Extraction - Online Tutor, Practice Problems & Exam Prep

Extraction is a key laboratory technique used to separate components from a mixture by utilizing their solubility differences in various solvents. This process often involves acid-base reactions, where the pH is selectively altered with strong or weak acids or bases to change the solubility of the compounds in question. For instance, by adding a base to an organic phase containing acetic acid, the acid is deprotonated to form an acetate ion, which is soluble in the aqueous layer due to its polarity. The ion can then be precipitated out as a solid by reintroducing an acid. This method is particularly effective for separating compounds with different acid dissociation constants (pKa), allowing for the isolation of specific acids or bases from a mixture. The technique requires careful pH monitoring using pH strips to ensure complete separation and involves safety measures to release pressure built up during the mixing process. Understanding the principles of acid-base chemistry, including the significance of pKa values, is essential for successful extraction.

Extraction

Hey everyone, so in this video let's take a look at extracting. Now we're going to say under extraction we have the separation of a solid and a liquid, and we're going to say the removal of a component from a mixture is done by selective precipitation in a new solvent. Here already partially colored this in. So here we're doing extraction and here we have it with a separatory funnel. Now we're going to see that this blue portion here is the more dense liquid portion. So that's why it's on the bottom. And let's say that this represents water O Water here would be our aqueous phase for aqueous layer. And then we're going to say up here is our organic layer.

Now let's say that we have two compounds in here in the organic face. Let's say that one of them was ammonia, which is NH3, and let's say that the other one was acetic acid. Now typically with extractions, it's customary to do with acid base reactions. We're going to say acid base extractions is the most common used form and we're going to say the pH of the system is selectively varied by adding strong or weak acids or bases. And we're going to say depending on the pKa of the component, its solubility in aqueous organic solvents will change. So here we're talking about changing one of the two compounds, A&B by adding either an acid or base to the organic phase.

Now here we're going to say formation of an ion equals increased solubility in the aqueous Aqueous solvent layer. Because aqueous water is polar, ions are polar, so they mix together. Non ionic form equals increased solubility in the organic layer, organic layer, it tends to be more non polar. Not having a charge tends to make you nonpolar, so they'll mix together. So what we do here? So for example, let's say we had these two within the organic layer A&B. And let's say I wanted to remove acetic acid from this separatory funnel. What could I do, what I would do here? Since acetic acid is acidic, I can add some base to the separatory funnel. So I'd add some strong base to the separatory funnel. It would seep into the organic layer. And since I'm using a base, the base would remove the proton or H ion from acetic acid and change it into the acetate ion so that the acetate and ion now has a charge. It's polar. So it would travel down out of the organic layer into the aqueous layer.

And now that it's in the aqueous layer, I would drain this aqueous layer into a beaker and there goes the acetic acid on the acetate ion. It's still mixed in there. It's soluble because it's polar I want to keep. I want to make it into a solid. What do I do? Well, you can introduce some acid into here. Introducing an acid would give back an H plus ion to the acetate ion and change it into acetic acid. Since acetic acid is neutral, it would precipitate, and since it's precipitating, it's a solid. I can just drain the aqueous portion and have left some of this precipitate at the bottom, and in that way I've separated my 2 compounds A&B from each other by using extraction with the use of a separatory funnel.

Now, how can I make sure that all of the acetic acid is no longer in the organic layer? Well, you're adding base. If there's any assets still remaining, the pH of the organic layer would still be a little acidic, so you just use pH strips. You dip it in there to make sure that the organic layer is completely basic. That means the base has completely neutralized any potential acetic acid. Still remaining Another thing about this, since this is an acid base reaction, you're mixing acids and bases together. They would build up pressure because in order for things to mix, you would invert the separatory funnel to make sure that there's thorough mixing between the base and the acetic acid. This will cause a buildup of pressure as you're inverting it. Mixing it thoroughly, you would make sure you have the end portion of the separatory funnel pointed up. Twist This opening here allow some gas to exit, so it's pretty involved work when you're trying to use a separatory funnel by using extraction of these two tyes of compounds.

In the next video, we'll take a closer look of what would happen if we had even more compounds mixed within a solution. How could we use this acid base extraction in order to separate each one of these compounds from one another?

Acid-Base Extraction

In this video, we're going to take a look at an acid base extraction. Now we're going to say whenever you do an acid base extraction, typically it is better to add a weak base before a strong base. That's because the most acidic component will react with that weaker base. If we were to use a strong base from the very beginning, all the acidic compounds would all react with it, and in that way we wouldn't be able to thoroughly separate them from one another.

So we're going to say this allows us to only isolate the strongest acid and that won't become negatively charged and therefore become aqueous or become soluble in the aqueous layer. Now here I'm giving us different compounds and with them their PKAs. Remember the lower your PKA is, then the stronger the acid. This is going to require you guys to know some basics about acids and bases. So make sure you've looked at my videos dealing with acid base identification.

Now if we take a look at these, we have here, this first compound is called propane. Its PKA is 60, so it's pretty high. Next we have methylamine which is 10.64. Next, we have what's called Phenol. We write them all down. You don't need to know how to name them, I'm just giving you the names for them. And then we have acetic acid finally. So the lower your PKA, the more acidic you are. We can see that acetic acid has the lowest PKA present, so it's going to be the most soluble.

Now, here, at the moment, they're all found within the organic layer of your separatory funnel. All right. Your separatory funnel, not the best drawer, but hopefully you guys understand what I'm writing. So what we have here is our organic layer which has all four components in it. And then below that is our aqueous layer, which is more dense, heavier. That's why it's on the bottom, right? So in the organic layer, they're all neutral, so they're all going to be found in the nonpolar organic layer.

What you're trying to do is react the solution with an acid or a base at each step. This will cause some of the compounds to gain charges. Once they gain a charge, they're going to slip down into the aqueous layer because the aqueous layer is polar, and when you gain a charge, you become polar. And once they're in the aqueous layer, we can drain out that aqueous layer and separate that component from the rest of them. Then all we do is we re-add more water which will naturally seep down to the bottom and do the process over again.

So here what we do first is we react these four guys in the organic layer with two five molar sodium bicarbonate which is just baking soda which is weakly basic. So this would react with the strongest acid present and the strongest acid present is the acetic acid. It would react with the base, so it would donate an H plus to the base and become my acetate ion. So here goes your acetate ion. It's now in the aqueous layer because it's gained a charge. And then the remaining guys here, they're not as acidic, so they won't react with the sodium bicarbonate. So they're still in the organic layer.

Now here in the aqueous layer that's in, we want to make it a solid within that aqueous layer. At the moment, it can't be a solid because it's charged and making it polar, so it'll dissolve in a polar solvent. What we have to do here is to take away its negative charge, and we do that by giving back its H plus. So we use some acidified water. So this is acidified water that acidified water which is donated H to this, making it neutral again. And now it would exist as a solid in the aqueous layer.

Now we got to continue. So we've gotten rid of the most acidic component out of the four. Now we have these three remaining. So now we're going to use a stronger base, so we use sodium hydroxide. That stronger base will react with the next most acidic compound, which is the phenol. It takes away its H plus, so becomes C₆H₅O^-. We don't take away one of these here because those are connected to carbon, and a carbon hydrogen bond is not very acidic, so they'll stay there. We're always taking hydrogens from either end. This H technically is not connected to the carbon. The formula is deceiving that hydrogen is actually connected to the oxygen in phenol.

So here we get our phenolate ion. It has a charge, so now it is in the aqueous layer. And because it's in the aqueous layer, it's gonna be polar, but we need to make it neutral again. So again, we use acidified water, which is going to donate an H plus to the phenolate anion and give us back phenol. It's neutral again, so it becomes a solid within the aqueous layer.

So what do we have left? We have left are propane and are methylamine. So if you recall my videos on identifying acids and bases, remember that compounds made-up of only carbons and hydrogens are nonpolar, therefore they're not acidic or basic. So this is always going to be found within the organic layer. So there's nothing we can do about that. And then methylamine, in the name we hear the term amine. Remember, if you're a neutral amine, meaning you have no positive or negative charge, you are a weak base. Because you are a base, you will react not with a base but with an acid.

So we switched up a little bit here. Instead of using a base, now we're using an acid that HCL will donate in H Plus to the methylamine and here becomes Chapter 3 and H₃⁺. So it becomes methyl ammonium ion and because it has a charge, it's going to be in the aqueous layer. OK. But here now we technically aren't going to use acidified water. What we're going to do instead of actually, we're going to use OH^-, we're going to use some base. The base will rip off hydrogen here. It's going to accept an H plus so that this can become neutral again. And now it's going to be a solid in the aqueous layer.

So this is how we perform an acid base extraction. It allows us to separate different solids from solvents by introducing a new solvent. Again, it's hard to do this if you don't understand the principles of identifying acids and bases in which we talked about. So make sure you take a look at the chapter when we talk about acid and bases, how do we identify them as being an acid or a base, weak or strong? What is a high KA mean? What is a low PKA Mean? The higher your ka, the stronger the acid, the lower your PKA, the stronger the acid. This all these things built up in terms of being able to do this laboratory technique in which we use different PHS and different affinities towards acids and bases to help separate solids from a liquid.