The Scientific Method Using Mystery Powders

Gail Gavin Chicago High School For Agricultural Sciences
3807 West 111th Street
Chicago IL 60655
(312) 535-2500

Objectives: The 6th grade student will be able to: 1. Utilize the scientific process to determine the physical and chemical properties of a variety of common substances. 2. Perform several chemical and physical tests for identifying substances. 3. To construct and compare data results to determine unknown substances and mixtures. Materials Needed: Distilled Water Toothpicks Possible Mystery Powders: Paper Cups Iodine Boric Acid Black Construction Paper Clothes Pins Sugar Lighter Vinegar Salt Candles/Holders Well Trays Baking Soda Magnifying Glass Droppers Baking Powder Paper Towels Aluminum Foil Flour Conductivity Tester If performing in classroom: Corn Starch Popsicle Sticks Large Pan Powdered Sugar (marked 1/8th in.) Squirt Bottles Powdered Milk Plaster of Paris Two Identically Gift Wrapped Boxes-possible contents: Candy Empty Aluminum Can Strategy: Use a gift wrapped box as a motivational technique to introduce the scientific process/method. Do activity "What's in the Box", correlating investigatory process with scientific method. Introduce second identical box to class. Ask question, because similar in appearance do they contain same contents? Again discuss scientific process of discovery. On large sheet of dark colored paper pour out sample of each mystery powder. Have students imagine that they are chemists and one of the important tasks of a chemist is to make observations of unknown substances. Every pure substance has a set of physical and chemical properties that distinguish it from other substances. A physical property of a substance is that which can be observed or described aside from its chemical properties. Examples of physical properties are color, state of matter (solid, liquid, and gas), texture, solubility, electrical conductivity, and melting point. A chemical property involves listing or identifying chemical characteristics of a substance. That is the substance's ability to react chemically with another substance and in the process create new physical and chemical properties. The only way to observe a chemical property is by performing the chemical change. Performing several tests, the students will examine ten different substances by observing and recording their reactions to three different liquids (water, vinegar, iodine), electrical conductivity, and the effects of heating. Pass out lab sheets and directions. Point out appropriate lab safety. Have students get into assigned groups. As this is a beginners lab have all necessary materials at their stations. TESTS: Senses: Ask students to use their senses of sight (with and without magnifying glass), touch, and smell. Record data. Solubility: Put equal amounts of each powder into wells. Add twenty drops of water. Sample questions: "Did powders dissolve? Is the water clear? Is it cloudy?" If solution is clear and substance has disappeared substance has dissolved. If cloudy, substance is insoluble. Record data. Electrical Conductivity: Utilize same tray wells. Place tester wires into each well. Make sure wires are cleaned after each test. Record data. Clean wells. Iodine: Repeat powder procedure. Dispense two drops of iodine into each well. Sample question: "Was there a change in color?" Record findings. Clean wells. Vinegar: Repeat powder procedure. Dispense two to four drops of vinegar. Sample question: "Did the powders fizz?" Record findings. Clean wells. A fizzing indicates a chemical reaction. Heat Test: Make a cup out of foil. Clip clothes pin onto cup. Place small amount of powder into cup. Place candle into holder and light. Holding clothes pin place cup over flame. Heat for up to two minutes if necessary. Repeat procedure for each powder. Sample questions: "Did any powders change? Form new substances? Give off an odor?" Record findings. Use only dry powders to avoid splattering. Upon completion of tests record findings on the board. Ask students questions about their findings. Were there any differences in the results? Discuss subjectivity, controls, variables, etc. Have students give an operational definition of the powders at this point. Example: "Powder two is a white, grainy, substance that fizzes with vinegar, turns iodine dark blue, does not dissolve in water and conducts electricity." As students continue further testing on these powders they will form a more solid conclusion. These Mystery Powders are a spring board to other labs such as testing for acids and bases, density, etc. As a final activity open up mystery boxes and compare their conclusions to what is actually in the box. This gives the students a feel of how scientists can identify and describe things they can not see. Performance Assessment: Combine non-reactive powders in equal proportions to make mystery mixtures. Have students rerun tests and record findings. Compare prior results to determine what mystery powders constitute their mystery mixture. References: Fitch, Dr. Thomas. Mystery Powders Unit Plan. Illinois State University.

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