. One is the one in the backbone. I'm gonna go ahead and highlight the R group so I can keep straight the backbone carboxylic acid from the R group. So I'll do that in each molecule. Our group is on the left the way these are drawn because with two carbolic sic acid groups, they're not in the same environment and one will be more acidic than the other. So in this case, we'd expect the one from the backbone to be more acidic because its negative charge is close to the possible positive charge on the amine group. So in that case, we need to remember that the backbone carboxylic acid will give up its proton sooner than the R group carboxylic acid. So let's look at form number one. In this case, we have two carboxylate. Both carboxylic acids have given up a proton and they have negative charges on their oxygen molecules. When we look at the amine group, it is in its neutral form NH two. So this is the fully detonated version of this molecule. And we see that it has a net negative charge. In fact, it is a charge of negative two because there's no positive charge on our amine. So when we're fully deproteinate, when does that happen? Well, that would happen at base in basic conditions. So that would equal high Ph. So we know already that number one primarily exists at a high Ph. So let's look at our answer. Choices. A says that number one primarily exists at low PH. So we can eliminate choice A B says number one primarily exists at high Ph. So we'll leave that choice. C says number one primarily exists at high Ph. And choice D says number one primarily exists at neutral Ph. So we'll cross that out, out of neutral Ph. We definitely wouldn't expect to find that Aming group being deproteinate. So let's cross out choice D now let's look at our next molecule. So our next molecule, number two, we have hydrogens on both carboxylic acid groups. And our amine is positively charged with three hydrogens. It's in the NH three plus form. So this is a fully proton form. It has protons every place that can take it. So that would occur at a low Ph. And in fact, this is a net positive charge on this molecule. So in fact, this would be quite a low Ph given that RP I, the point in which we have a neutral molecule is 3.2. So it's got to be below that. So this is a very low Ph. Indeed. So number two needs to be at a low Ph. So we have choices B and C left. Choice B says number two primarily exists at low Ph. And choice C says number two primarily exists at low Ph. So still have B and C left. Finally, let's move to number three. Well, in molecule number three, our, our group still has a hydrogen on its carboxylic acid. But the backbone groups, the NH three is NH three plus and the carboxylic acid is in the carboxylate form. So we have a positive charge on our NH three and negative charge on our carboxylate. And then our, our group is neutral. So here we have a neutral, I would say net neutral charge. This makes sense because as we said, the backbone carboxylic acid group is more acidic, it loses its proton more easily. Well, we know what Ph is when our molecule is a net neutral charge, that would be a Ph of 3.2 or the range, the area around PH 3.2 because this would be our P I value P I being the value when Ph value at which our molecule has a net neutral charge, this is an acidic R group. So its P I value is low and it's neutral at a low PH. So this is a little tricky because the molecule has a neutral charge. We might be tempted to say this exists at a neutral Ph. But with an acidic R group, the neutral form exists primarily at a low Ph. So when we look at choice B, it says number three primarily exists at a low Ph. So that is correct. Whereas when we look at choice C, it says number three primarily exists at a neutral Ph which is incorrect. So once again, we look at these three different forms of glutamic acid and we have to determine which form primarily exists at low neutral and high ph. Our answer is choice B number one primarily exists at high PH. Number two primarily exists at low PH and number three primarily exists at low ph. See you in the next video.

Which of the following forms of aspartic acid would you expect to predominate at low pH, neutral pH, and high pH?
a.
b.
c.

Verified video answer for a similar problem:

Key Concepts

pH and Amino Acid Ionization

Aspartic Acid Structure

Zwitterionic Form

Which of the following forms of aspartic acid would you expect to predominate at low pH, neutral pH, and high pH?a. b. c.

Verified video answer for a similar problem:

Key Concepts

pH and Amino Acid Ionization

Aspartic Acid Structure

Zwitterionic Form

Which of the following forms of aspartic acid would you expect to predominate at low pH, neutral pH, and high pH?
a.
b.
c.