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CLASSROOM CONNECTORS TIME REQUIRED: one hour MATERIALS: Salt, piece of zinc, hydrochloric acid, Mg ribbon, nail, bottle of coke, candle, matches, heat source SIGNIFICANT TERMS: Chemical change, chemical property, property, physical change, physical property SET: Matter is generally described by giving its physical and chemical properties. Today we will discuss what these properties are and learn some common examples. INSTRUCTION: A property is a set of identifying characteristics about a substance. Physical properties are easy to identify because they involve your senses of sight, touch, taste, smell and hear. Common examples of physical properties include the color, size and texture of an object. The characteristics, however, are not enough to identify a material. Additional ones such as density, and freezing point are needed. Any slight change in these physical properties brings about physical changes such as when ice melts. The substance changes size, shape or state, but does not change into a new substance with new properties. One of the most common examples of a physical change is the melting of ice. Ice is solid H20; when it melts, it becomes liquid H20. Chemical properties are those properties a substance possesses because of its action or lack of action with other substances. Reaction with an acid, or reaction with oxygen (combustion) are just a couple of examples of chemical properties. Studying chemical properties is usually done when chemical changes are observed. A chemical change is a change in which one or more new substances with new properties is formed. When paper is burned, the ashes formed are entirely different from the original paper that was burned. Chemical and physical properties and changes are characteristic of every substance. See if you can identify the following as physical or chemical by creating a chart and marking each example under the proper category: 1. tearing a piece of paper (Physical) 2. burning wood (Chemical) 3. a candle 5 inches long (Physical) 4. boiling water (Physical) 5. adding hydrochloric acid to zinc (Chemical) ACTIVITIES: (In order to do some of the following, you may have to get chemicals from the high school chemistry department.) 1. Dissolve a small amount of salt in water. Is this a chemical change or a physical change? (Physical) Allow the solution to evaporate. Is this a chemical or physical change? (physical) 2. Add a small piece of zinc to 5 ml of hydrochloric acid. Is the reaction a chemical or physical change? (Chemical) 3. Burn a small piece of Mg ribbon by holding it with tongs in a flame until it catches fire. Do not observe directly. Is the change a chemical or physical one? (Chemical) 4. Put a small nail into a bottle of Coke and leave it for one week. Is the change a chemical or physical one? (Chemical) 5. Light a candle and allow it to burn five minutes. Extinguish. Is the change in the candle physical or chemical? (Physical) CLOSURE: We have discussed chemical and physical properties and changes. Turn to your neighbor and describe one physical and one chemical property of a substance. Then have your neighbor explain to you the difference between a physical and chemical change. GLOSSARY chemical change - a change in which a new substance with new properties is formed chemical property - a property that describes how a substance interacts or fails to interact with another physical change - a change in size, shape, or state that does not result in the formation of a new substance physical property - a property that relates to an object's size, shape, or state. These are determined by the senses. property - a set of characteristics that may help to identify the substance