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For more information, please see full course syllabus of Organic Chemistry Lab
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Lecture Comments (2)

1 answer

Last reply by: Professor Starkey
Wed Nov 9, 2016 12:22 PM

Post by Tammie lowe on November 7, 2016

Hi I have a question I did a acid base extraction and I messed up in the beginning of the lab  project , however I added too much HCL, so I had to start over again  I got as far as collecting my basic, acidic and neutral,

I ended putting my acidic solvent in the ice bath, however the class ended, and I had to leave my solution  sitting in lab with small crystals that were presently forming .
Lab is not until next week will my acidic solution be okay sitting in the lab  covered until next week or, should I ask instructor fore new mixture of compounds?

Extraction Lab

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Step 1: Preparing the Separatory Funnel 0:03
  • Step 2: Adding Sample 1:18
  • Step 3: Mixing the Two Layers 2:59
  • Step 4: Draining the Bottom Layers 4:59
  • Step 5: Performing a Second Extraction 5:50
  • Step 6: Drying the Organic Layer 7:21
  • Step 7: Gravity Filtration 9:35
  • Possible Extraction Challenges 12:55

Transcription: Extraction Lab

Hi, welcome back to

Today, we are going to be talking about extractions.0001

More specifically, we are going to be doing liquid-liquid extractions, and do that0005

using a piece of glassware called a separatory funnel or sep funnel for short.0008

It has a stopcock down at the bottom for allowing liquid to flow through or not, if it is parallel to that,0014

if it is perpendicular to the flow here.0021

This can open up, we can take this entire piece out to clean it, if you need to.0026

When you reassemble it, you want to make sure that you can screw this clamp here to make sure it is firm but not too tight.0031

But if it is too loose then the liquid will flow right through, even when this stops.0041

You want to make sure the stopcock is properly tightened before you use it.0046

We do not want to clamp this because we are going to be taking it on and off and using it a lot.0053

A handy way to deal with it is to put a ring stand and something like a triangle here.0058

So that you can just rest it on here and take it off when needed.0063

You want to make sure that you always keep an Erlenmeyer flask underneath it, just in case anything does leak sometimes.0068

When we forget and leave this open and you do not want to pour this and have it pour all over the bench top.0074

We will close it off, when we are ready to add our sample.0080

We can use a funnel so that we do not do any spilling.0084

We take our, let us say we are doing a reaction, if we just finished up a reaction that was done in organic solvent.0090

We add water to this to quench the reaction, neutralize the reaction, and so on.0098

Now we have aqueous and organic layers here.0103

We can pour that mixture into our separatory funnel.0108

Or maybe we have an aqueous layer and we are trying to extract our components into another layer.0111

It depends on what you are going to be doing.0120

But ultimately, we are going to be introducing our compound into our solution into the separatory funnel.0122

We are going to be adding both water, acidic water, basic water,0132

but we are going to have an aqueous phase and then some kind of organic phase.0138

Most organic layers are going to be at the top.0143

They are less dense than water.0146

They are going to be at the top layer.0147

Ether ethyl acetate, something like that, will be at the top.0149

If you use a halogenated solvent like chloroform or methane chloride, that is more dense than water.0153

That is going to be on the lower phase.0158

You want to keep an eye and make sure you know which layer is which.0161

If you ever get confused or if you are ever not sure, you can always take a little of your organic layer,0164

pour a little mixture of our organic layer and watch where it goes or squirt in a little more water and watch where it goes.0169

That for sure, you can be able to confirm which layers is which.0175

What we are going to do is when we have our two layers here, we are going to stopper off the top.0180

What we want to do is we want to mix the two layers.0186

By mixing them, we allow for the solutes that are dissolved in each layer to have a chance to move,0189

migrate to the layer that they prefer to be in.0198

For the most part, organic compounds are going to be moving to the organic layer.0201

Salts or things that are very polar will move to the aqueous layer.0206

The way that we achieve that equilibrium is we have to mix the two layers.0210

Notice that I have my finger on the stopper here, so it does not fall off.0214

I'm going to mix these two layers that are in here.0217

Every once in a while, I'm going to hold this upside down.0221

I’m going to open up the stopcock to allow any built up gases.0223

I'm going to allow them to release the pressure by venting.0231

As you mix, sometimes this warms up a little bit in the organic layer,0235

specially the more volatile one that starts to evaporate.0239

You want to mix gently and then a lot of times you hear a little, as the vapors escape.0243

Sometimes, there is maybe a drop of liquid in the stopcock.0249

Sometimes when you release the vapor, it might spit out a drop of liquid.0253

You want to make sure that every time we are venting, you are doing that away from your face0257

and not aimed at anyone else so that you do not have any hazard of that getting in there.0261

Keeping my finger on this so that it is not going to come off, if any pressure increases as well.0267

Of course I would be wearing my safety goggles.0274

I’m not using any solvents here but I would be wearing my safety goggles and my lab jacket to protect myself.0275

After we mix and we had a chance for those solutes to equilibrate, we are going to put this on here.0283

We need to take the top off because just like when you put your finger on a straw, you can lift up your water out of the glass.0290

We would not be able to drain the separatory funnel, the sep funnel, unless the top is off.0299

We are going to take the top off and now we can open up the stopcock and drain off the aqueous layer.0305

We are going to watch as that line between the two layers comes down.0310

And then right when it gets to the end, we are going to close it off.0315

Now we have our aqueous layer down here and an organic layer up here.0320

Rather than just opening this up and drain the organic layer in here, because this now has water in it,0323

a better practice is to take this off and then pour from the top, pour out your organic layer.0330

That is a way of just getting a little less water into this organic layer.0337

Our typical extraction procedure, let us say, we want to make sure we get all the organic components away from the aqueous layer.0341

We just did one extraction and now we can pour that aqueous layer back in.0351

Again, we can use the funnel.0355

And then, we measure out a fresh portion of our organic layer like our ether maybe.0358

We are going to pour that in here and then we could do a second extraction.0364

What is going to happen is again, those solutes are going to equilibrate.0368

We are going to vent every once in a while.0372

We are going to equilibrate and eventually we are taking out even more organic component from the aqueous layer.0374

And then, make sure it is closed when we put it up here, take the top off.0381

And then, we can drain the aqueous layer once more and we can pour off the organic layer once more.0386

Typically, we do that three times, a total of three times,0395

three fresh portions of ether going in to fully extract out the organic solutes into the organic layer.0397

Now we have this organic layer, the combined organic layers,0408

every time we have an organic extract, we put in the same container.0411

I’m going to hold on to my aqueous layer.0415

I’m not going to get rid of that until I know for sure that I have isolated the compound that I'm looking for.0417

Very easy, when you are doing an extraction to mix up your Erlenmeyer and0423

forget which is what and work with the wrong layer or throughout the wrong layer, or who knows what.0427

It is great to have a marker around so you can label your flasks, as needed.0431

But for sure, do not throw anything out until you know for sure you have your proper cap up.0436

This is my organic layer and my organic layer has water dissolved in it.0442

Because if it is something like ether, there is some water solubility for ether because it is quite polar.0447

We want to get rid of that water.0454

There might even be some water droplets in there, that may have come through in the sep funnel, and so on.0456

We want to get rid of that water.0462

Typically, what we will do is we will use calcium chloride or some other drying agent.0465

This is a solid that we can use a little scooper.0469

We can scoop a small amount in here and we can swirl it around.0475

What is going to happen with the drying agent is, as it absorbs water, it kind of clamps up.0478

We are going to add in a small portion and swirl it around.0484

Very often, what you are going to see is it is going to start to stick to the sides of the flask.0487

Again, notice I’m doing this in an Erlenmeyer, it minimizes evaporation and0491

it is also very easy for me to swirl and it is very easy for me to stand it up, when I need to.0495

An Erlenmeyer is an ideal container for this.0501

Especially with ether, it is so volatile.0505

You got a lot of vapors with that, so let us keep it in a narrow neck Erlenmeyer flask.0507

Let us swirl it around and if it looks like all of the portions of calcium chloride or magnesium sulfite0512

or whatever drying agent I have, I’m going to scoop in another small portion, swirl and watch.0517

Let it sit for a while because the drying is not instantaneous.0526

But we let it sit for a while and then eventually, when I add that last portion and let it sit, that last portion remains freely flowing.0529

You will still see little particulates floating around and not clamping up, that means there is no more water left and your solution is dry.0538

We call it dry, even though it is still a liquid.0547

We say dry because it no longer has water dissolved in it.0550

Sometimes your solution may start out a little cloudy and that is some evidence that it might have water dissolved in it.0554

Not always but sometimes it is cloudy, when you put in a drying agent and swirl it around.0560

You will see it get nice and clear.0564

Eventually, your extraction, your organic layer, after it is dried, should be a clear solution.0568

Now we have our organic layer here, combined organic layers here, and they are dry.0575

But we have to get rid of the calcium chloride.0581

For that, we are going to do a gravity filtration.0584

What you could do is you could actually filter right into a round bottom flask.0587

If you tare this, if I got the weight of my round bottom flask,0591

I know how much it is and that will be useful later in our calculations.0594

I can use a filter, I can use a funnel to just do gravity filtration.0600

I want it to filter as quickly as possible.0604

I’m going to make something called a fluted filter paper.0608

You can actually buy them, pre-fluted if you want, but you can make it just as easy.0611

I’m going to grab a filter paper, I'm going to fold it and fold it again.0615

And then, I'm going to fold it like a fan, zigzag back and forth, and back and forth.0620

When you open it up, you are going to have a fluted filter paper.0627

This has just a lot more surface area so it is going to filter a lot faster.0634

I use my fluted filter paper, fit that in here the best I can.0639

And then, I'm going to filter up my calcium chloride.0647

As usual, I can rinse this with a little fresh ether to rinse off the calcium chloride and0651

make sure that I get all my solution transferred into the tared round bottom flask.0657

We want to make sure we are doing this, so that my flask is never more than half full.0664

Because we are going to put this on the rotovap to remove the solvent.0669

If it is more than half full then it is going to bump in and contaminate the rotovap.0673

Another thing to is you want to make sure we do not use a Buchner funnel.0679

We do not want to vacuum filter this because our solvent is very volatile so that could be a problem.0682

But the simpler thing to think about is, are you collecting the solid?0690

Is the solid what is important or is it the filtrate is what is important.0697

When you are doing a Buchner funnel filtration, that is when you want to collect the crystals that you are saving.0699

You do not care about the filtrate but the gravity filtration is what we are going to use, is when we care about the filtrate.0705

We are just going to discard this into the trash.0710

After it dries, we can put that drying agent into the trash.0713

Now I have my sample, my solution is in the round bottom flask.0717

I can put this on to the rotovap and strip away the solvent.0724

Because I already tared this, I can just get take it to the balance and find out the mass of the flask plus my sample.0728

That is a way I can find out how much sample I have recovered.0736

That is a great way to do an extraction.0739

We can use that to extract compounds, natural products.0742

We can extract all sorts of things but like as I said, an extraction work is a very typical thing we might want to do, when we have finished up a reaction.0748

That is a way to isolate our product and get it away from the,0759

maybe some byproducts and a salt, etc, in there, any water that is in there.0764

Eventually, you can get rid of the solvent that is there and get your product nice and dry and isolated.0768

A couple challenges you might have with your extractions.0775

Sometimes you got emulsions, sometimes the two layers kind of like, when you mix salad dressing,0784

it does not separate immediately into two layers that is because I have added emulsifying agents0789

which encourage the two layers to stay together.0793

Sometimes, components you might have in your reaction mixture might act as emulsifying agents0795

and so they do not immediately separate.0800

What you can do is you can get a, I do not have a glass stir rod with me.0803

But sometimes you can go in with a glass stir rod and kind of separate the two layers.0807

Sometimes there are particulates in there that are causing the layers to not separate.0812

Sometimes you can go back and filter the whole mixture through a Buchner funnel and0818

that will filter out any of those little particulates, that can be a problem.0822

Sometimes just adding that little extra of the organic layer or adding some more water,0826

adding more of each layer can help with breaking up the emulsion.0832

Sometimes you can just swirl it and that helps break it up a little bit.0838

But a lot of times, you know, it is patience.0841

And a lot of times too, if you are noticing certain compounds tend to emulsify, you might want to shake this more gently.0843

You do not want to really to shake it too rapidly because0850

that could cause some of those little bubbles to form and not want to breakup.0852

Sometimes you can add a little brine, it is a little salt water to your aqueous layer0857

that helps draw the water out of that middle layer you get when you have that emulsion layer.0862

Or even some grains of salt can help do that too.0869

Anyway, there is a lot of different options, hopefully, you can avoid emulsions and not have to deal with them.0873

When you do encounter one, make sure you seek out all your options so that you can complete your extraction successfully.0878