00:00:00 Hello, I am Harry Sello. It is my pleasure to introduce Tempest in a Test Tube, a television

00:00:13 show which made its debut August 24, 1955 on KQED Channel 9, the educational station

00:00:21 for the San Francisco Bay Area. Tempest was a series of 53 half-hour shows pioneering

00:00:29 a new approach in which I, as lecture demonstrator, gave live, unrehearsed presentations of a

00:00:37 series of chemical experiments. These were designed to illustrate basic, simple chemical

00:00:43 principles. The purpose was to stimulate an interest in chemistry by teenage students

00:00:50 and by adults. The talks and experiments had to be entertaining, educational, and simple.

00:00:59 Spontaneity and liveliness were key to the approach. All the experiments used in the

00:01:04 shows were designed and constructed by members of the California section of the American

00:01:09 Chemical Society. The participants were employed by the Shell Development Company, Emeryville,

00:01:16 and by Chevron Research, Richmond. A grant of $52,000 from the Ford Foundation and National

00:01:24 Educational Television permitted the filming of the first 24 shows of the series. The management

00:01:31 for the ACS consisted of Alan Nixon, section chair, Fred Stross, TV committee chair, myself

00:01:39 as first emcee, and Aubrey McClellan, second emcee. We four constitute the core of the

00:01:47 present committee. The series was extremely popular then with KQED viewers of all ages.

00:01:57 The senior chemist committee of the California section today is determined to revive Tempest

00:02:04 for the benefit of elementary schools, high schools, adult education classes, ACS local

00:02:11 collections, historical archives, TV stations, and similar organizations. We believe in chemistry

00:02:19 as a second language. While basic principles have not changed, practices have. Forty-five

00:02:28 years ago, such simple chemical demonstrations were not treated with the degree of safety

00:02:34 considerations that they are today. Today, even such simple demonstrations would be carried

00:02:41 out with the proper regard for safety glasses, shields, protective gloves, laboratory coats,

00:02:49 and visible fire extinguishers. The principle of safety first would be explicitly present

00:02:56 as part and parcel of a modern Tempest in a Test Tube.

00:03:41 Tempest in a Test Tube, a series of experiments designed to explain the mysteries of chemistry

00:03:56 and the laws that govern it. Produced by KQED San Francisco, in cooperation with the California

00:04:11 section of the American Chemical Society, for the Educational Television and Radio Center.

00:04:24 And now let's go to our laboratory and meet Dr. Harry Sello.

00:04:29 So, most of the reactions that a chemist will study are very similar to the one I'm

00:04:36 about to do. Pour a little bit of one chemical, and then let's stir in the next one. This

00:04:56 is a very common type of reaction. The reaction occurs immediately as soon as the chemicals

00:05:04 are mixed. There are many such reactions that the chemist studies. This particular one was

00:05:09 the reaction between silver nitrate and hydrochloric acid. The product, the white solid, is silver

00:05:16 chloride. Of course, the nitric acid that's formed stays in solution. But the reaction

00:05:21 occurs immediately. In this talk, we will concern ourselves with another kind of chemical

00:05:28 reaction, one which is not so common, the delayed chemical reaction, or what we sometimes

00:05:34 fondly call chemical clock reactions. Let's look at an example of a delayed chemical reaction.

00:05:42 Here's a little bit of one reagent. Now, add next. Well, nothing yet. There it goes.

00:06:06 Now the white precipitate forms. Notice that the reaction did not occur immediately

00:06:12 upon mixing the two solutions. At least nothing that we could see occurred immediately. There

00:06:18 was some delay. These two reagents are sodium thiosulfate, our old friend, hypo, and hydrochloric

00:06:28 acid. The two react together. Sulfur is one of the products of the reaction, but the sulfur

00:06:35 is not formed immediately. It is formed only after some preceding reactions occur. What

00:06:43 I mean is this, simply. This is a complicated situation. It's not just a simple reaction.

00:06:49 There's not just one. There are several. The main visible reaction is preceded by one or

00:06:56 two others, so that not until the first ones are out of the way does the main reaction

00:07:01 occur. In this case, sulfur is formed early, but you can't see it. It's just too small

00:07:08 a particle to be visible. The sulfur particles grow, become bigger grains until they become

00:07:13 visible and white, and now as they get bigger and bigger, really heavy in concentration,

00:07:20 they even have a yellow cast to them, and this particular one smells strongly of sulfur.

00:07:28 But however, there is a delay in the main reaction. This, then, is the first example

00:07:34 of what we'll call in this talk chemical clock reactions. Now when the chemist runs across

00:07:42 a situation like this, he proceeds to study what factors, just what things, will influence

00:07:49 the delay of a chemical reaction. Will it always occur? Are there other reactions like

00:07:53 this? How can I adjust this delay so we can study it at various intervals? Let's go on

00:08:01 and look at just such a situation of examining the factors which affect a chemical reaction.

00:08:11 Let me pour a little bit of this solution into the beaker. Water clear solution. Here

00:08:23 is a beaker, the same size, rather, that's been standing on ice for a while. It's chilled.

00:08:30 And here is some more of the same solution, which has been standing here for a few minutes,

00:08:35 also being chilled. I'll pour that in here. Now, let's see, put them like this, there.

00:08:59 Get them a little closer together so I can pour these both at the same time. The same

00:09:07 reagent, I'll pour these in simultaneously. Vigorous reaction. But look at the second

00:09:22 one. Phew! There's been some reaction. It's black, but notice the difference. Two things

00:09:34 that are different. One, it was delayed in starting, this was black while this was clear,

00:09:38 and then turned black, but not nearly as vigorous as the first one. Well, the reagents were,

00:09:45 in both cases, the sugar solution, a concentrated solution of sugar, cane sugar actually, sucrose,

00:09:52 plus concentrated sulfuric acid. One of the products formed is carbon. Also some gaseous

00:10:00 fumes, which seem to be affecting the lecture for some reason. Very pungent. Carbon is formed

00:10:07 in both cases. However, because of the low temperature, this chilled reaction was slower.

00:10:14 It took a longer time to get started. So now we must write our first factor, which we found

00:10:19 affects chemical reactions. Here is the table we'll start. We'll edit factors which influence

00:10:26 rate. By rate, I mean rate of chemical reaction, that is the speed with which things occur,

00:10:32 with which the visible result occurs. This first factor then is the temperature. In this case,

00:10:45 the result was the obvious one. The lower temperature caused the rate of reaction to

00:10:50 be slower. Lowering the temperature decreases the rate. Let's put it down that way. Lower

00:10:58 T decreases rate. You can look at that in the following way. Chemical reaction depends upon

00:11:16 various molecules getting together to react. The temperature of the solution is a measure

00:11:24 of how fast the molecules are moving around. That is, the higher the temperature, the faster

00:11:28 they're moving around. The more often they will bump into each other. If this rate of

00:11:33 bumping can be slowed down, naturally the rate with which the reaction occurs will be

00:11:38 slowed down. This is exactly what happened. Sulfuric acid needs to come in contact with

00:11:43 the cane sugar, with the sucrose. If you slow down the rate with which these come together,

00:11:48 at the same time decrease the number of collisions which occur, then you slow down the rate.

00:11:53 This is exactly what happened. Now, in the next series of experiments, we'll have a quantitative

00:12:01 way of estimating this. Let's actually time this delay in reaction that we've been talking

00:12:07 about. Let's use a timer to measure more accurately the amount of delay in the chemical reaction.

00:12:14 Mix these two solutions, stir, and start the timer.

00:12:28 Fifteen seconds have gone by. There it goes. Just about 20 seconds. Let's reset this to

00:12:56 zero. So at room temperature, these two reagents take about 20 seconds to react. Let's just

00:13:13 write this number down and keep it here for reference. Off on the side here, 20 seconds

00:13:18 is the base time for room temperature reactions. Now all we have to do is compare several others

00:13:27 to something like this to tell whether we have a factor which makes the reaction go

00:13:33 slower or faster. Here are the same solutions as the previous, except that in two of these,

00:13:41 I've started them off with some water, just plain distilled water, different amounts.

00:13:46 That is, in the first pair, we have exactly the same situation, or that is very close

00:13:51 to it. The next pair have the same reagents, but here is 50 milliliters of water added

00:13:58 to begin with, and in this one, 100 milliliters of water added to begin with. So that here

00:14:04 we'll have a concentrated case, let's say, here a more dilute case, and here even a more

00:14:10 dilute example. Let's time each one in turn and see what happens. Here's the first, which

00:14:16 should be roughly the same as the previous one if everything works right. These never

00:14:21 come out exactly because the volumes aren't exactly the same. Let's mix these two and

00:14:28 quickly start the timer again. About 18 seconds for the first one. Well, that's fairly close.

00:14:53 We had 20 here. For the same one, the second try, 18 seconds. Actually, there were different

00:14:59 volumes used in this particular one than that one. Equal volumes, here 100 milliliters each,

00:15:04 here 50 milliliters each, so the time wasn't too far off. Now let's then do the one with

00:15:11 the first bit of water added for dilution. Start the timer at zero again. Make sure things

00:15:30 are mixed here separately first. Now, see if you can guess whether this should be longer

00:15:47 or shorter. There's coming up the 18 seconds of the first one already. We're past that

00:16:01 point. There it goes, 33 seconds. 33 seconds for the 50 milliliters of water. This is,

00:16:25 we had a column here, water, H2O, zero. We got 18 seconds for 50 of water. We get 33 seconds.

00:16:35 Zero, 50, 18, and 33. Okay, now the next one. Reset the timer. Just have to take time to do

00:16:49 this. So, there's a, you can tell a little trace of reaction starting before the main reaction

00:17:01 occurs. That's because the indicator which is being used is not completely soluble in the

00:17:06 solution. There are little particles of it floating around. So you get a sort of a little

00:17:13 tiny bit of advance warning, but the main reaction occurs quite quickly. Now here's the one with the

00:17:17 100 milliliters of water. Mix that. Start the timer. Of course, you can already guess that

00:17:29 we'll have to do a little bit of waiting on this one. Patience is a virtue which every chemist

00:17:35 should have. 20 seconds. Get this out of the way and get it over here to where I can see this

00:17:53 thing. There. 35 seconds. We're past the second one already. 40. Not a trace of reaction yet.

00:18:10 There it goes. Just about 50 seconds. So with 100 milliliters of water added to both chemicals,

00:18:23 we had 50 seconds for reaction. Now, the principle illustrated here is that when the reactants,

00:18:33 or reagents, are diluted, spread apart, the reaction is slower. This fits from the molecular

00:18:41 notion because the molecules then have to travel longer distances to shoulder their

00:18:46 way through intervening water molecules in order to react. So we must now write down

00:18:51 our second factor for those which affect the rate or influence the rate, and that is concentration.

00:18:57 Lower the concentration decreases rate. By concentration, I don't mean the concentration

00:19:19 that the audience gives, nor that of the lecturer. I mean the concentration of the molecules in the

00:19:25 solutions. Let's go on then and look at the next factor. Need a timer again. We'll start it at zero

00:19:34 once more. Now, we already had an advanced look at this particular factor, temperature, when we

00:19:43 looked at the sulfuric acid and the sugar. But here is the same reaction that we've just studied,

00:19:49 only temperature now is the factor, more quantitative than the sugar reaction was.

00:19:53 Here's the first one. These jars now have been standing on the hot plate for some time. They're

00:20:00 quite warm. They're so warm that the labels are just about falling off. Stick on labels. Now,

00:20:09 I must be sure that we put the indicator in this one just before starting so we can tell

00:20:15 when the reaction occurs. I'll explain about this indicator in just a moment. Here's the one. Stir

00:20:26 it up well. Now, I have to try to operate quickly on this one. Get over here to hit this as soon

00:20:35 as we mix the two together. They're quite warm. Mix, start. Well, that maybe took one second.

00:20:43 Actually, the reaction practically went as soon as we mixed. So, let's continue our column here.

00:20:51 One second or less. Let's say zero to one second for hot. Kind of getting off the edge of the board

00:21:03 here. Zero to one second for hot reaction mixtures. Here is the comparison, the standard so-called at

00:21:12 room temperature. We have to be sure that we do that one so we can have something to refer to.

00:21:16 Let's see. Come around from this side. It works better. There we go. Again, indicator. What I was

00:21:26 going to say about the indicator is this is a reaction involving a base, hydroxyl ion. This

00:21:33 indicator is thymolphthalein, a jawbreaker, thymolphthalein. It turns dark in the presence

00:21:40 of base. The reaction completion is signified when the base is formed so the thymolphthalein

00:21:45 turns dark. Here is the reaction at room temperature by way of comparison. We already

00:21:51 have done this twice. Let's just repeat it for comparison. Oh, you have to have about three

00:21:57 arms to do this, maybe even two heads. We should come close to the time we observed before,

00:22:08 the 20 or the 18 seconds. It says here. There we go, 20 seconds. Very good, even if I say so

00:22:21 myself. Room temperature, 820 seconds. That was what we observed in the first case. Now,

00:22:32 the final bit is the one using the lower than room temperature, the chilled solutions. Get

00:22:43 these out here where we can see them. Indicator. Mix these. Good mixing is always a factor.

00:23:07 Now mix the two together, start the reaction, and let's observe this last time for this

00:23:16 reaction. This is now lower than room temperature. There is 20 seconds coming up. Now 20 seconds,

00:23:31 so we're already past the time for the room temperature reaction. 35, 50,

00:24:01 coming up. Any time now, we're ready for it. 65, coming up. A little trace of reaction appearing

00:24:17 at the top around where the indicator is concentrated. 70. Let's go, there we go. 75

00:24:29 seconds, or about 77 seconds. Well, this clearly illustrates then that cooling slows down the

00:24:34 reaction. Let's just write this last number down. 77 seconds at lower than room, less than room

00:24:42 temperature. The sign means less than. Well, so we've illustrated then with respect to this

00:24:51 quantitative nature that is accurately shown, as good as we could with the timer, that these

00:24:57 factors truly affect chemical reactions. We've shown temperature and concentration. In the next

00:25:03 experiment, there will be shown a slightly different factor which affects chemical reactions,

00:25:10 but also a different chemical reaction. We have shown two materials which reacted together in a

00:25:16 solution, that is, everything was mixed throughout. By the way, these two materials were, on the one

00:25:21 case, formaldehyde solution, on the other case, a mixture of sodium sulfite, sodium bisulfite.

00:25:27 That pair reacted with formaldehyde in this delayed manner, and the indicator,

00:25:32 thymophthalein, showed the change. Here is a setup where we're using an induction coil to

00:25:39 throw a spark. Now, I have here placed between the electrodes a piece of aluminum. I'll place

00:25:47 it right in there again, right between the two electrodes. If I make contact,

00:25:51 I can cause a spark to flow across the electrodes and right through the aluminum.

00:26:02 There has been no visible effect on the aluminum. Nothing has happened. The spark just flowed right

00:26:15 through. It's a conductor, so it's not surprising that this happened. But let's do this reaction

00:26:21 with aluminum in a slightly different form. Here's my aluminum in a slightly different form,

00:26:25 in the form of a powder. I'll put this powder in this flask. A goodly amount in there,

00:26:37 even a little bit more will do. Lower the electrodes down into the powder,

00:26:44 or close to it, and put in a device for blowing a little jet of air.

00:26:52 See if I can just get this placed right here. So this will go right down into the powdered aluminum.

00:27:02 Come on, behave. I'll just turn this around. We want to make sure that the little air blower

00:27:14 goes right down into the middle of the powder, right near the spot. There we go. Now,

00:27:19 better put my safety glasses on for this one, and for Mars. I'll throw the spark,

00:27:31 cause the spark to go. There it is, right down in the flask, and then watch what happens when

00:27:36 I start squeezing the bulb. A rather rapid reaction. That was also aluminum. The aluminum

00:27:48 reacted in its powdered form somewhat quicker than it reacted, if at all, in the solid form.

00:27:56 The only difference in these two experiments was the fact that in the one case we used solid

00:28:02 aluminum, and the other powdered aluminum. So the only difference was the state of subdivision. How

00:28:07 small the particles of aluminum were. Here, the oxygen of the air can only get at the aluminum

00:28:13 on two surfaces. Maybe a little bit along the edge, that's tiny. In the case of the powder,

00:28:19 all the tiny little particles of aluminum can be surrounded by oxygen. So that when the spark is

00:28:24 thrown, the reaction starts, aluminum reacts with oxygen, and you get a very vigorous flash.

00:28:29 Aluminum oxide is formed. So we must then write a third factor which affects chemical reactions.

00:28:35 Call it the state of subdivision. Subdivision. I don't mean any particular real estate or anything

00:28:57 like that, but the fine particles react more quickly. So let's say fine particles faster.

00:29:10 Well, let's summarize all this mumbo-jumbo. What have we seen in this talk? We examined

00:29:22 the factors which influence the rate of a reaction. The reason we could talk about this

00:29:27 is that there are two kinds of reactions, roughly, in this sense. Reactions which occur so fast that

00:29:34 there is no delay. Instantaneous reactions. That was illustrated by the reaction between

00:29:39 silver nitrate and hydrochloric acid. We then showed an example of a reaction which occurred

00:29:49 with a delay. The reaction between sodium thiosulfate and hydrochloric acid. In this case,

00:29:55 sulfur particles were formed, sulfur dioxide was given off, and you could smell the sulfur

00:30:01 dioxide. A smell which a lot of people associate with sulfur. Actually, the sulfur doesn't have

00:30:08 an odor of its own, but the sulfur dioxide which is present usually gives the pungency. Well,

00:30:13 we went on then to show that temperature affects reactions. That was the first factor. The lower

00:30:19 the temperature, the lower the rate. The slower the reaction proceeded. This was illustrated very

00:30:24 graphically by the timed reactions in which when we chilled the reactants, that is started out with

00:30:36 room temperature and less than room temperature, we found that the reaction took longer and longer

00:30:42 to proceed. This was easy to explain in terms of molecules reacting in that the lower the

00:30:50 temperature, the slower the molecules moved around. The less often they collided so that

00:30:54 the less often they could react. Conversely, if we increased the temperature, we would increase

00:31:00 the rate. Then we could see by adding some water, different amounts that we could also lower the

00:31:07 rate. That is, diluting the reaction decreased the rate. So the lower the concentration, the

00:31:14 lower the rate. Also explainable in terms of the molecules in that the fewer of them there are,

00:31:20 the less will be the amount of reaction or the slower will be the reaction. Not the less will

00:31:25 be the amount of reaction. That's not quite right. The slower will be the reaction. Finally,

00:31:29 by choosing a dust explosion type of reaction, we showed that aluminum in a finely divided state

00:31:34 would really react explosively, whereas ordinary aluminum does not react with oxygen very quickly.

00:31:40 In fact, this dust explosion is typical of what you might see in the papers from time to time,

00:31:45 dust explosions in grain elevators, coal mines, and so forth. Chemical clock reactions. Thank you.

00:32:34 This is national educational television.