Physical and Chemical Properties of Oxygen (page 2)
Design Your Own Experiment
- Photosynthesis is an energy-producing reaction in which sugar, water, and oxygen are synthesized, in the presence of chlorophyll and light, from carbon dioxide and water. Synthesis is the forming of more complex molecules from simpler ones. For example, starch molecules are synthesized from simple molecules of sugar.
- Corrosion, such as the rusting of iron, is the erosion and disintegration of a material. The rusting of an iron nail can be used to demonstrate the combination of iron atoms with oxygen atoms in the air to form iron oxide. The reaction for the rusting of iron is as follows:
- Does more oxygen speed up the oxidation (combination with oxygen) process? Use iron nails small enough to fit inside the bottle of oxygen gas previously collected. With steel wool, scrub the outside surface of two nails that have no rust on them. CAUTI0N: Use rubber gloves to protect your hands when handling the steel wool. Place one nail inside the bottle and secure the cap. Place the bottle and the second nail where they can remain undisturbed. Make daily observations of the nails for seven days.
- Does iron rust faster when wet? Does acid rain increase the rate of rusting? Determine the effect of water and acids on the rusting of iron by using three equal-size pieces of steel wool. Wet one piece with water, wet a second piece by dipping it in vinegar, and leave the third piece dry. Place the steel wool pieces on separate saucers and allow them to sit exposed to the air for two days. Use a chemistry text to interpret the sequence of reactions produced by the observed results. You could use photographs to represent the daily changes. Note: You could extend this experiment by having relatives and/or friends who live in different cities collect rainwater. Then you could compare the rusting of the pieces of steel wool after they are dipped in the different rainwater samples.
- Other metals combine with oxygen, but the reaction with some metals, like copper, may take years. This slow oxidation rate can be observed by organizing a roll of pennies by their dates. The older coins are usually browner in color than the newer coins (unless they have been washed or kept in protective coverings). You can display sample coins that show the change from a new shiny penny to an older brown-colored penny.
- Does heat speed up the oxidation process? Choose two shiny pennies. Place one penny in an aluminum saucepan and heat for two minutes on the stove. Allow the penny to cool before removing. Compare the color of the heated penny with that of the unheated penny.
Plants are major contributors to atmospheric oxygen. Demonstrate the role of plants in producing oxygen and the fact that oxygen is a colorless, slightly soluble gas. Fill a large-mouthed jar three-fourths full with water. Place water plants such as elodea inside a funnel and set the funnel, mouth side down, in the jar of water. The stem of the funnel should be above the water level in the jar. Fill a small bottle (or test tube) with water. Place your thumb over the mouth of this bottle and invert it over the stem of the funnel. The mouth of the bottle must be below the water level in the jar (see Figure 26.2). Place the entire setup in a sunny area. Observe as bubbles of oxygen rise from the water plants and collect in the small bottle. Oxygen gas is not very soluble in water; thus, the gas displaces the water inside the bottle. When the bottle is full of oxygen, cap it and save the gas collected for the following experiment on rusting.