Oxides Of Nitrogen (1959)

[Music] The first oxide of nitrogen to be considered in this film is nitrus oxide, probably better known as laughing gas, which has the formula N2O. In this test tube, we've placed about 15 g of ammonium nitrate, which when heated gently decomposes into nitrous oxide and water. Now the first bubbles that are rising in the tank are mostly air which is being driven out of the tube by the expansion of the air in the tube as heating takes place. As we heat the molten ammonium nitrate, it decomposes slowly. The bubbles that are rising are a mixture of nitrous oxide and steam. Since nitrous oxide is moderately soluble in cold water, this trough has been filled with warm water to decrease the solubility of the nitrous oxide. We will uh now demonstrate the solubility of nitrous oxide in cold water. This test tube has been filled with nitrous oxide uh in the tank. Now we'll carefully invert the tube and add 10 ml of cold water from the graduate. I'll now take this red pencil and mark the tube at the surface of the liquid. Now we'll shake vigorously and the nitrous oxide should be dissolving in the water. Now we'll transfer the tube to the trough. Remove the thumb. Replace the thumb. Bring the tube back outside. And you can now see that the water stands at a substantially higher level in the tube than it did before. The extra water has replaced the nitrous oxide which dissolved in the cold water. Nitrous oxide decomposes when heated to a moderate temperature into a mixture of nitrogen and oxygen. It is the only other common gas besides oxygen which will cause a glowing splint to burst into flame as we can illustrate on one of these bottles of gas that we have collected. Sulfur also burns vigorously. in nitrous oxide. We can ignite this small lump of sulfur. We'll now lower the burning sulfur into the bottle of nitrous oxide. The bright blue flame indicates that sulfur burns readily in this gas. The equations which have been illustrated in the section on nitrust oxide are as follows. First, we prepared the gas by heating ammonium nitrate with the production of nitrous oxide and water. Then after testing the solubility of nitrous oxide in water, the statement was made that nitrous oxide can be fairly easily decomposed by heating to yield nitrogen and oxygen. And this statement was tested by inserting a glowing splint which we can represent as carbon into the nitrous oxide. And we saw that the splint burst into flame with the production of carbon dioxide and nitrogen. Similarly, when burning sulfur was inserted into nitrous oxide, it burned rap more rapidly than an air. This time with the production of nitrogen and sulfur dioxide. We have seen previously that dilute nitric acid reacts with copper to form another oxide of nitrogen, nitric oxide, having the formula N O. In this flask, we've placed about 60 milliliters of water. And in this graduated cylinder, we have about 20 milliliters of concentrated nitric acid. When we add the nitric acid to the water in the flask, we now have about 80 milliliters of mixture. The volume of the acid has been increased four times. Its concentration reduced to 1/4. So this acid is now about four normal. In the flask we have copper turning. And as we add the nitric acid to the thistle tube. Nitric acid begins to react with the copper forming nitric oxide. In this close-up shot of the generator bottle, you can see the bubbles of nitric oxide rising from the copper. You should note that the gas above the liquid in the bottle is nearly colorless, indicating that the brown oxide of nitrogen NO2 is not being produced in any substantial quantity by this reaction. Since nitric oxide is quite insoluble in water, we can collect it in the trough without any special precautions. In this picture, the nitric oxide is displacing water from the bottle in the conventional fashion. We will collect two bottles and one small test tube full of the gas. And then we'll fill the larger test tube at the back of the tank about 1/2 full of nitric oxide. In order to demonstrate the relative insolubility of nitric oxide in water, we have here some nitric oxide uh confined in a test tube uh containing a small amount of water. Again, the level of the water has been marked with the red pencil. Now we can vigorously shake this tube bringing the gas and the water into intimate contact and then removing the finger from the tube underwater, replacing it. Returning outside, we see that a little water has entered the tube, but not nearly as much as before when we were using laughing gas. Nitric oxide is then comparatively insoluble in water. Nitric oxide is more stable than nitrous oxide and does not decompose at so low a temperature. Therefore, nitrous oxide uh will extinguish a a burning splint because the temperature of the combustion is inadequate to cause the gas to decompose. This bottle contains nitric oxide and as we insert the splint the splint is extinguished. This uh dep contains some burning sulfur from this bottle. And as with the splint, the temperature of the burning sulfur is inadequate to decompose the nitric oxide and the sulfur is extinguished. Red phosphorus, however, uh burns at a much higher temperature than either sulfur or the wooden flint and in fact at a sufficiently high temperature to decompose the nitric oxide into nitrogen and oxygen. Therefore, the red phosphorus will continue to burn in the nitric oxide. I've placed some phosphorus from this bottle in the defecating spoon and uh we will ignite this now over the Bunson burn. Notice the luminous white clouds of phosphorus penttoxide produced as the phosphorus burns. We'll now place the burning phosphorus in the nitric oxide. And you'll note that combustion is rapid, more rapid than in air. The equations involved in the nitric oxide experiment are as follows. First, we prepared nitric oxide by the oxidation reduction reaction between copper and dilute nitric acid yielding copper ion and nitric oxide. This gas was uh evolved rapidly by the reaction. Next, after testing the solubility of nitric oxide in water, we saw that this material is so stable that burning carbon does not react with it, nor does burning sulfur. We did see, however, that burning phosphorus generates a high enough temperature to cause nitric oxide to react. the products being the white powdery P205 and nitrogen. The uh third oxide of nitrogen to be considered is the compound in which nitrogen has an oxidation number of 4 plus commonly called nitrogen dioxide. The uh formula of this uh compound cannot be written in a simple fashion however with complete correctness because at high temperatures the gas density corresponds to that given by the formula NO2 and the color of the gas is dark brown. At rather low temperatures, the gas density corresponds to the dimeic form N204. And under these conditions, the gas is colorless. At room temperature, we actually have an equilibrium mixture containing both molecules of NO2 and N204. The gas at room temperature is brownish in color. So, we know that some NO2 molecules are present. For convenience then a chemist usually write the formula at room temperature as NO2 ignoring the fact that some N204 may be present. This gas is most commonly and easily prepared by the reaction of oxygen with nitric oxide. We can demonstrate this reaction of nitric oxide with oxygen as well as the high solubility of nitrogen dioxide in water with which it reacts to form nitric acid primarily. As we return to our pneumatic trough containing the test tube which has been half filled with nitric oxide from the mouth of this glass tube is bubbling a slow stream of oxygen. As we place the oxygen tube under the mouth of the test tube, you'll notice the dark brown color which forms inside indicating the presence of NO2. And then the rapid rise of the water in the tube as the highly soluble nitrogen dioxide rapidly dissolves in the water. In this situation, we have the paradoxical seemingly paradoxical case of adding one gas to another and ending up with virtually no gas at all. Of course, what has actually happened is that the nitrogen dioxide which is formed has dissolved in the water. Now the gas in the tube is essentially pure oxygen and as more oxygen is added it's just being collected now in the usual fashion. When colorless oxygen was added to the colorless nitric oxide in the tube, a rapid reaction took place producing the brown gas nitrogen dioxide. Then the water rapidly rose in the test tube because nitrogen dioxide dissolves in and reacts with water as indicated by this equation yielding a mixture of nitrus and nitric acids. This means then that the nitrogen dioxide left the gaseous state and as it did so water rose in the tube to replace it. In this film we've examined the three principal oxides of nitrogen nitrous oxide, nitric oxide and nitrogen dioxide. In each case we've observed how these gases may be prepared and we've studied some of the typical chemical reactions which they undergo. [Music]