Isoelectric and Isoionic pH - Video Tutorials & Practice Problems
On a tight schedule?
Get a 10 bullets summary of the topic
Isoelectric and Isoionic Points
1
concept
Isoelectric and Isoionic Points
Video duration:
3m
Play a video:
Video transcript
we're gonna say here that are Isil Elektrik or Isil. Ionic points represent the ph where a polyp protic acid doesn't migrate to an electrical field or electric field because it's neutral. Traditionally, when we talk about electronic and ionic points, we refer to amino acids. Now a lot of amino acids have to P. K. Values because of their acidic car box a group and their amino group that can be propagated to act as an acid as well. Now we're going to say here that at the ice electric point we have an amino acid that has a negatively charged car box A group and a positively charged ammonium group. Now we're going to say here that overall the amino acid is neutral because the negative and the positive end cancel each other out. We're gonna say at the ice electric point, your amino acid exists as a sweeter and ion. So we have our car boxes group here are ammonium ion group here here this carbon that is next to the car boxes group is referred to as our alpha carbon. And we'll just write the alpha symbol actually. And the alpha carbon has connected to an alpha hydrogen. There are 20 different amino groups or amino acid groups because there are 20 different r groups when it comes to amino acids. If we dump this Zorro and ions in a solution that is more acidic. What's going to happen is we're going to pro tin eight. This car box cell group and by protein mating it now it doesn't have that negative charge. It has this newly acquired H plus group and all that remains. Is this positive charge. So we're gonna say below our ice electric point where the solution is more civic, we exist as a cat ion. If we go the opposite way and we throw the switch and ion into a more basic solution, What's going to happen is we're going to deep protein eight or remove an H Plus from this ammonium group here. As a result it becomes N. H two which is neutral overall. The charge of our amino acid to be negative. So we'd say that in a more basic solution which is above the ice electric point of my amino acid, my amino acid would exist as an an eye on a negative ion. Now as a cat ion or an ion, they would be affected by an electric field. The cat eye on being positive would be attracted to the negative plate of an electric field. And the an ion which is negative would be attracted to the positive plate of an electric field because remember opposite charges attract one another as is water and ion were at the electric at the ice electric point for an amino acid, it's neutral overall and it's not attracted or repelled by an electric field. Now that we've gotten the basic idea behind ice electric. And so, ionic points, click on the next video to see the calculations that are involved with both of these two points and how they were late to the sweeter ion, or intermediate forms of compounds.
2
concept
Isoelectric and Isoionic Points
Video duration:
6m
Play a video:
Video transcript
So here we say that at the so ionic point the polyp protic acid exists as an intermediate. And so we can utilize past equations to determine the concentration of H Plus. Now remember for di product system or die protic acid, we have three forms. We have the acidic form, we have the intermediate form and we have the basic form. Here we only have one intermediate form and the concentration of H plus for that intermediate form equals the square root of K. One times K two times the formal concentration of my dia protic acid plus K. One times K. W. Which remember is 1.0 times 10 to the negative. 14 at 25 degrees Celsius divided by K one plus the formal concentration again for a polyp protic acid. Traditionally try product acids are the most common polyp product acids discussed. We have the acidic form. We have the first intermediate form. We have the second intermediate form. And then we have our basic form. Here we have two intermediate forms, which is why we have two different equations. So remember here we be dealing with H plus for the first intermediate form and here would be dealing with H plus for the second intermediate form. Remember that P K P H here equals P K one, P H E R equals P K A two. And then here P H equals P K A three. Depending on where your ph lands. In terms of being in here or being in here can help us determine um which equation really is useful in terms of determining ph or H Plus in this case. Now the electric point is the ph where the acid form is equal to the conjugate base form and therefore the average charge is equal to zero. Now again, if we're dealing with a dye product, acid dye product assets have two K. A values. K. One where we remove the first acidic hydrogen to give us our intermediate form and then K two, which gives us our basic form. Also remember here that K two would be connected to KB one and then K one would be connected to KB two. Here, we really don't need to worry about the KB values. Just realize for dia protic acid ph for the ice electric point which sometimes is written as P I equals half the P. K one plus the P K two with polly protic acid. We run into the issue again of are we talking about the first intermediate form or the second intermediate form? So we have two different equations. Here we have P. H equals half P. K one plus P K two. When we're dealing with the first intermediate form and then here we have P. H equals half P. K two plus P K 31 dealing with the second intermediate form. Now, traditionally when we talk about ice electric points, we relate them to the amino acids. Now for this first ice electric point where we're dealing with the two lower P K. A values. This is traditionally used for the acidic amino acids. So the acidic amino acids have three P. K. S. Here we use the the two lower P K. Values that they have out of the three. And examples of our acidic amino acids would be a Spartak acid Which has a three letter code of ASP. And the one letter code of deep and glue tannic acid. Glue tannic acid has a three letter code code of G. L. U. And the one letter code of E. So if we're dealing with determining the ice electric point of Spartak acid or glue tannic acid, they both have three PK values. But we use the two lower P. K values to find the ice electric point. Now here we're dealing with the two larger P. K. Values. P. K. Two and P. K. Three. This is traditionally used for the basic amino acids like the acidic amino acids. They also have three P. K. S. But we're focusing on the two larger P. K values. To find the ice electric points. Your basic amino acids would be Argentine Sergeant nine, which has a three letter abbreviation of A R. G. One letter abbreviation of our. We also have histamine which has a three letter abbreviation of hiss And one letter abbreviation of H. And then lie scene would be the last basic amino acid here. It B. L. Y. S and K. So remember when we're talking about ice electric points, we traditionally refer them to amino acids. When we're talking about polyp protic acid, we're talking about amino acids with three P. K values, die product acids, those are just normal amino acids that are not acidic or basic. They only have two P. K values that we can use. So there's only one equation for them. And then also remember that when we're talking about the ice electric point, we're really referring to the intermediate form of your die protic acid or your polyp protic acid. We're calling the equations for the intermediate forms for di product system. And a polyp product system is essential on our path of determining what our ph will be. So keep in mind these different definitions and how they relate to these different formulas.
3
example
Isoelectric and Isoionic Points Calculations 1
Video duration:
4m
Play a video:
Video transcript
So here we're told to calculate the Isil Elektrik and isil ionic ph of 0.25 moller glutamine. Here. Glutamine has to P K. S. P. K. One equals 2.19. And P K two equals 9.0. This is neither an acidic or basic amino acid. That's why the third PK is not given. Now here to determine our Isil Elektrik point, we can say here that ph is equal to half my P. K. One plus my P. K. Two. So that's half of 2.19 plus 9.00. Which gives me a final ph of 5.60. For the Isil ionic ph any time we have to find the Isil ionic ph we assume that we're dealing with the Saturn ion of the amino acid. So it's intermediate form, it only has two P. K. S. So it is a dye product system. So in that case H plus one equal square root of K. One times K. A two times the formal concentration of my amino acid plus K. One times K. W. Divided by K. one plus the formal concentration, we're gonna say here that my K. One equals 10 to the negative P. K. One and my K two equals 10 to the negative P. K. Two. Now that we have those values, we can plug them into the formula. So it equals square root of 10 to the negative 2.19 times 10 to the negative 9.00 formal concentration is .025 plus 10 to the negative 2.19 times 1.0 times 10 to the negative 14, Divided by 10 to the negative 2.19 plus. The formal concentration of .025 molar. Here. When we work out the problems on top and on the bottom, we're gonna get 1.61478 times 10 to the negative 13 on top, divided by 130.31457 on the bottom. When we take the square root of that ratio, we're gonna get as our final concentration for H plus as 2.265 or +66 times 10 to the negative six Mohler. So that represents the concentration of H plus, taking the negative log of it. Well, give me my ph So here my p. h. equals approximately 5.64. Realize here that when it comes to determining the Isil Elektrik and isotonic ph of a Dia product or polyp product system, the values will be very close to one another here. The ionic ph because it involves the use of more values and the actual concentration will be closer to the actual ph of my dia product or polyp product system. The ice electric point. Although close um usually is not as accurate but don't worry, both of the values should be very close to one another. Any time you do both of these processes. Now that we've seen this attempted to example two draw the structures in charge of a Spartak acid at a ph of 9.82, so Spartak acid represents an acidic amino acid. Therefore, it's gonna possess three P. K. Values based on those p. K. Values determine which form would predominate at the given ph. Once you've done that, come back and see if your answer matches up with mine.
4
example
Isoelectric and Isoionic Points Calculations 1
Video duration:
3m
Play a video:
Video transcript
So here it says draw the structures in charge of a Spartak acid at ph equal 9.82. So Spartak acid represents an acidic amino acid, so possesses three P. K values. It's PK. one value equals right, I'm up here, P K one equals 1.88. And that is for its alpha carbon silic acid group. So that's the car box a group that's connected to the alpha carbon. P. K two equals 9.60. And that is for the ammonium group connected to the alpha carbon. And then finally P. K three equals 3.65. That is for our our group here, we're gonna say that the first way we can draw this structure is we have a car basilica acid, which is my our group here is my ammonium group that's connected to my alpha carbon and here's the other carbon silicate acid group. Here we're talking about PK. A. one. Well, P. H equals P K. One. Once we pass this line here, it becomes basic enough for us to remove the most acidic hydrogen, which is the hydrogen with the lowest PK value. So that means that we're losing this hydrogen here. So here we look like this. Now Here, when we cross when we get to this line, P. H. equals PKA two. Once we pass this line we're gonna remove the next acidic hydrogen most acidic hydrogen, which would be this hydrogen. So now we have this form of my amino acid. And then finally, what we're dealing with P K. Three, we have P. H Equals P. K. A. Three. And beyond this point were basic enough to remove the last acidic hydrogen, which is one of these hydrogen is here for the ammonium group. So now we have this neutral form NH two. So here the value will be 1.88. Here would be 3.65 and here is 9.60. The ph is 9.82. So we've gone beyond this line here. So the predominant form of the amino acid would be this form where all the acidic hydrogen have been removed. So this is the view of the amino acid once the PH hits 9.82. So remember this is dealing with amino acids but it's piggybacking off of concepts we've seen before where we're relating ph two P. K. A. If the ph is greater than the peak A. We have enough of a basic enough environment to remove an acidic hydrogen. Now that we've seen this example, attempted to practice question one were asked to figure out what our P. I. Value is for the given amino acid. Once you've attempted this, come back and see if your answer matches up with mine
5
Problem
Problem
Calculate the pI value for histidine. pKa1 (carboxyl group) = 1.60, pKa2 (ammonium group) = 9.28, pKa3 (R-group) = 5.97.
A
7.63
B
1.65
C
5.44
D
3.74
E
5.62
6
Problem
Problem
Calculate the pI value for gluatamic acid. pKa1 (carboxyl group) = 2.16, pKa2 (ammonium group) = 9.96, pKa3 (R-group) = 4.30.