Extraction involves the separation of a solid from a solution mixture by selective precipitation.
Mixture Separation
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Extraction
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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 I 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 say 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. So water here would be our aqueous phase or aqueous layer. And then we're going to say up here is our organic layer. Now let's say that we have 2 compounds in here in the organic phase, 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 gonna 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 gonna 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 2 compounds A and B by adding either a acid or a 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 liability in the organic layer. Organic layer tends to be more non polar, not having a charge tends to make you non polar, so they'll mix together. So what we do here, so for example let's say we had these 2 within the organic layer A and B, and let's say I wanted to remove acetic acid from this separatory funnel. What could I do? What 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 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 Well, you can introduce some acid into here. Introducing an acid would give back an H+ ion to the acetate ion and change it into acetic acid. Since acetic acid is neutral it will 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 and 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 acid 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 to 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 types 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?
A separatory funnel is the commonly used instrument for extraction. In it, two liquid layers are used for the selective precipitation of a solid from the liquid phase based on difference in density and solubility.
The most common form of an extraction is an acid-base extraction, which uses the different acidities of compounds to selectively precipitate one compound over another.
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Acid-Base Extraction
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In this video, we're gonna take a look at an acid base extraction. Now we're gonna 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're to use a strong base from 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 gonna say this allows us allows you 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, they're pKas. Remember, the lower your pKa is, then the stronger the acid. This is gonna 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 p k is 60, so it's pretty high. Next, we have methylamine, which is 10.64. Next, we have what's called phenyl. 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 gonna be the most soluble. Now here, at the moment, they're all found within the organic layer of your separatory funnel. 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 4 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 gonna 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 4 guys in the in the organic layer with 0.25 molar sodium bicarbonate, which is just baking soda, which is weekly 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 wanna make it a solid 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+. So we use some acidified water. So this is acidified water. That acidified water, which is donating h+ to this, making it neutral again. And now it would exist as a solid in the aqueous layer. Now we gotta continue. So we've gotten rid of the most acidic component out of the 4. Now we have these 3 remaining. So now we're gonna 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+, so it becomes c 6 h5 o negative. 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 those stay there. We're always taking hydrogens from either end. This h technically is not to the carbon. The formula is deceiving. That hydrogen is actually connected to the oxygen in phenyl. So here we get our phenylate 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 gonna donate an h plus to the phenylate anion and give us back phenyl. It's neutral again, so it becomes a solid within the aqueous layer. So what do we have left? We have left our propane and our 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 gonna 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 it up a little bit here. Instead of using a base now we are using an acid. That HCl will donate NH+ to the methylamine. And here it becomes CH3 NH3 positive. So it becomes Methylammonium ion. And because it has a charge, it's gonna be in the aqueous layer. K? But here now, we technically aren't gonna use acidified water. What we're gonna do instead, actually, we're gonna use Oh minus. We're gonna use some base. The base will rip off a hydrogen here. It's gonna accept an H+ so that this can become neutral again. And now it's gonna 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 does a high Ka mean? What does a low pKa mean? The higher your k a, the stronger the acid. The lower your p k a, the stronger the acid. This all these things build 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.