Time Frame: 2 lessons (45 minutes each)

Transcription

1 TEKS-Based Activity for Grade 8 It s in the Bag! Description: In this activity, students measure temperature changes in endothermic and exothermic processes to illustrate interactions between matter and energy. Time Frame: 2 lessons (45 minutes each) Correlation to Texas Essential Knowledge and Skills: During this activity, students will be exposed to the following Texas Essential Knowledge and Skills: (8.10) Science concepts. The student knows that complex interactions occur between matter and energy. The student is expected to: (C) identify and demonstrate that loss or gain of heat energy occurs during exothermic and endothermic chemical reactions. Note: The TEKS listed here are the main content TEKS for this activity; however, this activity may also cover additional content and process skills included in other TEKS. Materials: Metric measuring spoons (1 set per student group) Zipper-type freezer sandwich bag (3 per student group) Baking soda (15 ml per student group) Calcium chloride dihydrate powder (15 ml per student group) Water (15 ml per student group) Universal indicator with interpretation chart (1 dropper bottle of solution per class) Clear plastic cups (3) Temperature probe (1 per student group) Marker (1 per student group) Colored pencils (3 different colors per student group) Graph paper (1 page per student group) Safety goggles (1 per student) Safety aprons (1 per student) It s in the Bag! student investigation pages (included at the end of this activity) Background Information: In this activity, the temperature change students observe in Bag 1 is an endothermic process in which heat is absorbed, whereas the temperature change in Bag 2 is an exothermic process in which heat is released. However, chemical reactions are not occurring in either Bag 1 or Bag 2, as the substances are simply being dissolved. The changes in temperature, then, are the result of a physical change and not a chemical reaction. Charles A. Dana Center at The University of Texas at Austin 1

2 When the contents of Bag 1 are added to Bag 2, a gas is produced, and the final substance has new properties. In this case, the temperature change observed when the contents of the two bags are mixed does result from a chemical reaction. The result is an exothermic chemical reaction. Advance Preparation: 1. Place enough baking soda, calcium chloride dihydrate powder, and water in three appropriately labeled plastic cups so that each student group will have 15 ml of each. 2. Set up a materials distribution center so that students can easily collect all the materials needed for this activity. 3. Make copies of It s in the Bag! student investigation pages for each group. 4. Give students an opportunity to practice using the temperature probes before beginning this learning experience. Temperature probes, rather than thermometers, should be used for the temperature readings because it allows for more frequent readings and therefore a better analysis of the resulting temperature changes. If thermometers are substituted for the probes, readings should be made at 20-second intervals, and the Temperature Over Time table should be adjusted accordingly. Nevertheless, more frequent readings made by the temperature probes are best for analyzing this investigation. Procedures: SAFETY: Students should wear eye protection and safety aprons. They should not taste or smell any of the materials. 1. Talk students through the investigation pages. Be sure that students note they will be recording temperature over a period of time. Be sure students are familiar with the use of temperature probes before they begin this activity. 2. Have students work in groups to complete the It s in the Bag investigation pages. Charles A. Dana Center at The University of Texas at Austin 2

3 It s in the Bag! Student Investigation Pages Part A Materials for Part A: Metric measuring spoons 1 zipper-type sandwich bag 10 ml baking soda (NaHCO 3 ) 10 ml calcium chloride (CaCl 2 ) 10 ml water Universal indicator Safety goggles Safety apron Procedures: SAFETY: Wear eye protection and a safety apron. Do not taste or smell any of the materials. In this activity you will combine chemicals to demonstrate how substances may chemically react to form new substances. 1. Add 10 ml of calcium chloride (CaCl 2 ) and 10 ml of baking soda (NaHCO 3 ) to the sandwich bag. Seal the bag and mix the two chemicals thoroughly by kneading the bag. Observe the contents of the bag and record your observations in Data Table Be ready to make immediate and constant observations during this step. Open the bag and add 10 ml of water and 4 drops of universal indicator. Quickly seal the bag and knead the bag to mix the contents thoroughly. Observe the contents of the bag for 3 minutes. Feel the bag every seconds. Does the temperature of the bag change? Record your observations in Data Table 1. Charles A. Dana Center at The University of Texas at Austin 3

4 Temperature Based on Touch Without water or indicator With water and indicator Color Temperature based on touch Other observations Charles A. Dana Center at The University of Texas at Austin 4

5 PART B: Materials for Part B: Metric measuring spoons 2 zipper-type sandwich bags 5 ml baking soda (NaHCO 3 ) 5 ml calcium chloride (CaCl 2 ) 5 ml water Universal indicator Temperature probe Marker 3 different colors of colored pencils Graph paper Safety goggles Safety apron Procedures: SAFETY: Wear eye protection and a safety apron. Do not taste or smell any of the materials. In the next part of this investigation, you will further analyze the mixing of substances to determine if a chemical reaction is occurring. Use this table to help analyze your results. Indicators of a Chemical Reaction Yes No Temperature change with no other changes Temperature change along with other changes Gas produced along with other changes Precipitate forms Color change occurs As shown in the Indicators of a Chemical Reaction table above, a change in temperature is not necessarily evidence of a chemical reaction. Dissolving salts in water can result in a temperature change, but it is not a chemical reaction. Other factors, such as the production of a gas or the formation of a precipitate, would need to be present. Charles A. Dana Center at The University of Texas at Austin 5

6 Remember: An exothermic reaction occurs in a chemical reaction when heat is released during the mixing of substances this feels like the substances are getting warmer. An endothermic reaction occurs when heat is absorbed during the mixing of substances in a chemical reaction this feels like the substances are getting cooler. 1. Label the sandwich bags 1 and 2. Add 5 ml of baking soda (NaHCO 3 ) to Bag 1 and add 5 ml of calcium chloride (CaCl 2 ) to Bag Add 5 ml of water to Bag 1. IMMEDIATELY insert the temperature probe and measure the temperature. Continue to take temperature readings at 10-second intervals for 2 minutes. Record the data you collect in the Temperature Over Time table. What happened to the temperature? Was a new product produced or did the original substance simply dissolve in water? Based on the information found in the Indicators of a Chemical Reaction table, was this a physical or a chemical change? Support your conclusion. 3. Add 5 ml water to Bag 2. IMMEDIATELY insert the temperature probe, and measure the temperature. Continue to take temperature readings at 10-second intervals for 2 minutes. Record the data you collect in the Temperature Over Time table. What happened to the temperature? Charles A. Dana Center at The University of Texas at Austin 6

7 Was a new product produced or did the original substance simply dissolve in water? Based on the information found in the Indicators of a Chemical Reaction table, was this a physical or a chemical change? Support your conclusion. 4. Add 3 4 drops of universal indicator to Bag 2 and record the ph measurement in the Temperature Over Time table. Add 3 4 drops of universal indicator to Bag 1 and record the ph measurement in the table. Compare the ph results of the two bags and describe what you know about their ph readings 5. Take 15 ml of the contents from bag 2 and add it to bag 1. IMMEDIATELY insert the temperature probe, and measure the temperature. Continue to take temperature readings at 10-second intervals for 2 minutes. Record this data in the Temperature Over Time table. What happened to the temperature? Was a new product produced or did the two substances dissolve? Based on the information found in the Indicators of a Chemical Reaction table, was this a physical or a chemical change? Support your conclusion. Charles A. Dana Center at The University of Texas at Austin 7

8 Temperature Over Time Time Bag 1 Bag 2 Bag O seconds 10 seconds 20 seconds 30 seconds 40 seconds 50 seconds 60 seconds 70 seconds 80 seconds 90 seconds 100 seconds 110 seconds 120 seconds ph Final color 6. Use graph paper to construct a graph of the temperature changes. Use the colored pencils to represent the results of Bag 1, Bag 2, and Bag What can you conclude about the temperature changes observed in each bag? Charles A. Dana Center at The University of Texas at Austin 8