Titration

in this video, we're going to review titrate Asians. So I'm sure most of you guys have performed hydration in your previous chemistry labs and so recalled it. A tie tray shin is literally just the lab technique that measures the pH changes of acid based solutions. Now recall that titrate shins air typically used to determine the PK, a values of weak acids as well as the concentrations of weak acids. Now, titrate tions can also be used to determine the concentrations of strong acids. But recall from our previous lesson videos that in biological systems most of the assets are weak acids and so moving forward in our course, we're going to focus most of our attention on the Thai tray shins of weak acids, and so recall that the way that titrate Sion's work is that there's an acid based solution of known concentration called the Thai Trahant, and the tie Trahant is gradually added to another solution of unknown concentration called the ANA light solution. Because this is the solution being analyzed now, the Thai trahant is gonna be continuously added to the ANA light solution until a point of neutralization is reached, and this point of neutralization is the exact point where the moles of titrate that are being added is exactly equal to the moles of Anna Light that air present and so the point of neutralization when it has reached its indicated by a color change. So it's pretty easy to detect visually. Now again, a tie Trey Shin is typically used to determine two different things. The first is the concentration of an acid or base in a solution, and the second is the PK of a week. As it now titrate. Asians cannot be used to determine the PK of strong assets. But that's okay by biochemists, because again, most of the, uh, acids in biological systems are weak acids anyways. Now a tight trey shin curve is literally just a plot of the Thai tray shin data, which has the Anna light pH on the Y axis. And it has the amount of Thai trahant being added on the X axis. And so remember that the Thai trahant is continuously added to the solution until a point of neutralization is reached. In this point of neutralization is called the equivalence point, or also known as the endpoint, because once neutralization has been reached. That is the end of an acid. So that's why it's called an end point. Now. This equivalence point for this endpoint is the exact point where the moles of an elite that are present is exactly equal to the moles of Thai trahant that have been added. And so, in our example below, we're gonna look at the titrate shin of a strong acid with a strong base. And again, most of the acids and biological systems are weak acids, not strong acids. And the only reason that we're looking at the Thai Trish in of a strong acid in this example is because when we're trying to refresh our memories off titrate shins, it's easiest to take a look at the Thai Trish in of a strong acid with a strong base and so on. The image on the left Over here. What we have is the set up for a typical Thai tray shin, where we have an early Meyer flash shown below, which has a pink solution in it. And this pink solution is the solution of unknown concentration, which is the Anna light solution. And because this is the titrate in of a strong acid. That means that the analyzed solution in this example is a strong acid. And so notice that in this, uh, analyzed solution, we have this little instrument called a ph electrode, which is going to continuously measure the pH of the analytics solution as we start to add tie Trahant. And so which will notice is up above. We have this Bure AET instrument, which is a volumetric instrument, and it contains the solution of known concentration called the Thai Trahant. And because we're tight trading the strong acid with a strong base, that means that the titrate here is going to be a strong base. And so we're going to continuously add the Thai trahant, uh, slowly into the solution below the an elite solution until the point of neutralization has reached, which is indicated again by a color change. So we would expect the color change and then we would know exactly how much of the Titan we added, and we can go ahead and calculate the concentration of the acid based solution and the peak A if this were a weak acid, But again, uh, this is a strong acid, so we're not able to determine the P A. And so the stop cock here allows us to control the amount of Thai trahant that's being added. And on the right over here, what we have is a tight tray shin curve for the strong acid, with a strong base and on the Y axis. What we have is the pH of the solution. And on the X axis we have the amount of Thai trahant that's being added, and the X Axis units can actually change. Sometimes you'll see that it has the volume of Thai trahant that's being added. But here we have the equivalence of titrate that's being added and mole Arat e. And so a 0.2 Moeller equivalent of titrate that's being added means that 20% of the ANA light solution has been neutralized. A 0.6 Mueller equivalent of Titan that's being added means that 60% of the ANA light solution has been neutralized. And so a one Moeller equivalent of Titra that's being added means that 100% of the ANA light solution has been neutralized. And that is the equivalence point, the point of neutralization and so notice that exactly at one Moeller equivalent. We have this green dotted line here that's indicating the equivalence point and the equivalence point for the tie tray. Shin of a strong acid with a strong base always shows up at a Ph of seven. And so again, the equivalence point is going to be equal to the point where the moles of Anna light. So in this example here, the analytic, remember, is a strong acid, which could be hydrochloric acid here. So when the moles of Anna Light is exactly equal to the moles of Thai trahant and again because we're using a strong base here, we know that the Thai trahant is going to be a strong base, which could be sodium hydroxide. And so, essentially, what you'll see here is, uh, just by looking at this titrate in curve, weaken, tell that we're using We're performing the Thai tray shin of a strong acid with a strong base, and the way that we know is because before we even add any of the Thai trahant, notice that the pH of the analyzed solution is super low below a ph of one, so that lets us know that we're using a strong acid as the Anna light, and then we know that we have. We're using a strong base because noticed that after we reached the equivalence point, the pH goes up really, really high, which means that we're using a strong base to titrate it. And also we know that we're doing a strong acid with a strong base or were performing the Thai tray shin of a strong acid with a strong base, because the equivalence point shows up exactly at a Ph of seven. And so, in our next practice problem will be able to analyze the Thai tray shin curves to predict the type of titrate shin that's being performed. So I'll see you guys in that practice video.

Which of the following titration curves expresses the titration of a weak acid with a strong base?

• A.
• B.
• C.
• D.

So in our last lesson video, we showed an example of the Thai trey shin of a strong acid with a strong base just to refresh your guys. Memories on how tight rations work now because most acids and biological systems are weak acids. In this video, we're going to focus our attention on the Thai tray shin of weak acids. Now, in our last lesson video, we also said that titrate Asians can reveal the PK a values for weak acids. And so the point on a tight tray shin curve that reveals the PKK value of a weak acid is called the inflection point, also known as the midpoint, because that's exactly when half of the acid has been neutralized. And so the point where half of the acid is neutralized is the exact point where the pH of the solution is equal to the P K. A value for ah, weak acid. And so recall from our previous lesson videos that when the pH of the solution is equal to the PK of an acid, that is the exact point where the concentration of conjugate base is equal to the concentration of conjugate acid and so looking down below at our titrate in curve Noticed that this is the tie, Trish in of a weak acid with a strong base, meaning that the weak acid here is going to be our Anna light solution. And of course, the strong base over here is going to be the Thai trahant. And so notice that the equivalence point that we mentioned earlier is being indicated by this blue line and point. And so notice that the equivalence point is showing up at exactly 0.5 or half of the Moller equivalents of titrate that of being added. And so this point, where half of the Mueller equivalence of Titan of being added corresponds with a pH value, and this pH value is going to be the pH that equals the PKK value for a weak acid. And so over here in this chart, you can see that the inflection point, which is also known as the midpoint, is going to be the exact point where the pH of the solution is equal to the P K. A value for the weak acid. And this applies for a week assets on Lee. And so we already know from our previous less video that equivalence points are also known as endpoints because that is essentially the end of oven acid because 100% of the acid has been neutralized. And this is the exact point where the concentration of Anna Light is going thio equal the concentration of Titra or the amount of titrate that has been added. And so over here in our titrate in curve, you can see the equivalence point is being indicated by the green dotted line and point here. And so you can see that it's the exact point where the concentration of Anna Light, which we said was the weak acid, is equal to exactly equal to the concentration of Thai trahant, which we said is a strong base and sodium hydroxide is a strong base, and so you can see that it's a it's showing up the equivalence point, showing up at exactly one Moeller equivalent of Thai trahant that's being added. But which, uh, in our previous lesson video, where we showed, uh, the tight creation of a strong acid with a strong base, we said that the pH shows up at a Ph of seven for the equivalence point. But that is not always the case. The equivalence point does not always equal a Ph of seven. It on Lee equals a Ph of seven when you're performing the Thai tray shin of a strong acid or base with a strong acid or base. And so what you'll see here is that, uh, the pH of the equivalence point depends on the concentration of hydrogen ions, when exactly one Moeller equivalent of Thai trinh is added, and so here for the Thai tradition of a weak acid with a strong base, you can see that when exactly one Moeller equivalent of Titan is added, notice that it corresponds with a pH that is not seven. Instead, it's about a Ph of 8.5. And so that's it's something important to keep in mind about the tight rations of weak assets that the equivalence point do not equal a Ph of seven. And so we'll be able to apply some of the concepts that we've learned here moving forward and our practice problems. So I'll see you guys there

You have an analyte solution of 50 mL of 0.2 M acetic acid (pK_a = 4.8). What volume of 0.05 M NaOH titrant needs to be added to get the final pH = pK_a?

• A. 20 mL
• B. 50 mL
• C. 100 mL
• D. 150 mL

so we already know that some acids are polly product acids, and all that means is that they have multiple acidic hydrogen, and we know that each acidic hydrogen is going to have its own PK, a value. Also, the Thai trey shin curves of Polly Protic acids have multiple inflection points as well as multiple equivalence points. And so there's going to be a set of an inflection point and an equivalence point for each acidic hydrogen. So the number of acidic hydrogen determines the number of inflection points and the number of equivalence points. And so if there are two ascetic hydrogen, there's going to be to inflection points and two equivalence points. If there are for aesthetic hydrogen, then there's gonna be four inflection points and four equivalence points. And so recall from our previous videos that each inflection point on also recalled. Each inflection point is also known as a midpoint. Each inflection point indicates the peak a of an acidic hydrogen and also recall from our previous videos, the Henderson Hostile Back Equation, which is gonna be really helpful for our titrate in practice problems. So keep that in mind, so let's take a look at our example down below, and what we have here is phosphoric acid, which has a chemical formula of H three, p 04 and phosphoric acid is a poly product, weak acid. So it actually has three acidic hydrogen and those three acidic hydrogen czar here, and so notice that the first acidic hydrogen has a PK of 2.2. The second, acidic hydrogen has a PK of 7.2, and the third, acidic hydrogen has a Peca of 12.7. And so over here, what we have is the tie Trish in curve off phosphoric acid with a strong base. And so again, on the Y axis, we have the pH of the Ana light solution. And on the X axis, we have the amount of Thai trahant that's being added and so notice that because phosphoric acid has three acidic hydrogen, there are three inflection points shown by the dotted black lines, and there are also three equivalents points shown by the green dotted lines, and so notice that when the inflection point occurs, that indicates the P K a value of an acidic hydrogen. So the first acidic hydrogen, we said, has a p k a value of 2.2. So notice that the inflection point which occurs right here, uh, it corresponds with the pH value of 2.2. And this is where the PK is. And so when the P H is equal to 2.2, which is the first peek a the concentration of conjugate acid equals the concentration of conjugate base. And so here, because we have, um, h three po four is our conjugate acid R h threepio four conjugate acid is going to equal are conjugate base of H two p o for minus. And so when we get to our first, uh, equivalence point where we add exactly one Moeller equivalent notice that, uh, this is going to be where we completely neutralized the conjugate acid. So at this point here, h three p 04 has been eliminated. So h three p 04 is essentially eliminated or completely neutralized at this equivalence point. And so at the equivalence, point H two p 04 minus is at its maximum concentration. Now, notice that at the second inflection point which is shown up here, there is a ph of 7.2 which indicates the PK A values 7.2. And so when the P H is equal to 7.2, which is equal to this peak a the concentration of conjugate acid is gonna equal the concentration of conjugate base. And here, at this point, what we've done is, uh, the conjugate acid is H two p 04 And so the concentration of conjugate acid H two p 04 minus is gonna equal the concentration of conjugate base, which is H P 04 to minus. And so that would be, at this point here, this midpoint. And so at the second equivalence point over here, what that means is we've added exactly to Mueller equivalents off the Thai trick to neutralize the conjugate acid. So at this point here, what we've done is we've neutralized the conjugate acid, so H two p 04 here is gonna be neutralized. So at this point, h two p 04 is completely gone, and H p 04 to minus is in its highest concentration. So then we continue to add tie Trahant and we get to our third, uh, PK a value our third inflection point and so notice that this inflection point occurs at a ph of about 12.7, which indicates that the P K is 12.7. And so when the P H is equal to 12.7, the concentration of conjugate acid is gonna equal the concentration of conjugate base. And so here are conjugate acid is H P 04 to minus. So we can put that in here H p 04 to minus. And that's gonna equal the concentration of conjugate base, which is this P 04 to three minus p three miles. Oh, and so, as we continue to add more and more tight Trahant, eventually we get to our third equivalents point. And our third equivalents point is, when we add exactly three molar equivalents of Thai trahant and that means that we've completely eliminated HP, uh 04 to minus and that p 043 minuses in its highest concentration. And so, at that point, we have essentially turned all of the acidic hydrogen into hydro knee, um, ions in the solution. And so in our next video, we're gonna be able to get a little bit of practice analyzing some of these tight rations. So I'll see you guys in that video

Use the titration curve below. 

What is the predominate species in the solution of phosphoric acid at pH = 5?

• A. H₃PO₄
• B. H₂PO₄^-
• C. HPO₄^-2
• D. PO₄^-3

Titration confirms an acetic acid solution to be 0.1 M. Calculate the pH. (acetic acid K _a = 1.76 x 10^-5 M).

• A. 2.1
• B. 3.6
• C. 2.9
• D. 8.3