Released Science Inquiry Task A Cool Investigation

Transcription

1 Date: Your Name: Released Science Inquiry Task A Cool Investigation 07 Grade Student Test Booklet

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3 Directions: Science You will be reading a story and analyzing the data provided to answer a set of questions. Read each question and thoroughly explain all of your answers. You may include labeled drawings or diagrams to help you answer the questions. This Word Bank provides definitions for words used in this task. You may refer back to this page throughout the session. Word Bank Calorimeter Compound Dissociation Solution a device for measuring the heat released or absorbed during a chemical reaction, change of state, or formation of a solution a pure substance composed of two or more types of atoms bonded in specific ratios the separation of an ionic compound into its individual charged ions by a chemical process, such as dissolving a substance dissolved in another substance to form a mixture

4 A Cool Investigation Eva arrives at science class with a swollen knee and a cold pack supplied by the school nurse. The pack instructions direct her to shake the pack for thirty seconds and then place the pack over a cloth or paper towel on the injured area for 0 utes. The cold temperature will help reduce the swelling in her knee. Instant Cold Pack Cold pack Paper towel Eva s classmates Victor and Jenna ask what makes the pack get cold. Eva thinks that a chemical change occurs inside the pack when she shakes it. Their teacher, Mr. Mayfield, tells the class that the pack is an example of one type of a chemical change the students have just studied called dissociation. He reds the class that dissociation happens when an ionic compound dissolves and separates into individual ions. Victor and Jenna identify the two cold pack ingredients as ammonium nitrate (NH NO ) and water (H O). Mr. Mayfield draws the following diagram to model the dissociation of ammonium nitrate in water. NH NO NH + + NO ionic compound (in water) ions dissolved in water The class discusses the compound and dissociation with Mr. Mayfield. The students conclude that when this compound dissolves in water it absorbs heat energy and cools the solution in the cold pack. Victor gets an idea and asks, Can we make our own cold pack by dissolving a compound in water to form a solution? The class can design an investigation to find out, Mr. Mayfield says. What kind of solution would make the best cold pack? he asks the students. It needs to get cold so it will absorb heat from the injury, says Jenna. But not too cold! Eva warns. It needs to stop cooling just above zero degrees Celsius to avoid harg the skin.

5 Those are both good observations, says Mr. Mayfield. He tells the class that he can supply four compounds for the students to try in designing their cold packs. After some research and a discussion, the class agrees on this question to investigate: Research Question: When dissolved in 00 milliliters (ml) of water, what compound in the smallest amount will decrease the solution s temperature to C? The class divides into four groups to investigate the research question. The four group names are Green, Blue, Orange, and Purple. The students decide that the groups will all follow the same procedures so that they can compare their results. They realize that they will need to do two investigations to answer the research question. In Investigation, each group will compare the same four compounds and choose the best compound to use for the cold pack. In Investigation, the students will detere how much of the chosen compound is needed for the cold pack to reach a imum of C and no colder. Mr. Mayfield tells the students that he will be providing them with samples of potassium nitrate, ammonium chloride, potassium chloride, and sodium nitrate. He instructs the students to do some background research on these compounds before they begin their investigations.

6 Background Research Through their research, the students learn that each of the four compounds produces a different temperature change when it dissolves in water. They find data that show the standard measured laboratory values for the heat absorbed or released by compounds dissolving in water. Mr. Mayfield helps the students use these values to calculate the expected temperature change of 0 grams (g) of each of their compounds in 00 ml of water. Each group records these values in Table. Table : Expected Temperature Change (0 g of compound dissolved in 00 ml water) Name and Formula Expected Change ( C) Potassium nitrate (KNO ). Ammonium chloride (NH Cl) 9.9 Potassium chloride (KCI) +8. Sodium nitrate (NaNO ) 8.7 Based on their research and calculations, the groups make the following predictions for the compound that will form the solution that reaches the lowest temperature: Green team: potassium nitrate Blue team: ammonium chloride Orange team: potassium chloride Purple team: sodium nitrate Answer question on page 0 in your Student Answer Booklet. q Identify which group s prediction about the solution that will reach the lowest temperature is supported by the data in Table. Describe how the data support this prediction.

7 Investigation In Investigation, each group will compare the same four compounds and choose the best compound to use for the cold pack. Working together, the groups create the following list of materials they need for the first investigation. Materials one simple calorimeter (thermometer, stirrer, cardboard lid, two foam cups) digital balance graduated cylinder two -liter bottles of C water teacher-supplied samples of four compounds at C paper towels Next, the students use the foam cups, cardboard lid, stirrer, and thermometer to create the simple calorimeter shown in Diagram. Thermometer Diagram : Foam Cup Calorimeter Stirrer Cardboard lid Two foam cups 00 ml water and compound solution inside inner cup 5

8 Finally, the groups of students agree to follow the procedure below.. Be sure you are wearing all necessary protective equipment.. Measure 00 ml of water with the graduated cylinder. Add the water to the inner calorimeter cup.. Measure the water temperature with the thermometer and record it in your data table.. Measure 0 g of the compound on the digital balance and add it to the 00 ml of water in the calorimeter. 5. Place the cardboard lid on top of the calorimeter. Insert the stirrer and thermometer through the two lid holes. 6. Stir the solution continuously. Measure the temperature of the solution once each ute for the next four utes. Record the temperatures observed in your data table. 7. Read and follow the disposal information Mr. Mayfield provides us with. 8. Ensure the cups, thermometer, lid, and stirrer are clean and wiped dry with paper towels. 9. Repeat steps 8 for the three remaining compounds. 6

9 Each group conducts Investigation. After recording their results, the students share their data as a class and calculate the average temperatures for the solutions they made with each of the four compounds. Their results are shown in Tables 5. Table : Potassium Nitrate (KNO ) Solution Group Green Blue Orange Purple Average 0 Temperature ( C) Table : Ammonium Chloride (NH Cl ) Solution Group Green Blue Orange Purple Average 0 Temperature ( C) Table : Potassium Chloride (KCI) Solution Group Green Blue Orange Purple Average 0 Temperature ( C) Table 5: Sodium Nitrate (NaNO ) Solution Group Green Blue Orange Purple Average 0 Temperature ( C)

10 Answer question on page 0 in your Student Answer Booklet. w Explain the most likely reason the students averaged the data from the four different groups. Support your explanation with evidence from the data in Tables 5. Answer questions and on page in your Student Answer Booklet. e Identify which group s data show the greatest amount of experimental error during Investigation. Use Tables 5 to describe a possible experimental error that may have produced the specific data results. Based on the results of Investigation, the students choose potassium nitrate (KNO ) as the best compound to use in the cold pack. r Use the specific data for each of the four compounds in Tables 5 from Investigation to justify the students choice of potassium nitrate (KNO ) as the best compound to use in a cold pack. Investigation In Investigation, the students will detere how much of the chosen compound is needed for the cold pack to reach a imum of C and no colder. The students will test four different amounts of potassium nitrate dissolved in 00 ml of water and record the temperature of the solutions each ute for the next four utes. The four groups conduct Investigation. Then the class averages the results of all four groups and records the data in Table 6, shown below. Table 6: Average Potassium Nitrate (KNO ) Solution Temperatures (dissolved in 00 ml water) Test Mass of Dissolved KNO (g) 0 Temperature ( C)

11 Answer question 5 on page in your Student Answer Booklet. t Create a graph that compares the average temperatures recorded by the class over four utes in Table 6 during Investigation. Be sure to include all required elements of a graph and choose a scale that will clearly show the data. After both investigations, Mr. Mayfield asks the students to discuss the results. We can make a cold pack that cools to C using potassium nitrate, Eva claims. I m not so sure, Victor wonders. We didn t match our final temperature of C. Answer question 6 on page in your Student Answer Booklet. y Explain why Eva s claim that the class can make a cold pack that cools to C using potassium nitrate is supported by the data in Table 6 even though Victor s statement that the class did not match the final temperature of C is true. Planning Further Investigations The students wonder how their results apply to making an actual cold pack. We know how potassium nitrate works in an insulated cup. Would we get the same results in an actual cold pack container that is not insulated? Jenna asks. The students want to perform an investigation with a potassium nitrate solution in a plastic bag instead of an insulated cup. They want to compare their results to the results from Investigation. Answer question 7 on page in your Student Answer Booklet. u Identify the three most important independent or controlled variables from Investigation that would need to be used in the new investigation to be able to compare the results of both investigations. Explain why using these variables would allow a fair comparison. 9

12 What if we needed a heat pack instead of a cold pack? asked Victor. Based on the data from the students investigations, a student predicts that a heat pack that reaches 0 C can be made from one of the four compounds. Answer question 8 on page in your Student Answer Booklet. i Explain how the evidence from both Investigation and Investigation support the prediction that a 0 C heat pack can be made from one of the four compounds. 0