Program 22 - "Classification and The Properties of Matter"

 

MusicSilico: "We are back with Science 122, The Nature of Physical Science.Where we give a definitive answer to the question, "What is the matter?"This is Program 22, Lesson 3.7, Matter and its Properties."Before we're done with this program we will have answeredthe question, "What is Matter," as we distingishbetween substances and elements and learn about atoms and elements.We'll learn how matter can be classifiedand we will learnabout the physicalcharacteristics of the states of matter beforewe study chemical and physical changesand the energy involved in chemical reactions.We'll conclude with a brief description of the science of chemistry and its goals.Here are the objectives for today's lesson.These objectives are also in the Study Guide at the beginning of the lesson.Before you begin to study the lesson, take a few minutesto read the objectives and the study questions for this lesson.Look for key words and ideas as you read.Use the Study Guide and follow it as you watch the program.Be sure to read these objectivesin the Study Guide and refer to them as you study the lesson.Focussing on the learning objectives will help youto study and understand the important concepts.Compare the objectives with the study questions for this lessonto be sure that you have the concepts under control.

 

Now we turn our attention to the study of matter.The study of matter is as old as the study of the stars.We talked earlier about the fact that astronomy was the oldest science.Well, if that's the case, then man's manipulationof matter is certainly the oldest technology.Everything from the chipping of stone tools to the useof fire for smelting metals from their ores,for firing pottery, isolation of specific chemicalsfor dyes, medicines and toxicants, and also, for food.The act of cooking is actually a technologywhich involves the manipulation of matter.Our modern world knows tens or maybe evenhundreds of thousands of different substances.Each substance has a unique set of properties.So the discoveries of these components of matterand their properties is a story which will occupy our effortsfor the remainder of the course as we trace the developmentof the atomic paradigm from its beginnings way back at the beginning of time.Along the way we'll see how the Newtonian paradigm is usedto help in the discovery of atoms and their properties,and also the composition in nature of the atoms and the matter that they compose.This will lead us to the modern atomic theory.

 

All of us have grown up with the atomic paradigm so it's hardfor us to imagine a world where people didn't believe in atoms.But, it was only up until, it was only this century, the 20thcentury, that people actually believed in the existenceof atoms, and after all, how many of you have actually seen one?So, what we're going to see here, the sort of the themeof Section 4 here, is, that we'll start in the next program isto provide a connection between chemistry and the Newtonian paradigm.The Newtonian paradigm, it turns out, can be used to explainchemical, physical and thermal properties of matter,and what it really does is to unite all of physical science under one paradigm.So what is matter, anyway?This should be an easy question to answer.Everybody knows what matter is.We usually know it when we see it.But it's hard to define, even though it might be easy to recognize.So, certainly, when you see it, you can tell what it is, can't you?Let's look at some examples and see if we can tell what's matter and what isn't.Is air matter?Of course, it is.Well, at least we think it is.We can feel it.It has substance.How about clouds?Even if we can't touch clouds, we know that they're things.They're stuff.They're made out of water.How about iron?Sure, iron's matter.It's hard.How about water?Sure, water's matter.But what about these other things?What about thoughts?Are thoughts matter?What about ideas?And how about emotions?These last three things are definitely not matter.What's different about them?Well, let's define at this point, simply to say thatmatter has mass and occupies space.This may not be a very satisfactory definitionif we don't know what space is, but we do know what mass is.So, maybe we can say at this point that matter is thatwhich obeys Newton's laws.

 

So now we know that matter has mass and occupies space,but what does it mean to be substance.The word, substantial, means or comes from having substance.But, still, what is it?We might say that it's actuality.Like in the statement, "It was only a dream."Without substance.So, we might say that a substance is a particular kind of matter,and each substance has unique properties whichdistinguish it from other substances.We want to also note here that some substancesare elements, but most substances are not.In fact, those substances which are not elements are combinations of elements.So, then we then can think of elements as a specialclass or special category of substances.In the same way that we think of a substance as sortof a refinement of the concept of matter.The concept of atoms and elements is one that we takefor granted today because we associate the two things here in our atomic age.

 

The concept of elements and atoms have been joined.In fact, they are actually separate concepts that weren't broughtback together until the 17th century.But let's look at these things for a minute.Elements are the purest kinds of substances.These are substances which contain only one kind of atom,and pure uncombined native forms are very rare in nature.Some things do occur naturally, but most things occur asmixtures, like air in the atmosphere or waterin the sea, or as compounds, things like water, itself,or most of the things that we find around us.Only a very few elements occur in nature uncombined.One of these is sulfur--the yellow stuff.Metals, like copper and zinc and gold and silver, and nonmetals like carbon.But there are actually very few of these that do this.Oxygen and nitrogen, for example, in the air are uncombined,but they're so well mixed that we don't separate them outnormally and we don't see them separately.

 

The Greeks from the time of Democritus on,this is pre-Socrates, considered atomsand elements as separate concepts.It's hard for us to get a picture of this becausewe tend to link these two things together.But, the Greeks rejected the concept of atomsfor reasons that we'll see in the next program.But, they kept the idea of elements.And what they kept was Aristotle's conceptof elements, the four elements of earth, air, fire, and water.So, our modern concept of element as specific substances likecopper and zinc and iron and so forth, has a very long and complicated evolution.From Aristotle's four elements, earth, air, fireand water, through the mystical elementsof alchemy; things like sulfur and mercury, which,some of which are considered elements today, but not all of them.So, as we go through our story of the developmentof chemistry, we'll see that more and more thingswere isolated which were considered to be elements.In fact, in 1500, there were thought to be only nine elements.These were again, things like mercury, and sulfur and iron and various metals.In the mid-1800s, about 350 years later, 50 differentsubstances were known to be elements.A hundred years ago, at the end of the 19th century,80 to 85 elements were recognized, or substanceswere recognized as elements.

 

Today we recognize about a hundred, little over hundred things as elements.So, the number of things we recognize as elements isgrowing rather than shrinking.We think, today, that we understand all of the things that are elements.So, maybe we can think of it this way.Connecting the elements with the fundamental particles of matterthat we call atoms is a modern concept.And it's actually a synthesis of two previously unrelated concepts.And it's very interesting that up until the 17th century no onereally made the connection between these two things.The concept of element was well established, but the marriageof the two concepts, atom and element, requires a special consideration.That's the subject of Section 4 of the course.And really what happened was that it required a newdefinition of both the concept of atom and the conceptof element, and it was a very important step in modernthought, especially in the development of physical science.But now it's time to turn our attention to the classification of matter.It's important to be able to classify matter into varioustypes which we'll do, and you might notice that the textbooksgive slightly different classifications.But that's all right because there are many different ways to classify things.We want to look at matter in terms of bothheterogeneous mixtures and homogeneous.

 

So let's look at heterogeneous first and we'll consider eachone of these in turn and define them as we go along.So, heterogeneous mixture is also known as an aggregate.Does anybody know what an aggregate is?Well an aggregate is simply a heterogeneous mixture.I know that isn't very satisfying, but anaggregate is something like concrete, for example.When you make concrete you mix the cement with an aggregatewhich consists of sand and gravel.It helps to hold it together.The concrete, itself, is called an aggregate material.So we can define a heterogeneous mixtureas a mixture which can be physically separated.When we say physically separated, we don'tnecessarily mean that it's easy to do this.We just mean that we can do it because we're ableto pick out the individual constituents.In other words, when you look at the concrete you can see the gravel.You can see the sand.You can see the cement, even though it may take yousome time to pick the things out.That's not the point; the point is that they can beseen and that they can be separated.Some examples of heterogeneousmaterials--sand on the beach.You pick up a handful of sand, you'll see that it'smade up of many different kinds of grains.I already mentioned concrete.A chocolate chip cookie.

 

Now in principle you can see the chocolate chips and you couldpick those out of the cookie if you wanted to, although,I don't know what you'd want to, but, you could if you wanted to.OK, so that's heterogeneous mixtures.Let's look at homogeneous.First of all, the word, homogeneous, the homo means same.So we're looking now at homogeneous mixturesof two types which are basically mixtures whichyou cannot see the individual constituents.So the first one we want to look at is a homogeneousmixture known as a solution.I think everybody knows what a solution is, right?A solution is dissolving one thing in another.And, ordinarily, these can be separated by physical means.By physical means we mean not chemical means,and to understand that distinction, we'll have to waittill we get to that section of the program today.But, again, this may not be easy to do, but, for example, if we wereto dissolve sugar and salt together in the same jarwith water, we could, in principle, separate them outby crystallizing them at different temperatures or by evaporating the water.

 

Even mixtures of things like water and alcohol can be separatedSo, what characterizes a homogeneous mixture is thatthe individual constituents cannot be identified.If you just look at a glass of salt water, you don't see the individual grains of salt.Or, if you take water out of the ocean you don't seethe salt in the ocean, but it's still there.OK?You can't identify the constituents.I should say you can't identify them by sight, you can certainlytaste the difference between salt water and regular water,but you can't identify them by sight.Some examples, many things that we use aroundin everyday life, sea water, for example, I alreadymentioned; perfume is a very complicated homogeneousmixture of essences and alcohols and various things.And even the air we breathe is a mixture of many differentgases, oxygen and nitrogen, carbon dioxide, argon, and so forth.OK, so that takes us now to pure substances.And pure substances, as you might suspect, are thosewhich only contain one kind of thing.But we still have to classify this furtherinto two different types of materials.That's compounds and elements.So, let's look at compounds first.A compound is simply a substance which contains only one kind of molecule.

 

Now at this point in our study of physical sciencewe have yet to define what a molecule is.In fact, we're working up to that.But for now, let's just say that a molecule is aparticular combination of atoms.For example, a water molecule consists of twohydrogen atoms and one oxygen atom.A carbon dioxide molecule, CO2 consists of one carbon atom, two oxygen atoms.So, at this point, even without knowing whatatoms are, let's use this as a working definition.So, examples of compounds are water, alcohol, carbon dioxide.Now pure water, of course, consists only of H2O.In reality, most of the water that we drink and areexposed to contains other things.It's either a solution or a mixture.Some of this is pollution, some of it is simply natural ingredients.These three things are all compounds.So, our final category is that of an element.An element is, you might think of this as sort of the ultimateform of purity as far as substance goes.The element is the substance which contains only one kindof atom, as opposed to a compound which contains only one kind of molecule.So, examples of things that contain only one kind of atom is oxygen.

 

Oxygen is a substance which consists only of oxygen atoms,and copper, the metal, consists only of copper atoms, and carbon.You've probably heard some of these names of theseelemental substances before, and we will spend some timein later programs coming back to these and examining themin the context of the periodic table and, even today,little bit in context of some of their properties.Now let's turn our attention to the states of matter.We discussed this the last time,in a previous program, anyway, when we lookedat heat transfer and heat exchanges in latent heat and changes of state.

 

 

 

 

Specifically we want to look at the properties of eachof the three states, gas, solid and liquid, because eachof them has their own unique properties.So, let's go to the gas first.The gas has a specific relationshipbetween temperature, pressure and volume.I can demonstrate this for you on the ELMO, but before we do this,I have to put my gloves on because we're goingto be using some very cold stuff.Hey wait a minute, I've got two left gloves here.Did we do this two left glove thing already?I don't know.OK, let's go to the ELMO.So what I've got here is a balloon that's full of air, like the rest of us.And I have in the container here some liquid nitrogen whichis about 190 degrees below zero Celsius.What I'll do is pour the nitrogen on to the balloon and watchthe balloon shrink as it becomes colder.You can see that pouring the liquid nitrogen on to the balloon,the balloon gets smaller and smaller and smaller,in fact the air inside it almost completely disappears.Now if I let that sit there, as it warms up,you'll see that it will gain back its temperatureand also as it warms up, will refill again.

 

Now obviously, there's no change of the amount of air inside.What's happening is the air is simply compressing and changing its volume.OK.So, let's go and review the properties of the gas very briefly.So the gaseous state of matter is characterized by a specificrelationship between temperature, pressureand volume, but specifically, we can characterize the gas as asubstance which has a variable shape; that is, it will expandto fill any container, and at the same time, has a variable volume.In other words, regardless of the size of the container,it will expand to fill the entire container.OK, so a gas we can think of in terms of variable shape and variable volume.So much for the gaseous state.The next state that we want to consider is the solid state.Now most solid substances are crystalline.Crystalline means that they have an orderly repeating crystalstructure like this model of the zinc sulfide, a mineral called sphalerite.This is called a crystal lattice.

 

Now in principle all solids were allowed to grow freelywithout being restricted, they would grow a nice crystal shape.But the crystal shapes are not always apparent.Most things that have a crystalline structure havea fixed melting point for a given substance.I have some crystals here.Let's go the ELMO and take a look at some of these crystals.I have various types of crystals here.Here's a couple of quartz crystals, actually threeof them, and there's a crystal of pyriteand here's another one of quartz, and a crystal of calcite.Now notice the shape of these things.The quartz crystals all have a particular shape which reflectsthe internal orderly arrangement of their atoms.There are other substances that are not crystalline thatwe consider to be solid, although they strictly are not.These are things that gradually soften over a temperature rangeinstead of melting at all one temperature.Things like glass, tar and butter, they become progressivelysofter as the temperature increases, rather than, simplymelting at a particular place like the crystals do.

 

Let's see how we can characterize the solidsin the same terms that we did with the gas.The solid state we can specify as being fixed shape.In other words, you could leave a solid substancearound, it doesn't change its shape.You come back the next day and the couch is still a couch.It also has a fixed size or a fixed volume.So, if you have a block of iron sitting around,you come back the next day, it's the same size.Unlike a gas, it does not expand to change or to fill up the entirespace, nor does it take on the shape of the things around it.The third state of matter we want to consider isprobably the more common, that's the liquid.Only water is the naturally common liquid on earth.In fact, for the most part, liquids are very rate in the universe at large.Here on earth we just happen to live on a planet where thetemperature and pressure conditions are right for liquid water to exist.Most other liquids that we find here on earth are eitherman made and even if they are, they're water based.But, we, ourselves, are largely a collection of water.

 

We're about 90% water or something like that.So, we can think of this as, oh, you know, I think it's timeto get rid of this glove, I don't really need this glove,I don't need to do the Michael Jackson thing here.So, if solids are represented by a organized collection of atomsin a crystal structure, and gases are represented by a completelychaotic random, what do you suppose liquids are?Liquids are somewhere in between.In fact, in liquids the atoms sort of align themselves in shifting groups.You know, sort of like cliques in high school where they sortof connect with each other for a while and they keep shifting around.

We'll come back to this more in detail when we study kinetic theory.But for now, we can think of the liquid state asa chaotic or sort of semiorganized state.So, let's go now and characterize liquidsin the same terms that we did gases and solids.

 

A liquid can be thought of as a substance which has a variable shape.In other words as you pour it from container to container,it takes on the shape of the container, but unlike thegas, it maintains a constant volume.So, a cup of water is still a cup water, even if it'sin a large glass or a small glass.It does not, like the gas, expand to fill its container.Another state of matter which is sort of in between a liquid and asolid, which is very important to us both in the personal basisand industrial basis in our modern society, is that of liquid crystals.Liquid crystals are substances which are normally sortof a glassy state, meaning that their individual atoms are notparticularly aligned, but they're very tenuously not aligned.What that means is that they're ready to be aligned and all theyneed is a little bit of a disturbance to align them.I think I can show you an example of this when we go to the ELMO.Here's a liquid crystal plate and it looks just like a blackbackground, but it's very sensitive to temperature.So if I put my finger on it, the temperature of my finger is alittle warmer than the liquid crystal and you see that whenI take it off, it leaves aninterference pattern.This pattern is actually disrupting the atoms and moleculeswithin the liquid crystal and producing an interferencepattern much in the same way that an oil slick produces aninterference pattern on a wet street.Notice it very quickly goes back to its normalequilibrium state once its been disturbed.

 

So liquid crystals are useful for all kinds of things.In this case they can be used for things like diagnosis of tumorsand other physiological conditions which were,part of the body produces excess heat.And tumors usually are a little warmer than the surrounding area.We also use these a lot for displays,for example, on watches and calculators.Everybody's seen this.The interesting thing about this is that here the disturbancein the glassy state of the liquid crystal is being causedby electricity or by an electric field, the light is actually polarized.If I put a polaroid plate in front of this you can see that as I turnit, it cuts out the light from the watch.So it doesn't allow the light in.In fact, the crystals, liquid crystals inside the watch arealready polarized and we see them because there's a cross polariodplate in there which blocks the light from those portions wherethe crystals have been activated.

 

Let's first take a look at the physical properties of matter.Physical properties are those properties of matterwhich are distinguishable with the senses.That is, things that we can taste, smell, see theshape of, and otherwise use the senses.Now the physical properties are both qualitative and quantitative.Meaning that some things like tastes and smelland shape and color and luster, you know the wayit shines off the surface, are qualitative, and it's veryhard to describe to someone exactly what colorsomething is or exactly what it tastes like, or exactly what it looks like.On the other hand, are other properties which are much more quantitative.Things like density, thermal conductivity, thermalexpansion, electrical resistance, specific heat,boiling and melting temperature, cleavageand crystal forms of minerals are all quantitative.These are the things that we can put a number toand we can describe very precisely.So, what I'd like to do is to demonstrate a coupleof these physical properties for you.Let's go to the ELMO to do that.The first property I want to demonstrate has to dowith the internal arrangement of crystal.This is a property called cleavage and this simply relatesto the tendency for crystal to split along certain flat planes.What I've got on the screen is a piece of calcite.This piece of calcium carbonate whose crystal structure formsit into this sort of rhombohedral shape.

 

What I want to show you is that if I put a chiselin here and tap this with a hammer, that when thecrystal splits, it splits along this perfectly flat surface.I wouldn't say it's perfectly flat, but it's relatively flat.Notice that no matter how many times I do this...I think if I try to cut across the grain...OK, can I do this?And when it breaks into tiny pieces, each little tiny piecestill has that same characteristic shape.Notice how each one of those little pieces still has thatcharacteristic rhombohedral shape of the other crystals.So, what we're seeing here is a reflectionof this internal orderly arrangement of the atomsand molecules which make up the calcium carbonate crystal.The other physical property I want to show you hasto do with the freezing of liquid mercury.I'm going to use the liquid nitrogen again,but the liquid nitrogen is wasting away very fasthere, so let's go to the ELMO before we lose it all.In the beaker here I have a little bead of liquid mercury.You can see it rolling around here, very definitely a liquidWhat I want to do is to just put a nitrogen on topof it and see what happens when it stops boiling.Let's see what happens here.Pour this in here.

 

Notice the nitrogen boiling and the reason it's boiling,of course, is because the mercury is very hot comparedto the temperature of the nitrogen, so is the glass beaker.But I think you'll see that it doesn't take very long to freeze the mercury.In fact, let me pour the nitrogen out, pour it back into the cup.I think the mercury is probably already solid.And what we've got here is now a solid piece of mercury.Notice that as soon as I touch it with the chisel, it melts.But notice, it's very solid.(Tap, tap, tap.)So what we're seeing here is simply the fact that even asubstance like mercury which normally is liquid at roomtemperatures, does have a boiling temperature and freezingtemperature, and liquid nitrogen, very cold,190 degrees Celsius below zero.So if I do this with the nitrogen in there,the mercury is completely solid.It's really neat stuff, actually.It sort of has the texture of bubble gum at this point.But it's certainly not a liquid like it was before, very, very solid stuff.

 

So the next thing now is to take a look at the chemical properties of substances.This is really hard to describe unless you can see it.So what we want to do is to show you some of thesedemonstrations of how chemicals behave with other substances.That's what chemical properties is about.It's about chemical behavior of one substance with another.But before we do that, I think it's time for my afternoon constitutional.Let me do this.I'm sorry to do this on camera, but...OK...that ought to be good.I do this every day just, you know, helps keep me strong.(Swallow, swallow, swallow, umm.)Oh, that's good.(Sign.)OK, I'll have some more of that later.So, let's take a look at the video that we saw at the beginningof the program one more time and then I'll come back and showyou something about that on the ELMO.That video was a time lapse picture of a chemicalreaction involving copper and silver.The solution that I had was the solution of silver nitratewhich I put into it a piece of copper.You'll notice here the copper, if I pull this out, is corroded.The stuff clinging to it on this side is actually little crystals of silver.I can clean those off and you see what the copper looks like.I won't clean it off, but you can see how the copper's corroded.

 

The corrosion on the copper is from the fact that what'shappening here is that the silver in the solution is coming outof the solution and turning into silver while the copper, itself,is dissolving, turning the solution blue.Can you see the, how much the copper's been corroded here?See the difference in size of the different parts of the plate?So, the other thing that's interesting now is that oncethe copper's in solution, I can take a piece of zinc and put the zincinto the copper solution and copper should startto appear on the surface of the zinc.Notice the color of the zinc is kind of grey.What's happening here again is another type of reaction wherethis time the copper that's already been put in solutionfrom the silver nitrate is going to start to collect on the zinc.And once again, I hope this happens quick enoughfor me to be able to show you what happens.The copper is not starting to go on the zinc.I think what I want to do is, I'll put this aside for a minuteand go on to the next demo, and we'll come backand see what that looks like in a minute.

 

The next thing I want to do here has to do with the metal we know as sodium.Sodium is a soft metal and it's so reactive that we have to keep it under kerosene.So let me take a little piece of the sodium out of here.I'm going to cut this on the paper.What I'm going to do is cut this into little pieces.Notice it sort of looks like a cracker or like a tempura thing.I going to take this.I'll put the rest of it back into the container.Notice the sodium, itself, is so reactive again, even under thekerosene, you have to keep it...it sort of corrodes.This is a very interesting reaction.So, stand back, guys.OK, I'm going to just drop the sodium into the water.

 

 

 

 

Now ordinarily water is, we think of it as asemi-corrosive substance, but along with somethinglike the sodium, it's pretty amazing.Let's see what happens.Notice here that the sodium is reacting very violently with the water.And sometimes it even throws off a little yellowflame, and sometimes they even explode.So what's happening here is that the sodium is actuallyundergoing a chemical reaction with the water wherethe sodium is reacting to become sodium hydroxide and leavingbehind the residue of sodium hydroxide.Now you see that when the whole thing's done,all that's left is these little pieces of corrosion.There's some sodium left in there.The little bubble you see floating around is actually a piece of melted sodium.This reaction generates so much heat that it physically meltsthe sodium and turns it into a molten ball of sodium dancing around.I don't know if the zinc has actually doing anything yet.I don't you can see this on the ELMO.Let me put it back in here.I don't think you can see the color of the copper.I can see there's a little bit of red.If I zoom in on this, you can probably see some of the copper sticking to it.I don't know whether you can actually see that or not.Oh, a little focus would be nice.There we go, see the little beads of copper there?Little red beads.Here's some.So these little red beads of copper are the coppercoming out of this solution of the copper nitrate.

 

Another chemical property is the reaction of a substance with acid.So I want to dissolve a couple of things for you here.So, since I'm going to be using acid, I'd better put the glove back on again.And I've got a couple of bottles of acid sitting over here.There's a bottle of hydrochloric acid.And there's a bottle of sulfuric acid.So let's go to the ELMO and see what these acids dowhen I pour them on to things.In the container here I have a, some zinc chips.I'm going to pour the acid on to the zinc and we should be ableto see a reaction almost immediately.See the bubbling of the acid?What's happening here is that the zinc is reacting with the acid.A chemical reaction is going on here wherethe hydrogen in the acid is replacing the zinc.This is very similar to what happened with the copperand the silver except that it's a little more violent.It looks more violent because what's beingreleased here is hydrogen gas.

 

The hydrogen gas forms from the hydrochloric acid.OK, in this beaker I have some marble chips.Marble is a form of calcium carbonate which is very reactive with acids.So when I pour the acid in here, this one's going to startfoaming and bubbling, and again, this is a different kind of material.This is a nonmetal, but it's still a substance which reactsvery abruptly with hydrochloric acid.This particular reaction produces carbon dioxide.And so, carbon dioxide, as you know, is a flame retardant,so when if I put a match in here, you see the match go outalmost instantly in the carbon dioxide.It's almost like dipping it into water.It simply does not support combustion.This, by the way, is the kind of thing that Joseph Black wasplaying around with, with carbon dioxide when he discoveredthat it was given off by any sorts of reactions.Notice that it snuffs out almost immediately.OK.

 

The third thing I want to show you has to do with sulfuric acid.Sulfuric acid and sugar reaction is really an interesting one.Sugar is basically water and carbon combined together.The sulfuric acid has quite an affinity for water, and whenyou pour it on to the sugar, it sucks the water out of the sugar quite violently.It might take a minute for this to get started.You notice that the sugar is slowly turning color?What's happening here is that the sugar is basicallybeing converted to carbon by the sulfuric acid as theacid literally sucks the water out of it.I used large crystals of sugar this time instead of finelygranulated sugar because if you do it with finely granulated sugar,it sometimes doesn't explode, but it sort of wells up outof the cup and drops the sopping sulfuric acid all over the place.You notice the color of it as it turns now, getting more and more carbonated.If I add a little more sulfuric acid to it, I think it might go a little faster.And I don't think we want to wait for it to turncompletely black,but it will eventually.As the sulfuric acid literally decomposes the sugar,takes the water out of it and leaves behind the carbon of the sugar.Again, all of these are chemical reactions with various kinds of acids.

 

The last chemical property I wanted to talk about is that of combustibility.Everybody's seen something burn and we know what combustibility is.But usually we think of this in terms of paper and wood and organic products.It's not very often that we see a metal burn.So what I have here is a piece of magnesium.The magnesium is a metal which burns at a fairly lowtemperature and gives off an extremely bright white light.In fact, it was used in the early days of photography as a flash powder.You've probably seen this in old movies.The person with the trough of some powder and he lights it.So what I want to do with this.First of all notice it's metallic.It bends, has all the properties of a metal.What I'm going to do with it is burn it.So, let's burn it.To burn it, I want to use the torch.I'll get the torch lit first.And this is a fairly bright light, so I want to make sure I don't burn my eyes out.So I'm going to put this thing into the flame.It shouldn't take too long for it to start and watch how bright this is.Watch the brilliant white color.This is also used sometimes in flares for obviousreasons, for signal flares and so forth.Shouldn't take very long to get it started.Look at that.Ever see a metal burn like that?Imagine those magnesium wheels on your car when they go up in flames.We don't usually think of a metal burning like that,but here again, it's a simply a reaction of something with oxygen.When it's done, I turn the torch off.Can we zoom in on that again, and get a close up?Notice the white ribbon left?The white ribbon there is magnesium oxide.And if I notice before, it was metallic and now it's crisp.It's basically ashes.The ashes are magnesium oxide.

 

Now it's time to consider chemical versus physical changes.This is related to the ideas that we looked at before in termsof the properties, because after all, it is the physical propertiesof a substance that are involved in physical changes.The problem that Aristotle and his contemporaries, in fact, earlychemists and alchemists had in many cases was failingto distinguish between chemical and physical changes.So it's important for us to get a little bit of a handle on the difference here.Most of the time the changes can be clearly identified by oneor more of these following criteria that we'll talk about.But, generally no particular one criteria is sufficient to decidewhether a change is chemical or physical.Sometimes it's obvious, sometimes it's not.So, of all of these that we're going to see, only the fixedratio method is both necessary and sufficient to distinguishchemical reactions from physical.But, unfortunately, it's also quite difficult and it requires,in many cases, very precise chemical experiments to perform.So let's look at some of these criteria to decide whethersomething is a chemical or a physical change.The first of these is reversibility.

 

Reversibility simply means that once a reaction is done, it can be undone.So, physical changes for example, are generally reversible.And generally, or very often, at least, are reversible by thermal processes alone.For example, ice melts to water.It gives off the latent heat, the water carries the heatwith it, the water evaporates into steam.You cool the steam down, it changes back into water.You cool the water down, it changes back into ice.You can do this time after time after time without losing any of the water.Right?Simply by putting the water into the refrigerator or on a stove.The same thing is true of salt dissolving in water, for example.You can put salt into water.You can evaporate the water out, you get the salt back.You put more water in, the salt dissolves.You evaporate the water, the salt comes back.So, all of these things are physical processesand specifically are reversible physical processes.So, as far as chemical changes go, chemicalchanges are generally not reversible.You can think of it this way.If you take an egg out of the refrigerator and put itinto a pot of boiling water, you cook it.When you put it back into the refrigerator, it does not uncook.Right?The egg, once cooked, stays cooked.So, generally chemical processes are notreversible, or at least, not easily reversible.There are, however, some chemical processes that arereversible, and easily reversible.In fact, many things like, for example, the smeltingof iron is a reversible chemical process.

 

Iron rusts, we can take the rust and turn it back into iron.It requires some fairly extensive chemical processing to do this.But some of these things are very easy to do, and I can do some for you here.Let's take a look here.I have here some indicators which are used for indicating acidity or pH.This particular one is a combinationof a substance called phenol red and thymol blue.What I'm going to do here is to take a few drops of thissubstance which is sodium hydroxide, it's a very strongbase, and drop it in here and watch what happens.Notice that a few drops of that swirled around,what formerly was orange, becomes blue.OK, this is an indication, this is a particularchemical that's designed to do this change.Actually I said blue, if you look at it in the light,it's actually sort of a reddish color.So, this is a chemical reaction that takes placewhich changes the color of a dye.In this case it's specifically designed to be reversibleso that you can use this to determine whether asubstance is acidic or basic.

 

So, now I have some hydrochloric acid.I'm going to drop the hydrochloric acid into here.It might take quite a few drops to do this.Keep doing it until it begins to change color.If that doesn't work, I'll drop some really concentrated acid in.There you go.I'll swirl it around and magically the orange color reappears.I can do this as many times as necessary.I can put a drop of the sodium hydroxide in and it will change back.If I get enough of it, anyway, it will change backto the red color, and I just have to over-titrate this I guess.So, you can see as the drops of acid go into it, how it changes back to the color.It take quite a few drops, I guess, to get it back completely.But I can keep doing this and eventually it will,all of a sudden, actually, it will change back into the red color.Every time I put a drop of it in, the red comes back a little bit.There it is.Swirls around, you can see how it sort of mixes.Here the other indicator I have here is somethingthat I'm sure everybody's heard of.We use the word, litmus test, a lot.You know in a sort of general usage.The solution I have here is a solution of a substance called litmus.Litmus has the property that it changes from redto blue and back again at a pH of neutral.In other words, a pH of 7, which is the neutral pH of water.If you don't understand all this stuff about pH, don't worry about it now.

 

We'll come back and learn about this a little bit later on.But, the point here is simply to watch how the chemical changes take place.So, if I take this hydrochloric acid and drop a few dropsin there, I should be able to see the solution change to a reddish color.Isn't that amazing?You can do that.And then if you take a few drops of the sodium hydroxide again,and drop this in, it changes magically--well, maybe notso magically, magically, but not quickly, back to blue.Again you can see the blue color appearing in there.I don't know, gee, we maybe running our of sodium hydroxide here.I may have overdone this a little bit.But you can see the blue color reappearing as I dropthe drops of the base back into it.OK.I guess I really overdid it with the acid.But you can see again, when I put the drops of sodium hydroxidein, you'll see the blue color reappearing.I think I hit it that time.So the solution now switches back to blue.So this is an example of a chemical reaction that is reversible.So, the next aspect here then of chemical versus physicalchanges is the idea of thermal processes.Now this is a tough one because chemical changes give offand absorb heat, and we'll examine that a little bit laterin the program, but so do physical processes.

 

We know already, for example, that when icemelts to water, heat is involved.In fact, when steam condenses, heat is given off.So, although this is a criteria, you have to understand very clearlywhat's going on with the processes themselvesbefore you can really use it as a way of deciding whether or notsomething is a solution, I should say, is a chemical reaction.Generally what happens.We can think of two specific examples and I'll show youexamples of one of these later.We've seen one already.Is that solutions become warmer or colder whenyou dissolve something in water.With ordinary table salt it's not much, but I'll show you a littlelater a couple reactions that really do produce heat.The other thing is combustion.We already saw combustion of the magnesium ribbon.Of course, we know that combustion gives off heat,so generally, if something gives off large amountsof heat, there's a chemical reaction involved.If it gives off small amounts of heat, it's a physicalreaction, but we don't really know that.It's not very good criterion.OK?The last thing is that chemical changes produce new substances.The new substances that are produced have very differentproperties from the original substances.For example, ordinary table salt, sodium chloride, is a whitecrystalline powder that's an essential nutrient for life processes.It's made out of sodium and chlorine.You already saw the reaction of sodium with water earlier in the program.

 

Sodium is a highly reactive, very poisonous metal.In fact, if you ate a piece of sodium, you'd be really uncomfortable really fast.Chlorine, on the other hand, is a green poisonous gas.So poisonous, in fact, that it was used as a military gas in WorldWar I and so potent that it was outlawed by the GenevaConvention as being cruel and inhumane warfare.Not that that stops you from using it, but it's a very powerful stuff.So, here on one hand you have this white silvery soft metal that's very reactive.On the other hand you have this green poisonous gas that's also very reactive.You combine them together the form this white crystallinesubstance, table salt, which has properties unlike either the sodium or the chlorine.So, this is one way to identify chemical changeif entirely new substances are produced.I can also give you an example of this one.Here I have, I want to get some of my chemicals here, and whatI have here is some sodium sulfide and some cadmium nitrate.

 

Let's go to the ELMO and I'll show you how these work.So, what I'm going to do is to pour these things into a beaker.I'm going to pour the cadmium nitrate into one beaker,and I'm going to pour the sodium sulfide into the other beaker.And you'll notice as I do this that these are both transparent liquids.In fact, you'd be hard pressed from lookingat either one of them to tell which one is which.One of them contains cadmium and nitrateand the other one contains sodium and sulfide.When I pour them together, this is neat, watch what happens here.Mix them together like this.Watch what happens.Notice that the reaction of the two of them forms thisbrilliant yellow powder which it's not actually dissolvedin the water, but it's sort of floating in the water.This is the cadmium yellow that artists use.If you're an artist, you've probably seen cadmium yellow oil paints.

 

The cadmium in certain solutions gives off this brilliant yellow color.So here we have a substance, yellow in color, very thick,very heavy, that's unlike either of the two solutions that it was formed from.It's not always easy to tell.What I mean by that is that although this is a goodcriterion, this, this change in composition, it's not alwayseasy to tell, especially if you don't already have a knowledge.For example, if you'd never seen ice melt to water before,how would you know that ice and water are the same substance?If you lived in a place where there was always only ice, you'd never know.So, in principle, it sounds like a good criterion, but in practice,it's not always that easy to follow.I should...meaning that it's not always easy to know whetheror not something is a new substance or whether it'ssimply a different state or different form of the same substance.OK.I said that was the last thing, but this,it was actually the next to the last thing.This is the last, last thing.And this is really the one that is most definitive for decidingwhether a reaction is a chemical or physical change.And that is that physical changes occur in variable ratios.What I mean by that is that you can dissolve various amountsof salt in a glass of water, or you can alloy variousamounts of metals with one of the other.You can form an alloy of copper and silver, for example, that's90% copper and 10% silver, or 50% of each or 40 and 60 of each, and so on.Water and alcohol can be mixed in any proportion, for example.In fact, you can dissolve an infinite amount of alcohol in water and vice versa.So, the physical mixtures allow for infinite variation in ratios.Chemical changes do not.Chemical compounds have set formulas.What that means is that when you react two chemicalswith one another, they'll always react with eachother in the same proportions by weight.

 

We'll take up this issue in a later lesson when we get into thestudy of chemical laws and so forth, but, for example,hydrogen and oxygen always combine with each otherin the ratio of 8 to one to form water.If you have extra hydrogen or extra oxygen, it simply doesn't react.It's simply left behind after the reaction takes place.So, chemical reactions take place in fixed ratios and leave behindthe excess material in an unreacted state.So, I mentioned before that energy is involvedin chemical changes and chemical reactions.But we need to specify that a little bit more.This is really a connection between the Newtonian part and the chemistry part.Because the concept of energy, remember, was shown by Jouleto be related not just to mechanical energy, but to thesevarious other forms of energy including chemical energy.And the fact that chemical reactions give off or absorbheat means that there must be some physical connectionbetween the concepts of chemistry and the concepts of physics.And heat really turns out to be the anchor or the linkage between these two things.So, basically there are two kinds of chemical reactions as far as heat goes.There are those that give off heat.Those are called exothermic reactions.Think of the word, exit.Exit means out of.So heat is given off or heat comes out of the chemical reaction.These are things like combustion, for example,which gives off a tremendous amount of heat.The other one I'll show you on the ELMO in a minuteis the dissolving of sodium hydroxide, or lye.

 

Now you're probably aware that combustion requiresa sort of a kick to get it started.This is often true of many chemical reactions.They require an activation energy before they become initiated.Like the magnesium that I burned earlier.It requires an initial input of energy, but once that inputof energy is there and it reaches a critical point, then the energytransfer or the energy, in this case, the energy given off, is spontaneous.The other kind of reaction is one in which energy isabsorbed, or which heat is absorbed.This is called an endothermic reaction.Think of "into."Endo, into, sort of linguistically sound the same.So, endothermic reactions absorb energy.There are not very many of these that are common, but one that'scommon, I'll show you on the ELMO is the dissolvingof ammonium chloride in water.This is using cold packs.You know for athletics.You can buy them at Longs.You have this little cold pack and you break it openand it gets cold; instant ice, they call it.So, let's go to the ELMO and I'll show you example of these twodifferent types of energy reactions.

 

 

 

The first one I want to do is to dissolve a little bit of sodiumhydroxide which I have a bottle here which is verycarefully labeled, sodium hydroxide.This is a fairly caustic substance.It's something that's used in Draino, among other things.It's very caustic.It tends to dissolve waxes and grease and that sort of thing.So what I want to do is to add water to this.I want to put the thermometer in here, and notice that thethermometer is starting out here somewhere about 18 or 19 degrees Celsius.And it's not so important to read the temperature all the time,what's important is simply to note that the temperature goesup when the stuff starts to dissolve.It shouldn't take very long before the temperature goes up.I might have to stir it a bit to get it to do that.But once it starts to dissolve, the temperature should go up very quickly.

 

I know it's hard to read the thermometer while I'm doingthis, and "Hey," you say, "the thermometer is going down first."What do you suppose causes that?That's a good thing to write about isn't it?Why does the thermometer go down first when I pour the water into it.Oh, let's see what happens here.Maybe while that's sitting there, warming up a little bit, I'll goahead and...oh, it's already moving.You see the thermometer going up?Look at it.It's up to 22.The stuff should get pretty hot.I'll tell you what I'm going to do.I'm going to cook this a little faster by addingsome more sodium hydroxide in there.Just to keep it going.By the way, if you're trying this stuff at home, be aware thatif you just mix Draino with water, it does get very hot.In fact, that's part of the cleansing action that take placein your drain, is that it heats up the drain.But, see the temperatures is going up?It's almost up to 30 degrees Celsius already.So, this is giving off quite a bit of heat.It's actually, the container is actually starting to get fairly warm.I think it's more a matter of the thermometerresponding slowly than it is the reaction.Look at it going, it's up to 35, getting all the way up to 40 degrees.So, I apologize for moving the thermometer around and I guessif I was being a good chemist, I'd be stirring this with a glass rod.I can feel the heat coming off of this, off of this now.It's up to, again, almost up to 60 degrees now.It's what, 55?So, you can see it's getting quite warm.So, I'm going to leave the thermometer in therefor a minute while I do the same thing with the ammonium chloride.I'm going to take some ammonium chloride powder here.Now this one takes a little longer to get started because theammonium chloride doesn't dissolve as well as the sodium hydroxide does.But if I put a good portion of it in here, this, notice,is very carefully labeled ammonium chloride,so we always know what we have in our bottles.

 

 

 

One of the things about chemicals is you always want to knowexactly what chemicals you're using and don't just startmixing chemicals on your own at home.I mean, you know, it looks like it's a lot of fun to do thisand everything, but in reality, the chemicals are, can be quitedangerous, if you don't know what you're doing and juststart mixing, even household chemicals.OK.So there's the ammonium chloride.I'm washing off the thermometer to get itback down to a cooler temperature.So, I'm going to add some water here to the ammonium chloride,and watch what happens to the thermometer.It's starting out again.I've got it down to about 20 degrees.Add a little bit of water there.And then I'll bring the big bottle out and pour some water in like that.Again, this is instant cold.Look at that.So already the temperature's dropped to 10 degrees Celsius.And I haven't even hardly started stirring it yet.And you can actually freeze water doing this.You may remember that when Fahrenheit made histemperature scale he used the mixture of ammonium chlorideand water because that was the coldest substance...I should say, ammonium chloride and water ice because that wasthe coldest substance he could make in the laboratory.So, look at that.It's almost down to freezing temperature of the wateralready, after only a couple of minutes.So on one hand you have an exothermic reaction,the sodium hydroxide, where it heats up.On the other hand we have the endothermic reaction whichactually becomes colder and if I feel this thing, it's actually quite cold.It's actually even starting to sweat a little bit.

 

Now it's time to approach that forbidden subject of chemistry.I say forbidden because a lot of times when you use a word likechemistry, people's immediate reaction is, "Oh, no, not chemistry."But chemistry isn't really that bad.I mean, we're going to study chemistry the same way we studied physics.We're going to be looking at the science of chemistry,and the development of the science of chemistry,much the way we did with physics.Not looking at specific reactions,not worrying about specificamounts of chemicals,but looking at it in a sort of a qualitative wayand in a social historical way.So, what exactly is chemistry?Chemistry is about the chemical properties of substances.We've spent some time in this program lookingat the chemical properties of substancesand we realize that there's a wide variety of properties.And this is one of the things that chemists study, is tryingto classify and figure out what substances there are,what their properties are, which things react with what,what sorts of products you get, and also, of course, is the ideaof making new chemicals, synthetic chemicals, which canhelp us industrially, personally or for medicines and so forth.Chemistry is also about elements and atoms.

 

 

The concept of elements and atoms which I mentionedearlier in this program, and which we'll come back to later on,is one of the central ones for all of modern science.So we're looking at not only elements and atoms in chemicalproperties of the substances, but the chemical propertiesof the chemical elements, themselves.And again, without knowing further what chemical elementsare, this may not register right away.But the difference between elements and substances will become clear to us.So we're looking at reactions between elements.We're looking at the elemental make up of various substances.What kinds of things are substances made out of?What's the human body made out?What's rocks made out of?What are trees made out of?So, that, along with the nature of chemical reactions.And I want to make it clear at this point that in the nextprogram we're going to be studying alchemy, and I wantto make it clear that there's a tremendous distinctionbetween the science of chemistry and the science of alchemy.It's a similar distinction between the scienceof astrology and the science of astronomy.Whereas, astrology is concerned with the affectof the movements of the planets on humans and their affairs,and astronomy is concerned simply with the nature of the heavenly objects.Alchemy is concerned with the spiritual, mysticalqualities of substances; whereas, chemistry isconcerned with the nature of the substances.

 

So, keep in mind that these two terms are very distinctand I think in the next program when we get to the conceptof alchemy, we'll see very clearly how this concept turnsinto the science of chemistry much the way that astrologyturned into the science of physics.In this program we've tried to show what matter is, how it'sclassified, an overview of how our views of it have changedand how chemical changes take place.We examined the distinction between physical and chemicalproperties and between physical and chemical change.We did this because most people don't see these kinds of changestake place, at least with laboratory chemicals,and we wanted to make sure that when we get into this nextsection that you've seen some of these things take place.So, after the chemical and physical properties and changeswe took a brief look at the role of heat in chemical reactions,and then a very brief sojourn through the scienceof chemistry which is, after all, the topic of our final sectionof our journey down this long river of scientific heritage.Well, you know, I think that's about it for this program.So, remember, when it comes to science, get physical.Silico: "I liked the chemical things.When we get home can I try some of that stuff.Why didn't you use "litus lay scree" for the liquid crystal part?Why didn't you talk about the chemistry of silicon?"Music