Chemquest: Physical Changes or Chemical Reactions

Transcription

1 Chemquest: Physical Changes or Chemical Reactions Erik Misner May 9, 2005 Background: This lesson is designed to be an interactive and fun way to learn the difference between physical changes and chemical reactions. It provides indoor and outdoor lab activities to stimulate independent student thought, and blends high- and low-tech formative assessment using a computer based board game. After a brief video introduction to the criteria used to delineate physical changes and chemical reactions, students go outside, record, and characterize ten changes they observe in the environment. The next day, students explore ten lab stations to determine whether they are witnessing a physical change or a chemical reaction. Finally, students play Chemquest and fill out a standards-based vocabulary sheet. These provide formative and summative assessments, and help clear up any misconceptions students may be having. Teachers should know the difference between the evidence for a physical change versus the indicators for a chemical reaction. At the eighth grade level, I used a change in location, shape, size, or phase as evidence for a physical change. I used generation of a gas, change in color, absorption or release of heat, or formation of a precipitate as indicators of a chemical reaction. Vocabulary: ph A measure of the acidity of a liquid. Density The amount of matter per unit volume. Precipitate A solid substance that separates from a liquid. Boiling Point The temperature at which a liquid turns into a gas. Melting Point The temperature at which a solid turns into a liquid. Phase The state matter is in, such as solid, liquid, or gas. Evaporation When a thin layer of liquid molecules change into a gas. Expansion When matter increases in size, often due to being warmed. Reactivity How likely a substance is to take part in a chemical reaction. Condensation When a gas loses enough energy (cools) to become a liquid. Corrosion When metals change, often falling apart, due to chemical action. Solubility The amount of matter that can be dissolved in another substance. Objectives: The objective of this lesson is to teach some basic concepts regarding the properties and changes of properties in matter. Students will learn The evidence that matter has undergone a physical change. The evidence that matter has undergone a chemical reaction. How to identify the physical and chemical changes in their environment. Standards-aligned physical science vocabulary words. How to make and record careful scientific observations.

2 Standards: Arizona Grade 8- Strand 5- Physical Science Concept 1- Properties and Changes of Properties in Matter PO 1- Identify different kinds of matter based on the following physical properties: States Density Boiling point Melting point Solubility PO 3- Identify the following types of evidence that a chemical reaction has occurred: Formation of a precipitate Generation of gas Color change Absorption or release of heat Materials: Outdoor Lab Handouts Indoor Lab Handouts Safety Glasses (Sargent-Welch) Water (Grocery) Eyedropper bottles (Sargent-Welch) Baking Soda (Grocery) ph Paper (Sargent-Welch) Ice Cubes (Grocery) Paper (Staples) Vinegar (Grocery) Pencils (Staples) Alka-Seltzer Tablets (Grocery) Pencil Sharpener (Staples) Salt (Grocery) Drinking Glasses (Wal-Mart) Coffee Saucers (Wal-Mart) Chemquest Board (Website) Rusty Iron (Junkyard) Chemquest Cards (Website) Non-rusty Iron (Hardware) Game Tokens (Toy store) Limestone (Sargent-Welch) Clay (Toy store) Video ( Calcium Chloride (Sargent-Welch) Optional Cream of Tartar (Grocery) Optional Bromothymol Blue (Sargent-Welch) Optional Qt. Ziploc Bags (Grocery) Optional Saturat. Ca Acetate (Sargent-Welch) Optional Measuring Spoons (Grocery) Optional 250 ml Beakers (Sargent-Welch) Optional Hot plates (Sargent-Welch) Optional 10 ml Grad. Cyls. (Sargent-Welch) Optional Chemistry Handout Optional Sargent-Welch is a scientific supply company that carries a variety of supplies. Check them out online at or call them at The video I showed was entitled Matter and its Properties: Changes in Matter. I downloaded it from ASU s Asset site. It requires a paid membership, but it is worth it.

3 Time: This lesson plan can take up to five 50-minute class periods to complete, depending on whether you include the optional extensions. Day 1- Video and outdoor lab exercise. Day 2- Indoor lab exercise. Day 3- Vocabulary exercise and Chemquest board game. Day 4- Optional (exciting) indoor lab exercise. Day 5- Summative assessment. Grade Level: This lesson is designed for 8 th grade science students. Procedure: Day 1- Video and outdoor lab exercise 1. Show the class a short (~20 minute) video detailing the differences between physical changes and chemical reactions. 2. Distribute Outdoor Lab Handouts (a sample is provided) to students and take them outside to an area where they can observe changes in their environment. Places with birds or insects flying, trees or plants growing and water moving work quite well. 3. Have students complete handout, noting changes and making careful observations. Stress the importance of making impartial and unbiased observations, not inferences. 4. When students have noted ten changes, return to class. 5. Have students discuss whether changes were physical or chemical, referring to the characteristics in the video. Day 2- Indoor lab exercise 1. Prepare and label 10 stations as directed below: a. Pieces of paper to be torn into small pieces by students. b. An eyedropper bottle of vinegar to be dropped onto a coffee saucer containing a few teaspoons of baking soda. c. An eyedropper bottle of vinegar to be dropped onto a coffee saucer containing several small chunks of limestone. d. A container of salt, a teaspoon, and a drinking glass full of water so that students can dissolve the salt in the water. e. Several pencils and a pencil sharpener so that students can sharpen pencils. f. An eyedropper bottle of vinegar, an eyedropper of water, and some ph paper on a coffee saucer so that students can drop the liquids on the paper. g. A rusty piece of iron and a non-rusty piece of iron for the students to compare. h. Some clay for students to mold into various shapes. i. Drinking glasses filled with ice cubes and water for the students to observe. j. Alka-Seltzer tablets and a drinking glass of water for the students to combine. 2. Distribute Indoor Lab Handouts (a sample is provided) and safety goggles to students. 3. Inform students that they are to wear the safety goggles throughout the lab exercise.

4 4. Have groups of three students take turns visiting and interacting at each station for about 4 minutes. 5. Have students complete handout, making careful observations and determining whether changes are physical or chemical in nature. They should indicate what piece of evidence led them to their conclusion. Stress the making of unbiased observations. 6. When students complete the handout, collect them and grade them. You will have a chance to discuss errors with students as they play the Chemquest game the following day. Day 3- Vocabulary exercise and Chemquest board game 1. Load the Vocabulary page of the accompanying website in a web browser and print out enough copies of the vocabulary page for your class. 2. Load the Teachers page of the accompanying website in a web browser and examine the directions for printing out the game board and Chemquest cards. 3. Print out one game board and one set of cards for every three students in your class. 4. Gather one card set and three game tokens into a Ziploc bag for each team of three students. 5. When class begins, distribute vocabulary printouts and load up the Vocabulary web page on each student computer. 6. Have students follow vocabulary word hyperlinks to help them complete printouts. 7. If your classroom or computer lab doesn t have enough computers, worksheets can be completed with the aid of text book glossaries instead. 8. As students finish vocabulary printouts, have them read the rules for Chemquest on the Chemquest web page of the accompanying website. 9. Have students play rounds of Chemquest. Distribute prizes to the winners of individual games or of mini-tournaments. 10. As students play, discuss common errors you found on their Indoor Lab Handouts. Day 4- Optional (exciting) indoor lab exercise 1. Please see the Extension section of this lesson plan for procedure. Day 5- Summative assessment 1. Distribute Summative Assessment Exam to students. 2. Have students exchange papers and grade the questions aloud. 3. Allow students to ask questions to clarify any misconceptions. Evaluation: This lesson offers many opportunities to assess student performance and understanding of the subject matter. The responses students give on their worksheets can be used as a starting point for formative assessment. The Vocabulary exercise and Chemquest game also allow students an interactive way to learn from their mistakes, thus providing further formative assessment opportunity. Finally, a sample End Of Unit Quiz has been included to give ideas on how to structure summative assessment. I have found that allowing the students to correct each other s quizzes in class can clarify lingering misconceptions.

5 Extension: If your class has behaved well and obeyed all the safety rules during the outdoor and indoor lab activities, you may want to have the students perform the following activity to show some very exciting examples of chemical reactions. I have included an Optional Chemistry Handout to go along with the activity, which can be used for further formative or summative assessment. 1. Prepare the blue-green water referred to in Recipe 2 of the handout by adding just enough bromothymol blue to a half gallon of water to make it a dark-teal color. 2. Distribute Chemistry Handouts (a sample is provided) and safety goggles to students. 3. Inform students that they are to wear the safety goggles throughout the lab exercise. 4. Walk students through the three recipes, one at a time, allowing them to follow the directions on the Chemistry Handout. 5. Recipe 1 results in the Ziploc bag filling with gas and becoming cool to the touch. 6. Recipe 2 results in the Ziploc bag filling with gas, becoming warm to the touch, and changing from blue to white or yellow in color. 7. Recipe 3 (from Sheet 2 of the Chemistry Handout Excel spreadsheet) results in the Calcium Acetate precipitating out of solution. Although this is not truly a chemical reaction, it is a dramatic display of a precipitate forming. It is supposedly reversible, but I was unable to get the Calcium Acetate to re-dissolve by cooling the beaker. Therefore I don t see any harm in the students believing a chemical reaction is occurring. Use your best judgment. 8. Have the students complete the handouts, focusing on making careful, unbiased observations. 9. The completed chemical reactions are safe enough to dispose of by discarding the Ziploc bags in the trash, and pouring the sodium acetate solution down the drain. Acknowledgments: I would like to acknowledge the work of Dr. Brian A. Jerome of AGC/United Learning, from whom I borrowed the idea and worksheet designs for the Day 1 and Day 2 lab activities. Thanks to Geoff Adams of Salt River High School at the Salt River Pima Maricopa Indian Community for his assistance in developing the Day 5 summative assessment.