Chemical Changes All About Us (Special Version, 1960)

[Music] Did you know that your kitchen at home is much like a chemistry laboratory. It's true. When mother makes a cake, she mixes together many substances, each one different from the others. Then she puts this mixture into the oven. In a very short time, there is a cake and it's very different from original substances. While a cake is baking, chemical changes are taking place. Let's find out more about chemical changes in a real laboratory. Here are two substances, sulfur and iron. They are elements. Elements are made of tiny bits called atoms. All substances are made of atoms, but elements are made of only one kind of atom. The element sulfur is a yellow powder. A magnet does not attract sulfur. We say these are properties of the element sulfur. Iron has different properties. A dark gray color and a magnet will attract iron. When iron and sulfur are mixed, they each keep their own special properties. This combination is called a mixture. Are the parts separate here? A magnet separates the magnetic iron filings from the non-magnetic sulfur in a mixture. Each substance keeps its own properties. Now let's heat the mixture of sulfur and iron filings. The elements are being changed. The mixture no longer looks like sulfur nor like iron. There is no yellow sulfur in the new substance. The iron is no longer pulled by the magnet. The properties of both the iron and sulfur have changed. A chemical change has taken place. A completely new substance iron sulfide has been formed by the chemical change. It's made of the elements sulfur and iron, but it's different from both of them. The new substance, iron sulfide, is called a compound. A chemical compound is made of tiny bits called molecules. A molecule is made of two or more kinds of atoms. Molecules of iron sulfide are made from atoms of iron and atoms of sulfur. Here is another chemical change. Let's mix water and calcium. A chemical change takes place. The element calcium and the compound water are forming a new substance. It's a chemical compound called calcium hydroxide. It was made from the element calcium and elements that were part of the water. This time we'll use two substances that are both compounds. The first is a compound called sulfuric acid. The second compound is table sugar. When the acid and sugar are combined, a new substance begins to form. You can see it looks completely different from either the acid or the sugar. Again, we can see that substances change their appearance when a chemical change takes place. Here we have an element magnesium. All around the magnesium is another element oxygen. Oxygen is a gas part of the air that we breathe. Here you see a familiar process. We are burning the magnesium. Yes, burning is a chemical change. It takes place when a substance combines with oxygen. The scientist calls this oxidation. This ash is a new compound called magnesium oxide. It was formed during burning or oxidation of magnesium. When substances combine rapidly with oxygen, scientists say rapid oxidation is taking place. Burning is rapid oxidation. But sometimes substances combined slowly with oxygen. Slow oxidation cause these rust spots to form on this piece of iron. You now know when there is a chemical change, substances change and different substances are formed. But something else happens during a chemical change. Just mixing sulfur and iron together, no chemical change took place. The iron and sulfur remained the same substances. How did we cause the chemical change to take place? We had to supply energy. In this case, we supplied more energy by heating. Then the chemical change took place and the atoms of iron and sulfur combined to form iron sulfide. Water and calcium do not need heat to cause the chemical change. In fact, we will find if we take the temperature of the water that heat is given off during this chemical change. Here the water temperature is about 70°. Now let's combine calcium with the water as we did before. As the chemical change takes place, the temperature begins rising. Now it's rising past 100°. Heat energy is being given off. So we've learned two things. During a chemical change, substances change and energy is either given off or taken in. Let's repeat the experiment with the sulfuric acid in the sugar. Is energy given off? Is it used? The sugar is at the temperature of the room and so is the acid. Watch the thermometer. The temperature is going up quickly. Why? As the chemical change takes place, heat is being given off. Magnesium has to be heated before it burns. Then it gives off much heat and light energy. So you see in some chemical changes heat is both used and given off. Our experiments have explained chemical changes. Chemical changes are all around us. Let's look at some chemical changes in our home. Baking a cake is a chemical change. A cake is made of many substances that are mixed together and then baked. One of the substances is a compound, baking powder. Let's see how a chemical change of baking powder is used in baking. When baking powder is mixed with water, what happens? A chemical change takes place. Bubbling gas is being formed from the water and baking powder. The gas formed in this chemical change causes batter like this to rise and form a cake like this. Let's light a match. When a match burns, a chemical change is taking place. The match gives off much heat and light energy. And when the chemical chain stops, what's left? It's a new substance, black carbon. Living things also depend on chemical changes. In a plant, water from the soil and carbon dioxide gas from the air combine in the leaves. This chemical change is called photosynthesis. The green substance in the leaves and the light energy of the sun cause a chemical change that turns the water and carbon dioxide into food for the plant. Many chemical changes take place in our bodies when we digest food. In our mouth, the compound starch that's in foods is changed to sugar, which our body can use. By means of X-ray motion pictures, you can see how the tongue mixes food with saliva. What happens to starch in our mouth? Here is water and here is saliva. Let's put a little starch in each liquid and mix it. You can test for starch with iodine. A very dark blue color is produced when iodine is mixed with starch. When we drop iodine in the dish of water and starch, the brown iodine produces a dark blue color which tells us that starch is in the water. But the brown iodine does not produce a blue color in the starch mixed with saliva. This means that the starch we put in has changed to something else. A chemical change has taken place. The starch has changed to sugar. Just as saliva change starch to sugar in our mouths, all living things, including plants and animals, depend on chemical changes for life and for growth. And chemical changes are going on about us all the time. Many machines depend on chemical changes in order to run. Automobile engines burn gasoline. This burning or rapid oxidation is a chemical change. It gives off energy. The energy drives the car. Taking pictures and developing them involves several chemical changes. To take a picture, we open the camera shutter for just a moment to let light strike the film. Light energy causes a chemical change in the chemicals that are part of the film. Later, after more chemical changes are made on special paper, we have a photograph. You now know that many chemical changes take place in solids, liquids, and gases. A mixture of elements made of atoms can be changed into a compound made of molecules. Two compounds or an element and a compound can also react chemically. Whenever chemical changes occur, substances change to form new substances. In chemical changes, energy is either given off or used. Chemical changes are very important and they're happening in you and all about you.