Chapter Ten

CHEMICAL CHANGE AND ENERGY

SECTION 46. What things are made of: Elements.

What is water made of?

What is iron made of?

Is everything made out of dust?

One of the most natural questions in the world is, "What is this made of?" If we are talking about a piece of bread, the answer is, of course, "flour, water, milk, shortening, sugar, salt, and yeast." But what is each of these made of? Flour is made of wheat, and the wheat is made of materials that the plant gets from the earth, water, and air. Then what are the earth, water, and air made of? A chemist is a person who can answer these questions and who can tell what almost everything is made of. And a strange thing that chemists have found out is this: Everything in the world is made out of one or more of about eighty-five simple substances called elements.

WHAT AN ELEMENT IS. An element is a substance that is not made of anything else but itself. Gold is one of the eighty-five elements; there are no other substances known to man that you can put together to make gold. It is made of gold and that is all. There is a theory that maybe all the elements are made of electrons in different arrangements, or of electrons and one other thing; but we do not know that, it is only a theory. Carbon is another element; pure charcoal is carbon. The part of the air that we use when we breathe or when we burn things is called oxygen. Oxygen is an element; it is not made of anything but itself. There is another gas which is often used to fill balloons that are to go very high; it is the lightest in the world and is called hydrogen. Hydrogen is an element.

For a long time people thought that water was an element. Water certainly looks and seems as if it were made only of itself. Yet during the thousands of years that people believed water was an element, they were daily putting two elements together and making water out of them. When you put a kettle, or anything cold, over a fire, tiny drops of water always form on it. These are not drops of water that were dissolved in the air, and that condense on the sides of the cold kettle; if they were, they would gather on the kettle better in the open air than over the hot fire. Really there is some of that very light gas, hydrogen, in the wood or coal or gas that you use, and this hydrogen joins the oxygen in the air to make water whenever we burn ordinary fuel.

But the best way to prove that water is made of two gases is to take the water apart and get the gases from it. Here are the directions for doing this:

EXPERIMENT 90. A regular bought electrolysis apparatus may be used, or you can make a simple one as follows:

Use a tumbler and two test tubes. If the test tubes are rather small (3/8'' X 3'') they will fill more quickly. Dissolve a little lye (about 1/8 teaspoonful) in half a pint of water to make the water conduct electricity easily, or you may use sulfuric acid in place of lye. Pour half of this solution into the tumbler. Pour as much more as possible into the test tubes, filling both tubes brim full. Cover the mouth of each test tube with a small square of dry paper or cardboard, and turn it upside down, lowering it into the tumbler.

The "electrodes" are two 3/4'' pieces of platinum wire (#30), which are soldered to two pieces of insulated copper wire, each about 2 feet long. The other ends of the copper wire are bare. Fasten the bare end of one copper wire to one nail of the nail plug if you have direct current (d. c.) in the laboratory, and fasten the bare end of the other wire to the other nail; then turn on the electricity. If you do not have direct current in the laboratory, attach the copper wires to the two poles of a battery instead.

Bend the platinum electrodes up so that they will stick up into the test tubes from below. Bubbles should immediately begin to gather on the platinum wire and to rise in the test tubes. As the test tubes fill with gas, the water is forced out; so you can tell how much gas has collected at any time by seeing how much water is left in each tube.

One tube should fill with gas twice as fast as the other. The gas in this tube is hydrogen; there is twice as much hydrogen as there is oxygen in water. The tube that fills more slowly contains oxygen.

When the faster-filling tube is full of hydrogen--that is, when all of the water has been forced out of it--take the electrode out and let it hang loose in the glass. Put a piece of cardboard about 1 inch square over the mouth of the test tube; take the test tube out of the water and turn it right side up, keeping it covered with the cardboard. Light a match, remove the cardboard cover, and hold the match over the open test tube. Does the hydrogen in it burn?

When the tube containing the oxygen is full, take it out, covered, just as you did the hydrogen test tube. But in this case make the end of a stick of charcoal glow, remove the cardboard from the tube, and then plunge the glowing charcoal into the test tube full of oxygen.

Only oxygen will make charcoal burst into flame like this.

When people found that they could take water apart in this way and turn it into hydrogen and oxygen, and when they found that whenever they combined hydrogen with oxygen they got water, they knew, of course, that water was not an element. Maybe some day they will find that some of the eighty-five or so substances that we now consider elements can really be divided into two or more elements; but so far the elements we know show no signs of being made of anything except themselves.

The last section of this book will explain something about the way the chemist goes to work to find out what elements are hidden in compounds.

THE QUICK WAY CHEMISTS WRITE ABOUT ELEMENTS. Since everything in the world is made of a combination or a mixture of elements, chemists have found it very convenient to make abbreviations for the names of the elements so that they can quickly write what a thing is made of. They indicate hydrogen by the letter H. O always means oxygen to the chemist; C means carbon; and Cl means chlorine, the poison gas so much used in the World War. The abbreviation stands for the Latin name of the element instead of for the English name, but they are often almost alike. The Latin name for the metal sodium, however, is natrum, and chemists always write Na when they mean sodium; this is fortunate, because S already stands for the element sulfur. Fe means iron (Latin, ferrum). But I stands for the element iodine. (The iodine you use when you get scratched is the element iodine dissolved in alcohol.) It is not necessary for you to remember the chemical symbols unless you mean to become a chemist or unless you read a good deal about chemistry. But almost every one knows at least that H means hydrogen, O means oxygen, and C means carbon.

When a chemist wants to show that water is made of hydrogen two parts and oxygen one part, he writes it very quickly like this: H2O (pronounced "H two O"). "H2O" means to a chemist just as much as "w-a-t-e-r" means to you; and it means even more, because it tells that water is made of two parts hydrogen and one part oxygen. If a chemist wanted to write, "You can take water apart and it will give you two parts of hydrogen and also one part of oxygen," this is what he would put down:

H_2O -> 2H+O.

If he wanted to show that you could combine two parts of hydrogen and one part of oxygen to form water, he would write it quickly like this:

2H+O -> H_2O.

These are called chemical equations. You do not need to remember them; they are put here merely so that you will know what they look like. Some of them are much longer and more complicated, like this:

HC2H3O2+NaHCO3 -> H2O+CO2+NaC2H3O_2.

This is the chemist's way of saying, "Vinegar is made of one part of hydrogen gas that will come off easily and that gives it its sour taste, two parts of carbon, three parts of hydrogen that does not come off so easily, and two parts of oxygen. When you put this with baking soda, which is made of one part of the metal sodium, one part of hydrogen, one part of carbon, and three parts of oxygen, you get water and carbon dioxid gas and a kind of salt called sodium acetate." Or, more briefly, "If you put baking soda with vinegar, you get water, a gas called carbon dioxid, and a salt." You can see how much shorter the chemist's way of writing it is.

SOME ELEMENTS YOU ALREADY KNOW. Here is a list of some elements that you are already pretty well acquainted with. The abbreviation is put after the name for each. This list is only for reference and need not be learned.

Aluminum (Al) Carbon (C) Charcoal, diamonds, graphite (the lead in a pencil is graphite), hard coal, and soot are all made of carbon. Chlorine (Cl) A poison gas that was used in the war. Copper (Cu) Gold (Au) Hydrogen (H) The lightest gas in the world; you got it from water in the last experiment and will get it from an acid in the next. Iodine (I) It is a solid; what you use is iodine dissolved in alcohol. Iron (Fe) Lead (Pb) Mercury (Hg) This is another name for quicksilver. Nickel (Ni) Nitrogen (N) About four fifths of the air is pure nitrogen. Oxygen (O) This is the part of the air we use in breathing. You got some out of water, and you will have it to deal with in another experiment. Phosphorus (P) Phosphorus makes matches glow in the dark, and it makes them strike easily. Platinum (Pt) Radium (Ra) Silver (Ag) Sodium (Na) You are not acquainted with sodium by itself, but when it is combined with the poison gas, chlorine, it makes ordinary table salt. Sulfur (S) Tin (Sn) Zinc (Zn)

For the rest of the elements you can refer to any textbook on chemistry.

HOW ELEMENTS HIDE IN COMPOUNDS. One strange thing about an element is that it can hide so completely, by combining with another element, that you would never know it was present unless you took the combination apart. Take the black element carbon, for instance. Sugar is made entirely of carbon and water. You can tell this by making sugar very hot. When it is hot enough, it turns black; the water part is driven off and the carbon is left behind. Yet to look at dry, white sugar, or to taste its sweetness, one would never suspect that it was made of pure black, tasteless carbon and colorless, tasteless water. Mixing carbon and water would never give you sugar. But combining them in the right proportions into a chemical compound does produce sugar.

Not only is carbon concealed in sugar, but it is present in all plant and animal matter. That is why burning almost any kind of food makes it black. You drive off most of the other elements and separate the food into its parts by getting it too hot; the water evaporates and so does the nitrogen; what is left is mainly black carbon.

MAKING HYDROGEN COME OUT OF HIDING. The light gas, hydrogen, conceals itself as perfectly as carbon does by combining with other elements. It is hiding in everything that is sour and in many things that are not sour. And you can get it out of sour things with metals. In some cases it is harder to separate than in others; and some metals separate it better than others do. But one sour compound that you can easily get the hydrogen out of is hydrochloric acid (HCl), which is hydrogen combined with the poison gas, chlorine. One of the best metals to get the hydrogen out with is zinc. Here are the directions for doing it and incidentally for making a toy balloon:

EXPERIMENT 91. Do this experiment on the side of the laboratory farthest from any flames or fire. Do not let any flame come near the flask in which you are making hydrogen.

In the bottom of a flask put two or three wads of zinc shavings, each about the size of your thumb. Fit a one-hole rubber stopper to the flask. Take the stopper out and put a piece of glass tubing about 5 inches long through the hole of the stopper, letting half an inch or so stick down into the flask when the stopper is in place (Fig. 162). With a rubber band fasten the mouth of a rubber balloon over the end of the glass tube that will be uppermost. Fill the balloon by blowing through the glass tube to see if all connections are tight, and to see how far it may be expanded without danger of breaking. You can tell when the balloon has about all it will hold, by pressing gently with your fingers. If the rubber feels tight, do not blow any more. Let the air out of the balloon again.

Now get some hydrochloric acid (HCl) diluted with three parts of water. Find the bottle marked "HCl, dilute 1-3," in which the acid is already diluted. Before you open the bottle, get some solution of soda, and keep it near you; if in this experiment or any other you spatter acid on your hands or face or clothes, wash it off immediately with soda solution. Remember this. Ammonia will do as well as the soda solution to wash off the acid, but be careful not to get it into your eyes.

Pour the hydrochloric acid (HCl) on the zinc shavings in the bottom of the flask, until the acid stands about an inch deep. Then quickly put the rubber stopper with its attachments into the flask, so that the gas that bubbles up will blow up the balloon.

If the bubbles do not form rapidly, ask the teacher to pour a little strong hydrochloric acid into the flask; but this will probably not be necessary. Let the balloon keep filling until it is as large as you blew it. But if the bubbles stop coming before it gets as large as that, close the neck of the balloon by pinching it tightly, and take the stopper out. Let some one add more zinc shavings and more acid to the flask; put the stopper back in, and stop pinching the neck of the balloon. In this and all other experiments when you use strong acids, pour the used acids into the crockery jar that is provided for such wastes. Do not pour them into the sink, as acids ruin sink drainpipes.

When the balloon is full, close the neck by slipping the rubber band up from the part of the neck that is over the glass tube on to the upper part of the neck. Pull the balloon off the glass tube and pinch the neck firmly shut. Take the stopper out and rinse the flask several times with running water. Any zinc that is left should be rinsed thoroughly, dried, and set aside so that it may be used again. Now tie one end of a long thread firmly around the mouth of the balloon and let the balloon go. Does it rise? If it does not, the reason is that you did not get it full enough. In that case make more hydrogen and fill it fuller, as explained above.

Here is another experiment with hydrogen:

EXPERIMENT 92. Put a wad of zinc shavings, about the size of the end of your little finger, into the bottom of a test tube. Cover it with hydrochloric acid (HCl) diluted one to three, as in the preceding experiment. After the bubbles have been rising for a couple of minutes, take the test tube to the side of the laboratory where the burners are, and hold a lighted match at its mouth. Will hydrogen burn?

Remember that the hydrogen which the zinc is driving out of the acid is exactly the same as the hydrogen you drove out of water with an electric current. There is a metal called sodium (Na) and another called potassium (K) which are as soft as stiff putty and as shiny as silver; if you put a tiny piece of sodium (Na) or potassium (K) on water, it will drive the hydrogen out of the water just as zinc drove it out of the acid. The action is so swift and violent and releases so much heat that the hydrogen which is set free catches fire. This makes it look as if the metal were burning as it sputters around on top of the water. There is so much sputtering that the experiment is dangerous; people have been blinded by the hot alkaline water spattering into their eyes. So you cannot try this until sometime when you take a regular course in chemistry.

GETTING OXYGEN, A GAS, FROM TWO SOLIDS. Oxygen (O) can hide just as successfully as hydrogen. Practically all elements can do the same by combining with others. Here is an experiment in which you can get the gas, oxygen, out of a couple of solids. If you went to the moon or some other place where there is no air, you could carry oxygen very conveniently locked up in these solid substances. Oxygen, you remember, is the part of the air that keeps us alive when we breathe it.

EXPERIMENT 93. In a test tube mix about one half teaspoonful each of white potassium chlorate crystals and black grains of manganese dioxid. Put a piece of glass tubing through a cork so that the tubing will stick down a little way into the test tube. Do not put the glass tubing through the cork while the cork is in the test tube: insert the glass tubing first, then put the cork into the test tube. Put one end of a 2-foot piece of rubber tubing over the glass tube and put the other end into a pan of water.

Fill a flask or bottle to the brim with water, letting it overflow a little; hold a piece of cardboard firmly over the mouth of the bottle; turn the bottle upside down quickly, putting the mouth of it under water in the pan; take the cardboard away. The water should all stay in the bottle.

Now shove the rubber tube into the neck of the bottle until it sticks up an inch or two. During this experiment, be careful not to let the neck of the bottle or flask pinch the rubber tubing; small pieces of wood or glass tubing laid beside the rubber tubing where it goes under the run of the neck will prevent this.

Hold, the test tube, tightly corked, over the flame of a burner, keeping the tube at a slant and moving it slightly back and forth so that all the material in it will be thoroughly heated. If you stop heating the test tube even for a couple of seconds, take the cork out; if you do not remove the cork, the cooling gas in the test tube will shrink and allow the water from the pan to be forced through the rubber tube into the test tube, breaking it into pieces.

When enough gas has bubbled up into the bottle to force all the water out, and when bubbles begin to come up outside the bottle, uncork the test tube and lay it aside where it will not burn anything; then slide the cardboard under the mouth of the bottle and turn it right side up; leave the cardboard on the bottle.

Light a piece of charcoal, or let a splinter of wood burn a few minutes and then blow it out so that a glowing coal will be left on the end of it. Lift the cardboard off the bottle and plunge the glowing stick into it for a couple of seconds. Cover the bottle after taking out the stick, and repeat, using a lighted match or a burning piece of wood instead of the glowing stick. If you dip a piece of iron picture wire in sulfur and light it, and then plunge it into the bottle, you will see iron burn.

Both manganese dioxid and potassium chlorate have a great deal of oxygen bound up in them. When they join together, as they do when you heat them, they cannot hold so much oxygen, and it escapes as a gas. In the experiment, the escaping oxygen passed through the tube, filled the bottle, and forced the water out.

WHAT BURNING IS. When anything burns, it is simply joining oxygen. When a thing burns in air, it cannot join the oxygen of the air very fast, for every quart of oxygen in the air is diluted with a gallon of a gas called nitrogen. Nitrogen will not burn and it will not help anything else to burn. But when you have pure oxygen, as in the bottle, the particles of wood or charcoal or picture wire can join it easily; so there is a very bright blaze.

Although free oxygen helps things to burn so brilliantly, a match applied to the solids from which you got it would go out. And while hydrogen burns very easily, you cannot burn water although it is two-thirds hydrogen. Water is H_2O, you remember.

WHAT COMPOUNDS ARE. When elements are combined with other elements, the new substances that are formed are called compounds. Water (H_2O) is a compound, because it is made of hydrogen and oxygen combined.

When elements unite to form compounds, they lose their original qualities. The oxygen in water will not let things burn in it; the hydrogen in water will not burn. Salt (NaCl) is a compound. It is made of the soft metal sodium (Na), which when placed on water sputters and drives hydrogen out of the water, and the poison gas chlorine (Cl), combined with each other. And salt is neither dangerous to put in water like sodium, nor is it a greenish poison gas like chlorine.

MIXTURES. But sometimes elements can be mixed without their combining to form compounds, in such a way that they keep most of their original properties. Air is a mixture. It is made of oxygen (O) and nitrogen (N). If they were combined, instead of mixed, they might form laughing gas,--the gas dentists use in putting people to sleep when they pull teeth. So it is well for us that air is only a mixture of oxygen and nitrogen, and not a compound.

You found that things burned brilliantly in oxygen. Well, things burn in air too, because a fifth of the air is oxygen and the oxygen of the air has all its original properties left. Things do not burn as brightly in air as they do in pure oxygen for the same reason that a teaspoonful of sugar mixed with 4 teaspoonfuls of boiled rice does not taste as sweet as pure sugar. The sugar itself is as sweet, but it is not as concentrated. Likewise the oxygen in the air is as able to help things burn as pure oxygen is; but it is diluted with four times its own volume of nitrogen.

A solution is a mixture, too; for although substances disappear when they dissolve, they keep their own properties. Sugar is sweet whether it is dissolved or not. Salt dissolved in water makes brine; but the water will act in the way that it did before. It will still help to make iron rust; and salt will be salty, whether or not it is dissolved in water. That is why solutions are only mixtures and are not chemical compounds.

EVERYTHING IN THE WORLD IS MADE OF ATOMS. Everything in the world is either an element or a compound or a mixture. Most plant and animal matter is made of very complicated compounds, or mixtures of compounds. All pure metals are elements; but metals, when they are melted, can be dissolved in each other to form alloys, which really are mixtures. Most of the so-called gold and silver and nickel articles are really made of alloys; that is, the gold, silver, or nickel has some other elements dissolved in it to make it harder, or to impart some other quality. Bronze and brass are always alloys; steel is generally an alloy made chiefly of iron but with other elements such as tungsten, of which electric lamp filaments are made, dissolved in it to make it harder. An alloy is a special kind of solution not quite like an ordinary solution.

You remember that in the opening chapters we often spoke of molecules, the tiny particles of matter that are always moving rapidly back and forth. Well, if you were to examine a molecule of water with the microscope which we imagined could show us molecules, you would find that the molecule of water was made of three still smaller particles, called atoms. Two of these would be atoms of hydrogen and would probably be especially small; the third would be larger and would be an oxygen atom.

In the same way if you looked at a molecule of salt under this imaginary microscope, you would probably find it made of two atoms, one of sodium (Na) and one of chlorine (Cl), held fast together in some way which we do not entirely understand.

The smallest particle of an element is called an atom.

The smallest particle of a compound is called a molecule.

Molecules are usually made of two or more atoms joined together.

APPLICATION 68. In the following list tell which things are elements, which are compounds, and which are mixtures, remembering that both solutions and alloys are mixtures:

Air, water, salt, gold, hydrogen, milk, oxygen, radium, nitrogen, sulfur, baking soda, sodium, diamonds, sweetened coffee, phosphorus, hydrochloric acid, brass.

INFERENCE EXERCISE

Explain the following:

431. Although in most electric lamps there is a vacuum between the glowing filaments and the glass, the glass nevertheless becomes warm.

432. Clothes left out on the line overnight usually become damp.

433. You can separate water into hydrogen and oxygen, yet you cannot separate the hydrogen or the oxygen into any other substances.

434. Wet paper tears easily.

435. Windows are soiled on the outside much more quickly in rainy weather than in clear weather.

436. If you stir iron and sand together, the iron will rust as if alone.

437. Rust is made of iron and oxygen, yet you cannot separate the iron from the oxygen with a magnet.

438. A reading glass helps you to read fine print.

439. Stretching the string of a musical instrument more tightly makes the note higher.

440. Mayonnaise dressing, although it contains much oil, can readily be washed off a plate with cold water.