This work was created by Dr Jamie Love and licensed under a Creative Commons Attribution-ShareAlike 4.0 International License Creative Commons Licence.

PRINCIPLES OF ALCHEMY

WATER

Can you change any chemical into a gas, liquid or solid by changing its temperature?

That depends on the specific molecules you are talking about. Remember, many kinds of molecules cannot stand up to high temperatures. Their internal bonds (intramolecular bonds) will be broken by increasing the temperature, so those molecules will break up into their parts before becoming a gas (or liquid). It really depends on the specifics.

So you can't turn just any solid into its liquid or gas by increasing its temperature. It depends on the strength of the bonds that make up the molecule.

Right!

I bet you can always turn any liquid or gas into a solid. Right?

Aye, you can if you reduce the temperature far enough. Intramolecular bonds won't be harmed by making the molecules colder. Indeed, the bonds may be strengthened.

Yeah, and that's why it will change to a more rigid state of matter at the colder temperatures. Right?

Right again.

Hmm. You know some of these solid states of matter are pretty complex. Like glasses.

Yes, and I'm glad you remembered to call it a solid. Some people (even chemistry teachers) have a crazy idea that glass is a liquid!

What!? But that doesn't make sense. Glass retains its shape. It doesn't reshape itself to fit inside a container. Unless of course, its molten glass, but that's different. At high enough temperatures you have liquid silicon dioxide, but at normal temperatures it's a solid. Right?

Again, you are right, more right than some folks who are confused by glasses. I'm glad you fell back on the definition of a solid as a state of matter that doesn't change its shape. That's the correct physical description of a solid. And remember, the reason a solid is a solid is because it has lots of stable intermolecular bonds (bonds between molecules).

Hey, what about toffee? It's a solid but amorphic form of sugar. It's a glass of sugar (so to speak). It's solid but it isn't very solid. I can break it with my hand.

That's right. However, it's still a solid - a weak solid. The intramolecular forces holding the sugar together (at comfortable temperatures) are not strong. On the other hand, the bonds that hold the carbon atoms together in a diamond are very strong. They're covalent! You cannot break a diamond with your hand.

I see. But I can break glass! Window glass. It breaks easily!

Yes, but it is still a solid.

Oh, yeah! And so is toffee. Gee, there are lots of different kinds of solids.

Aye. Some solids are hard, some are soft and some are brittle.
Diamonds are a hard solid. Sugar crystals are solid too but not as hard as diamonds.
Toffee is a soft solid .You can easily break it with your hands and it falls apart simply. Toffee doesn't have the regular structure of a sugar crystal, but it's still a solid, an amorphous solid. Amorphous solids are also called a "glass". Window glass is another amorphous solid but it's harder than toffee and it's a brittle solid. It will shatter when you hit it. That's a slightly different behavior from toffee. They are both glasses but the difference has to do with the details of their intermolecular bonds.

Let's not go into it any further. I think you've convinced me that solids are pretty complex and we've talked about all the possible types of solids.

Well, no we have not covered gels.

Gels! What are gels?

Gels are another unusual solid and I think a "Do This!" will show you what I mean.

Oh, good. Let's do something.

Get a clean (unused!) disposable diaper.

A what!?

A disposable diaper is the kind you throw away after the baby has used it. Almost any household with a baby will have them.

OK, I found this one in your box of junk. Now what?

First lay out some papers to protect the table top and to help you collect the material from inside the diaper. Now use some scissors to cut the diaper into bits. Do this over the paper and gently shake out the diaper bits.

Look. A white powder is falling out of them.

Aye. Try not to breathe it in. (It will probably make you sneeze.) Now collect some of that powder. You do not need much. A teaspoon full is more than enough.

OK. What next?

Pour the powder into a clear glass or cup. Now pour some water in. Fill the glass about half full. Swirl it around a bit and ...

Hey! The water stopped swirling! It's turned into a solid! Magic!

It seems like magic but it's easily explained Alchemy. In fact, you have made a wee mistake. The water hasn't become a solid.

Yes, it has! Look, I can even turn the glass upside down and it stays inside the glass. It's a solid. It feels gooey but it's a solid.

You are right that the material in the glass is a solid, but you are wrong to think that it is solid water. It is NOT solid water, it is a gel of water.

Huh?!

A gel is a special kind of soft solid made mostly of liquid. It is solid because of the other chemical(s) in it, not because of the liquid.

What is that other chemical? What was in that disposable diaper? What's that powder?

Sodium polyacrylate. It is an ionic-covalent compound. When you add it to water (or add water to it) the ionic portions dissolve into the sodium cation and the polyacrylate anion.

What's polyacrylate?

Polyacrylate is a long, covalent, anionic molecule. To properly understand it you need to learn some Organic Alchemy, but we don't need to go into that in order to understand the idea of a gel. Polyacrylate is a long fiber of carbons and other atoms. When dissolved in water those fibers attract water molecules to it. Water molecules become attached to the fibers, not permanently but as a loose association.

Hmm. I guess it has this gooey feel because the water is loosely associated with it. Kind of like bread dough.

Yes! Bread dough is a gel too, but not a very good one. Flour absorbs only a small amount of water. Baking the dough removes most of the water and forms the bread.
Polyacrylate holds much more water than flour can hold. Polyacrylate can absorb up to 80 times its weight of water! We say that polyacrylate is very "absorbent", meaning ...

It sucks up water!

Right. In the 20th century a chemist thought of using polyacrylate to absorb the moisture from babies. It's also used to clean up nasty chemical spills.

You mean, like the nasty chemicals that babies spill?

Well, yes. But I was thinking about other more "industrial" spills. You see, because the water is attached to the polyacrylate fibers, so too are any chemicals that happen to be dissolved in the water.

So it's a chemical sponge.

Yes, exactly!

And it's a solid.

Aye. Gels are a soft solid (most of the time) because they are mostly made of water. However, it is not solid water, it is a gel made of water and another chemical. Together the two (water and polyacrylate) make a gel.

I see. Water is still water and it's mingled among all the fibers of polyacrylate.

Yes. The gel is swollen full of water. Gels are an interesting kind of solid. You should know that they are a mixture of a liquid and a solid. The liquid, water in our example, is still a liquid and its association with the fibers is not too tight so each water molecule actually moves around in the gel.

I see. Because the water molecules are still free to move around they are still a liquid.

Very good. The polyacrylate is a net that contains the water.

So the polyacrylate is acting like a container for the water. It's an inside-out container!

Hmm. I hadn't thought of it that way, but you are right. Each water molecule will move around inside the gel and does so pretty freely. Yes, the polyacrylate is containing the water.

You know, I could turn this into a neat little magic trick.

Oh? how?

I'll collect more of this powder ...

Sodium polyacrylate.

Yeah, and I'll put it into the bottom of a cup that is NOT clear. Then I'll show the folks that I can pour water into it, swirl it and I'll turn the cup upside down to make them think the water has disappeared.

That would make a very nice magic illusion.

It will be a great magic illusion!
Hey, what would happen if someone swallowed this stuff?

What do you think would happen?

Well, the polyacrylate would absorb any water it could get. I guess it would then turn to a gel and gum up that person's insides. Yech!

That's right and that could kill them! This is a good time to remind you about safety.

Oh, no!!

Now, now Arthur. Safety is important. The magic illusion you described is a good idea and a safe use of your Alchemy knowledge, but you should be aware that some "gags" are very dangerous. Some people might think it funny or a good revenge gag to give someone polyacrylate, but it can kill. Only an evil Alchemist or King would even think of doing such an awful thing!

OK, I'll never give it to anyone to eat. Hey, what would happen if I put this polyacrylate into my fish bowl?

What do you think would happen?

Ah, if I put enough in the tank the water would turn to a gel and my fish would be trapped inside it.

Yes, and that would kill the fish. The gel would gum up his gills just like it would a gum up person's insides. Your fish would experience a pitiful death.

OK, I won't do that either. I guess I'll stick with my magic trick.

That's a good idea. It's also a good idea to clearly label any chemicals you collect. If you collect a pile of sodium polyacrylate be sure you label the bottle clearly. It stores well but you wouldn't want someone to mistake it for candy or food.

OK, I'll write "sodium polyacrylate" on the label. And "poison" too!

Good idea. That's the way a proper Alchemist behaves.

Hey, if this stuff is so dangerous, how come you can have it in babies' diapers? Huh?

Because the sodium polyacrylate is packed inside the lining of the diapers. Even babies can't eat diapers! Any other questions?

Yeah. What's a wizard doing with disposable diapers?!

I'm glad you asked. The last time I visited the 20th century I wanted to get some sodium polyacrylate for my plants here at home. Unfortunately I didn't have time to stop at the gardening center so I just popped into the local store and picked up this box of disposable diapers. I collect the sodium polyacrylate for my hanging basket plants.

OK, why do your plants need disposable diapers? I mean sodium polyacrylate. I'm confused.

Polyacrylate has many uses. I (and other gardeners in the 20th century) mix sodium polyacrylate into the soil of potted and hanging-basket plants. That way I can give them plenty of water all at once. The polyacrylate absorbs most of the water. As the days go by the plant's roots are able to suck the water out of the polyacrylate and stay "watered" without me having to water them each day.

I see. The polyacrylate lets you be lazy and forgetful.

I like to think it allows me to have plants around the house even when I'm away and can't water them.

I see. I guess these gels have lots of uses.

Yes, they do. Gels are used in some industrial processes in the 20th century. And most of life is a gel!

What!?

Life is made of cells and most of cells are a kind of gel. Instead of using polyacrylate they use a wide variety of proteins and other polymers. Cells are microscopic and they use complex BioAlchemy of their own to change liquids to gels and back again. Some cells (amoebas, white blood cells, etc.) use these gel and liquid changes to move around. These strange kinds of solids are very useful and interesting.

I see. Gels are liquids trapped inside a net of a solid so gels are solid. However, gels are mostly made of liquid so the best gels absorb lots of liquid, but they are still solid because they hold their shape when taken out of the container.

Right.

And a solid can also be a crystal with regular repeating units, or amorphic (a glass) like toffee and windows.

Right again. Try to remember the various kinds of solids (crystals, glasses and gels) and their properties.

How about a "Do This!" to learn hydrophobic and hydrophilic interactions?

OK, do this!
Pour some water into a clear glass, so there is an inch or so in it. Then add a similar amount of cooking oil (vegetable oil). Cooking oil is made of a string of carbons with hydrogens attached.
You will see that the two liquids do not mix. The oil is less dense than water so it floats on top of the water. You can see the difference between the two liquids if you look carefully. The place where the two different liquids meet is called the interface.

Yeah, and the oil has a little color to it, so it is easy to see the difference. Are they separated because of the hydrophobic and hydrophilic interactions? Or is it because water is denser than oil?

Both. The difference in density makes the separation easier. However, it is the hydrophobic interactions that keep all the oil molecules together and the hydrophilic interactions of the water molecules that keeps all the water molecules together.

I see. All the water molecules form temporary hydrogen bonds between themselves and that keeps them together.
Do the oil molecules also form temporary bonds?

Of course, yes. If the oil molecules didn't form any bonds between each other the oil would be a gas.

Oh, yeah. I forgot. So, how do these oil molecules bond to each other? Do they use hydrogen bonds too?

No, oil doesn't make hydrogen bonds. It has to depend upon van der Waals interactions to form its temporary bonds. Fortunately, oil is a long organic molecule. So it can make enough temporary bonds to make a liquid at room temperature.

So it's like paraffin.

Similar to paraffin, but not quit so large a molecule. If oil were as large as paraffin, these oils would be a solid at room temperature, like paraffin.

So vegetable oil is a large molecule, but not as large as paraffin.

Yes.

Wait a minute. If oil molecules are that large, they should be larger than water molecules, right?

Yes, they are. Oil molecules are about ten times larger than water molecules.

Then why isn't the oil on the bottom of the glass? It should be heavier than water, if the molecules are larger.

Not necessarily, but I can understand why you might think that way. Remember, it is the denser molecules, not the heavier ones, that sink. The oil molecules are larger, but they are not as tightly packed as water molecules. So oil floats on water. Don't be mislead by the density differences. Density has to do with both the mass and the volume of the molecules. That's not what I want to teach you today.
What you should note is that the two liquids will not mix (easily) because the water is hydrophilic and the oil hydrophobic.

Water and oil don't mix, because hydrophilic and hydrophobic don't mix.

Yes, very good!
This separation of two liquids by their hydrophobic and hydrophilic interactions is an important technique in Alchemy. We can use it to isolate, purify and help to identify different chemicals.

For example?

Gently add some food coloring, just a few drops, onto the top of the oil. You will see that the color just floats about in the oil. Eventually it sinks to the interface. What does that make you think about food coloring? Is it hydrophobic, like the oil?

No. If the food coloring were hydrophobic, it would dissolve in oil, right? "Like dissolves in like." Isn't that some Alchemy rule?

Yes, it is. You are absolutely right. Food coloring is not hydrophobic. Now, use a spoon or something to push the drop of food coloring through the interface, into the water layer below. You'll see the drop(s) sudden spill into the water layer.

That's very different behavior from the way the food coloring behaved in the oil layer. I bet the food coloring is hydrophilic. It loves water, so it dissolves in it.

You're a smart lad, Arthur. That is absolutely correct. Oil is hydrophobic and thus resists being colored by the food color. That is, the food coloring will not dissolve in the oil. Because the food coloring is hydrophilic (water loving) it dissolves in water, not the hydrophobic (water fearing) oil. "Like dissolves in like."

Is this trick useful to Alchemists?

Yes! Alchemists use this "trick" to move molecules from one liquid to another. It is common for Alchemists to create new hydrophilic molecules from hydrophobic ones. (Exactly how, is an advanced topic.) These hydrophilic molecules will be made in the oil, but the oil is hydrophobic. So by adding a bit of water, Alchemists can make the newly created hydrophilic molecules run into the water. That leaves the oil, and any hydrophobic molecules that have not changed to hydrophilic ones, trapped in the oil layer. Or an Alchemist could do the reactions and separation the other way around, swapping hydrophilic and hydrophobic.

So Alchemists use these differences in hydrophilic or hydrophobic character to separate molecules. Including molecules they've created in the liquids.

Indeed. We call it solvent separation, and it is a very important part of applied Alchemy. This experiment nicely illustrates how that is done. Try adding other things and see how they dissolve (or not) in each type of liquid. Add some salt and watch where it dissolves. Try sugar. Try some ink from a pen. Try lots of things! (NOT fish or other water creatures. The oil may kill them!)

You know, I find this evaporation thing to be strange. It isn't boiling, right?

Right. Evaporation is NOT boiling. During evaporation the liquid's molecules escape into the air as a vapor, not as a gas. The air just carries away the liquid vapor. Water vapor is still water at low enough temperature to form temporary (liquid) bonds. As the air carries away the water molecules it also carries away their heat.

Carries away their heat? How do you mean?

Evaporation causes cooling. We use it all the time to cool down when we have been working hard.

You mean we sweat.

Yes. Perspiration is water that our body dumps onto our skin as we try to cool down. Those warm water molecules are easily picked up by the air as a vapor. The air carries away those warm water molecules leaving behind a cooler body (and some salt). Water is the only molecule we can make (in large quantity) which easily goes into the vapor phase. There are other liquids you can use to cool down people or machines.

I don't care about these "machines" you keep talking about, but what about people? What other liquids can you use to cool people down?

Alcohol.

I thought you were talking about cooling people down not firing them up!

Very funny. I'm talking about using it on the skin, not the mouth. As a matter of fact, it is best to use an alcohol that is NOT FOR DRINKING. Most people call it rubbing alcohol. Because you rub it on your skin to cool down.

But if you drink it, it will rub you out! Ha Ha.

Yes, it will.
Use a piece of cotton to wipe water on the back of one hand and alcohol on the back of the other. Do this FAR AWAY FROM FLAMES!

OK! OK! Far away from flames. Then what?

Wave your hands gently in the air. You will feel that the hand with alcohol on it cools more than the one with just water.

Why is that? They are both cooling because of evaporation, right? So both liquids give off vapors into the air. Both water and alcohol cool the same way - by evaporating.

Yes, they do, but not with the same efficiency. Alcohol molecules are larger than water molecules, so when an alcohol molecule evaporates it carries more heat away with it. Therefore the hand with alcohol on it cools faster, because alcohol vapor removes the heat better.
Also, alcohol evaporates better than water. We say alcohol is more volatile than water, meaning alcohol more easily takes to the vapor phases than water does.

Is evaporation useful? I mean other than for cooling down bodies.

Oh, yes. You can use this "trick", called evaporative cooling, to cool a tent. Just sprinkle water on it! You can even use it to keep food cool (for short periods of time). Just drape a wet towel over the basket of food and set it in the shade. As the water evaporates, it carries away the heat.

I mean other than cooling. What else is evaporation good for? Do Alchemists use it?

Yes, on occasion we do. Most table salt is made by evaporation. In salty water, both the Na+ and Cl- ions are surrounded by solvation shields.

So they can't get together to form table salt (NaCl).

Right. However, as the water molecules evaporate they leave behind salt molecules. As time goes on, and more air sweeps away more water vapor, the solvation shields start to break down. There are just not enough water molecules to keep the ions away from each other.

Then electrostatics brings the ions together. Forming NaCl. Simple.

Aye. These easily grow into crystals of NaCl - crystals of table salt. That's how table salt is made by evaporation.
Do This! Put some warm water into a glass and add as much table salt as you can, until no more will dissolve in it. Stir it to help the salt dissolve. When you can't dissolve any more salt in the water, you have a saturated solution of salty water.

Then what?

Nothing. Just set it aside to evaporate. You don't need to put it in the light. Just leave it out where it can get lots of air. Eventually, the water will evaporate and leave behind the salt crystals you put in it.

Would it evaporate faster if I poured that solution into a wide bowl or even a plate?

Good question. What do you think?

Gee I don't know. You're the teacher. You tell me.

No. I teach. You think. You tell me.

OK. I think it would help to use a plate to hold the evaporating solution.

Why?

Evaporation has to do with giving the air a chance to pick up the water vapor. The water in a shallow bowl or plate has more contact with the air than if it was in a deep glass. More air will be able to sweep past more water if the solution was in a flat plate than if it was in a deep glass.

Absolutely correct. As a matter of fact, we Alchemists use special glass or porcelain "plates" just for that purpose. We call them evaporation dishes, but any dinner plate will do.

Evaporation is kind of like a lazy man's distillation, isn't it?

Sort of, but remember that distillation requires you to raise the temperature up to the boiling point (of one of the liquids). That's because distillation IS boiling! You must make a gas for distillation. But evaporation ...

... is just the air carrying away the liquid below it's boiling point. I know. But the final result is the same. You get salt crystals.

Well, in this example you do get the same result. However, I don't want you to think that you can substitute evaporation for distillation all the time. Those two methods depend on two different things. Distillation depends on the chemical's boiling temperature, but evaporation depends upon a chemical's vapor pressure.

What's vapor pressure?

Without going into details, let's just agree that vapor pressure is a feature of each liquid or solid, a measure of how well they evaporate. For example, alcohol has a higher vapor pressure than water. Alcohol is more volatile.

So alcohol is more volatile than water. Like you said earlier.

Right! Sometimes it is best to use evaporation, especially if you want to grow pretty crystals.

That's because it takes time to grow crystals. The molecules need time to line up. And evaporation takes a long time.

That's right. Very good. Evaporation is a long, slow process. So it is perfect for growing crystals from solutions.
However, sometimes we want to separate liquids based upon differences in boiling points. That's when the best method is distillation.

I get it.
Crystals are pretty easy to grow. Aren't they?

That depends on the kind of crystals you are trying to grow. There are lots of easy ones you can make at home. All you need to do is add lots of a salt (not just table salt) to water. Dissolve the salt to release the ions and let the water sit quietly.
Mother Nature was making all kinds of crystals long before Alchemists. Have you ever been inside a cave?

No, can't say I have.

Well, they can be dangerous places. You don't want to wander around in a dark cave. Might fall down a shaft. Anyway, some caves contain long columns of crystals produced by the evaporation of water as it dripped, and continues to drip, through the roof. This water is often full of sodium (as a cation) and carbonate (as an anion). At the tips of the hanging drops, evaporation occurs and the solvation shields break down. What do you think happens to the sodium and carbonate ions?

I don't know. All I know is that carbonate is an anion, like you just said.

That's all you need to know. What happens?

I suppose once the solvation shields fall apart, the sodium cation and carbonate anion are drawn together by electrostatics. They form a compound of sodium carbonate.

Yes, that is exactly what they do. The sodium carbonate precipitates out of solution forming crystals. Over thousands, even millions, of years these tiny crystals build up a stalactite, a long, thin column of mineral hanging from the ceiling of these caves. Some of it drips on the floor to make a column called a stalagmite. They are very pretty works of Nature created by evaporation.

I am NOT going into a cave to see these stalactites and stalagmites. No way!

Well, someday you may visit these wonders and I hope you will appreciate that they took a long time to make. It is easy to understand how they are made. If you haven't the time or desire to visit a cave, you can make your own stalactites.

How?

Do This! Fill two glasses with warm water that is saturated with sodium carbonate (NaCO3, sometimes called "washing soda"). Get a piece of string, about a foot long. Wool string works best. Tie a paper clip or bolt to both ends.

I don't have paper clips or bolts. Can I use small rocks?

Yes, (but they are more difficult to tie with string). Put one end of the string into one glass and the other end in the other glass. If both glasses are full of solution, the string (especially if made of wool) will suck up some of the solution. Allow the string to droop a wee bit between those two glasses of warm, saturated sodium carbonate solution. To keep things clean and tidy, place a plate underneath the wool to catch the drips. Then leave it alone.

So we wait, like we did for the salt evaporation we did earlier.

Yes. Water evaporates from the string, leaving behind crystals of sodium carbonate. As the days go by, a small, white stalactite grows down toward the plate. You might even get a stalagmite to grow upward from the plate.

This same thing goes on in certain caves all the time?

Aye, and it has been going on for millions of years. But you can make a few small stalactites for yourself in just a few days.


This work was created by Dr Jamie Love and licensed under a Creative Commons Attribution-ShareAlike 4.0 International License Creative Commons Licence.