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(1)CHEMISTRY(1'2)&2856( SUCCESS:. Changes TE.

(2) Chemistry End-of-Course Success Copyright Copyright © Texas Education Agency, 2011. The following materials are copyrighted © and trademarked ™ as the property of the Texas Education Agency and may not be reproduced without the express written permission of the Texas Education Agency, except under the following conditions: 1) Texas public school districts, charter schools, and Education Service Centers may reproduce and use copies of the Materials and Related Materials for the districts’ and schools’ educational use without obtaining permission from the Texas Education Agency; 2) Residents of the state of Texas may reproduce and use copies of the Materials and Related Materials for individual personal use only without obtaining written permission of the Texas Education Agency; 3) Any portion reproduced must be reproduced in its entirety and remain unedited, unaltered, and unchanged in any way; 4) No monetary charge can be made for the reproduced materials or any document containing them; however, a reasonable charge to cover only the cost of reproduction and distribution may be charged. Private entities or persons located in Texas that are not Texas public school districts or Texas charter schools or any entity, whether public or private, educational or noneducational, located outside the state of Texas MUST obtain written approval from the Texas Education Agency and will be required to enter into a license agreement that may involve the payment of a licensing fee or a royalty fee. For more information, contact: Office of Copyrights, Trademarks, License Agreements, and Royalties. Texas Education Agency. 1701 N. Congress Ave., Austin, TX 78701-1494; phone 512.463.9437; e-mail [email protected].. .

(3) CHANGES TE. Changes Lesson Overview Texas Essential Knowledge and Skills (TEKS) Chemistry TEKS with Student Expectations Scientific Processes Chemistry (1) The student, for at least 40% of instructional time, conducts laboratory and field investigations using safe, environmentally appropriate, and ethical practices. The student is expected to: (A) demonstrate safe practices during laboratory and field investigations; including the appropriate use of safety showers, eyewash fountains, safety goggles, and fire extinguishers; (B) know specific hazards of chemical substances such as flammability, corrosiveness, and radioactivity as summarized on the Material Safety Data Sheets (MSDS); and (C) demonstrate an understanding of the use and conservation of resources and the proper disposal or recycling of materials. Chemistry (2) The student uses scientific methods to solve investigative questions. The student is expected to: (E) plan and implement investigative procedures, including asking questions, formulating testable hypotheses, and selecting equipment and technology, including graphing calculators, computers and probes, sufficient scientific glassware such as beakers, Erlenmeyer flasks, pipettes, graduated cylinders, volumetric flasks, safety goggles, and burettes, electronic balances, and an adequate supply of consumable chemicals; (F) collect data and make measurements with accuracy and precision; (G) express and manipulate chemical quantities using scientific conventions and mathematical procedures, including dimensional analysis, scientific notation, and significant figures; (H) organize, analyze, evaluate, make inferences, and predict trends from data; and (I) communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings, graphs, journals, summaries, oral reports, and technologybased reports. Chemistry (3) The student uses critical thinking, scientific reasoning, and problem solving to make informed decisions within and outside the classroom. The student is expected to: (A) in all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student;. .

(4) CHANGES TE. Changes Lesson Overview Texas Essential Knowledge and Skills (TEKS) Chemistry TEKS with Student Expectations Science Concepts Chemistry (4) The student knows the characteristics of matter and can analyze the relationships between chemical and physical changes and properties. The student is expected to: (A) differentiate between physical and chemical changes and properties; (Readiness Standard) (C) compare solids, liquids, and gases in terms of compressibility, structure, shape, and volume; (Supporting Standard) Chemistry (8) The student can quantify the changes that occur during chemical reactions. The student is expected to: (D) use the law of conservation of mass to write and balance chemical equations; (Readiness Standard) Chemistry (11) The student understands the energy changes that occur in chemical reactions. The student is expected to: (A) understand energy and its forms, including kinetic, potential, chemical, and thermal energies; (Supporting Standard) (B) understand the law of conservation of energy and the processes of heat transfer; (Supporting Standard) (C) use thermochemical equations to calculate energy changes that occur in chemical reactions and classify reactions as exothermic or endothermic; (Readiness Standard). © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(5) CHANGES TE. Changes Texas College and Career Readiness Standards Science Standards for Chemistry with Performance Expectations I. Nature of Science: Scientific Ways of Learning and Thinking A. Cognitive skills in science 1. Utilize skepticism, logic, and professional ethics in science. 2. Use creativity and insight to recognize and describe patterns in natural phenomena. 4. Rely on reproducible observations of empirical evidence when constructing, analyzing, and evaluating explanations of natural events and processes. B. Scientific inquiry 1. Design and conduct scientific investigations in which hypotheses are formulated and tested. C. Collaborative and safe working practices 1. Collaborate on joint projects. 2. Understand and apply safe procedures in the laboratory and field, including chemical, electrical, and fire safety and safe handling of live or preserved organisms. 3. Demonstrate skill in the safe use of a wide variety of apparatuses, equipment, techniques, and procedures. D. Current scientific technology 3. Demonstrate appropriate use of a wide variety of apparatuses, equipment, techniques, and procedures for collecting quantitative and qualitative data. E. Effective communication of scientific information 1. Use several modes of expression to describe or characterize natural patterns and phenomena. These modes of expression include narrative, numerical, graphical, pictorial, symbolic, and kinesthetic. 2. Use essential vocabulary of the discipline being studied. II. Foundation Skills: Scientific Applications of Mathematics A. Basic mathematics conventions 6. Estimate results to evaluate whether a calculated result is reasonable. 7. Use calculators, spreadsheets, computers, etc., in data analysis. B. Mathematics as a symbolic language 2. Represent natural events, processes, and relationships with algebraic expressions and algorithms. F. Scientific measurement 1. Select and use appropriate Standard International (SI) units and prefixes to express measurements for real world problems. 2. Use appropriate significant digits.. .

(6) CHANGES TE. Changes III. Foundation Skills: Scientific Applications of Communication A. Scientific writing 1. Use correct applications of writing practices in scientific communication. B. Scientific reading 1. Read technical and scientific articles to gain understanding of interpretations, apparatuses, techniques or procedures, and data. 2. Set up apparatuses, carry out procedures, and collect specified data from a given set of appropriate instructions. 3. Recognize scientific and technical vocabulary in the field of study and use this vocabulary to enhance clarity of communication. V. Cross-Disciplinary Themes A. Matter/states of matter 2. Understand the typical states of matter (solid, liquid, gas) and phase changes among these. B. Energy (thermodynamics, kinetic, potential, energy transfers) 1. Understand the Laws of Thermodynamics. 2. Know the processes of energy transfer. C. Change over time/equilibrium 1. Recognize patterns of change. D. Classification 1. Understand that scientists categorize things according to similarities and differences. E. Measurements and models 1. Use models to make predictions. VII. Chemistry A. Matter and its properties 1. Know that physical and chemical properties can be used to describe and classify matter. 2. Recognize and classify pure substances (elements, compounds) and mixtures. H. Thermochemistry 1. Understand the Law of Conservation of Energy and processes of heat transfer. 2. Understand energy changes and chemical reactions. I. Properties and behavior of gases, liquids, and solids 1. Understand the behavior of matter in its various states: solid, liquid, and gas. 3. Understand principles of ideal gas behavior and kinetic molecular theory. 5. Know properties of liquids and solids. 6. Understand the effect of vapor pressure on changes in state; explain heating curves and phase diagrams. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(7) CHANGES TE. Changes Lesson Focus. The concepts developed in this foundational lesson are— physical and chemical changes; evidence of a chemical change; law of conservation of mass; law of conservation of energy; exothermic and endothermic processes; and phase changes.. 5E Lesson at a Glance. Engage (Cloud Model) Students observe a setup that models cloud formation. Observations will allow students to recall prior understanding about evaporation, boiling, condensation, freezing, and melting. Explore/Explain/Apply 1 (Physical and Chemical Changes) There are two parts to this investigation. In Part A, students study the changes in the exothermic reaction of sodium bicarbonate with calcium chloride. In Part B, students study the endothermic reaction of citric acid with sodium bicarbonate. The reactions are conducted in a sealable plastic bag so gas products are not allowed to escape. Both reactions are conducted in aqueous solutions. The masses before and after the reaction are measured and recorded. The changes, including changes in temperature, are qualitatively observed. Teacher demonstrations during the Explain section of the lesson assess student understanding of physical and chemical changes. Explore/Explain/Apply 2 (Phase Changes) Students heat a small quantity of ice over a hot plate. They trace the temperature changes as the solid ice changes to water and then into vapor. The use of calculators and probes is recommended for this investigation. Students acquire a basic understanding of energy changes that accompany phase changes. They will be able to read heating and cooling curves of substances and predict general shapes of graphs for phase changes. Elaborate (Changes) Students perform several chemical investigations. Each investigation allows the opportunity to apply laboratory process skills as well as understandings about physical and chemical changes. Students will observe and analyze their observations carefully to determine the attributes of the change. Independent student inquiry is emphasized. The Elaborate section may also be used as a performance assessment. Evaluate (Changes) All the expected learning outcomes are assessed using a written test. .

(8) CHANGES TE. Changes Material Safety Data Sheet Checklist Engage (Cloud Model). None. Explore/Explain/Apply 1 (Physical and Chemical Changes). Part A Calcium chloride (solid) Sodium bicarbonate (solid) Water Part B Citric acid (solid) Sodium bicarbonate (solid) Water Demonstration Copper (II) sulfate (solid) Sodium sulfate (solution) Barium nitrate (solution) Ammonium carbonate (solid) Dilute hydrochloric acid Sodium bicarbonate (solid) Potassium thiocyanate (solution) Iron (III) sulfate (solution). Explore/Explain/Apply 2 (Phase Changes). None. Elaborate (Changes). Sodium bicarbonate (solid) Vinegar Lead nitrate (solution 0.1 M) Potassium iodide (solution 0.1 M) Calcium chloride (solid) Soy wax Mineral oil Water. Evaluate (Changes). None. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(9) CHANGES TE. Changes Engage. Teacher Notes Investigate: Steam and Ice Students observe a setup that models cloud formation. Observations will allow students to recall prior understanding about evaporation, boiling, condensation, freezing, and melting. Learning Outcome • Describe different phase changes: evaporation, boiling, condensation, freezing, and melting. Advance Preparation Obtain ice and store in a cooler. Boil water in a 1 L beaker. Safety General lab safety rules apply due to the usage of glassware and hot liquids. Apparatus Setup for Each Student Group Pour about 100 mL of boiling water into a 250 mL beaker. Cover the beaker with a watch glass. Place a few ice cubes on top of the watch glass.. Activity 1. Place the setups on the tables, one for each student group. 2. Alert students to the safety hazards due to glassware and hot liquids. 3. Ask students to observe the apparatus carefully for a few minutes and record their observations on the Engage activity sheet. 4. Allow students time to discuss their observations and questions. 5. Ask students to write down their answers. 6. Monitor students during discussion and recording of responses. 7. Discuss the questions on the Engage activity sheet. 8. Accept all student answers.. .

(10) CHANGES TE. Changes Engage. Student Sample Accurate student answers are shown. Actual answers may vary.. Investigate: Steam and Ice 1. Observe the setup of the apparatus at your lab table. Discuss your observations with your group. 2. Discuss the following questions in your group and record in the space below. • Describe your observations. The beaker looks cloudy. The hot water is giving off steam. The ice on the cover is melting. Drops of water are trickling down the inside of the beaker. Water drops are forming on the underside of the watch glass and falling into the water. • What is a reasonable explanation for your observations? The water in the beaker is hot, and some of the water is changing into vapor. The water vapor cools when it touches the cold watch glass and changes into water drops. These water drops trickle down the sides of the beaker or fall back into the beaker from the bottom of the watch glass when they are large enough. The ice on the watch glass gains heat from the steam below and begins to melt. • What are the similarities and differences between evaporation and boiling? Evaporation and boiling are ways in which a liquid changes to a vapor. Evaporation takes place on the surface, whereas boiling takes place throughout the liquid. Also, evaporation occurs at any temperature, whereas boiling occurs at high temperatures or at a specific temperature. • What are the similarities and differences between freezing and melting? Freezing is the change of a liquid to a solid. Melting is the change of a solid to a liquid. Freezing and melting temperatures are the same for a given substance. For example, ice melts at 0 °C and also freezes at 0 °C. • What is the relation between boiling temperature and condensation temperature? Boiling is the change of liquid to vapor, and condensation is the change of vapor to liquid. Boiling temperature and condensation temperature are the same. For water, this temperature is 100 °C.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(11) CHANGES TE. Changes • What kind of change did you observe? How do you know? Physical change—no new substances were formed. Ice, water, and steam are all the same chemical substance: water.. .

(12) CHANGES TE. Changes Explore/Explain 1 Teacher Notes. Investigate: Changes in a Bag There are two parts to this investigation. In Part A, students study the changes in the exothermic reaction of sodium bicarbonate with calcium chloride. In Part B, students study the endothermic reaction of citric acid with sodium bicarbonate. The reactions are conducted in sealable plastic bags so gas products are not allowed to escape. Both reactions are conducted in aqueous solutions. The masses before and after the reaction are measured and recorded. The changes, including changes in temperature, are qualitatively observed. Teacher demonstrations during the Explain section of the lesson assess student understanding of physical and chemical changes. Learning Outcome • Categorize reactions as exothermic or endothermic based on the observed changes in temperature. • Observe evidence/indicators of a chemical change. • Categorize processes as physical or chemical changes based on valid reasoning. • Use the law of conservation of mass to predict unknown masses in a physical or chemical change. • Use the law of conservation of energy to explain energy changes in endothermic and exothermic processes.. Materials List For each student group • Chemicals for Part A: calcium chloride, sodium bicarbonate, water • Chemicals for Part B: citric acid, sodium bicarbonate, water • Weighing paper • Balance • 2 heavy-duty freezer bags • Plastic cup half-filled with tap water • 4 disposable pipettes • Empty plastic cup. Advance Preparation Prepare copies of MSDS sheets for all chemicals used in the investigation. Collect lab equipment and materials. Place lab equipment and materials for each student group on the table. Prepare demonstration materials as needed. Safety Chemical lab safety rules and general lab safety rules apply.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(13) CHANGES TE. Changes Activity (For Both Parts A and B) 1. Ask students to study the MSDS of the chemicals in each section of the investigation, discuss the safety in their lab groups, and write down the safety precautions in the safety box before beginning the investigation. 2. Review laboratory safety rules that apply to this investigation (Questions 1–4). 3. Ask students to read the instructions, perform the investigation, record the data, and discuss and write down responses to the analysis questions. 4. Allow student groups enough time to complete their investigations. Monitor students and the learning process. 5. Allow students to discuss their results in their groups and record their analyses and conclusions. 6. Lead discussion through questioning, using probing questions as needed to achieve the learning outcomes for this section of the lesson. The scripted questions below may be used as a guide to drive class discussion.. Discussion Questions 1. In Part A, what chemicals are used? sodium bicarbonate, calcium chloride, and water 2. Based on the MSDS, what safety precautions are needed for Part A? Both sodium bicarbonate and calcium chloride have a hazard rating of one, or low hazard, while water has a zero rating. General chemical lab safety rules and personal safety rules apply. Goggles and aprons must be worn, and hands must be washed before leaving the lab. 3. In Part B, what are the chemicals used? sodium bicarbonate, citric acid, and water 4. Based on the MSDS, what safety precautions are needed for Part B? Both sodium bicarbonate and citric acid have a hazard rating of one, or low hazard, while water has a zero rating. General chemical lab safety rules and personal safety rules apply. Goggles and aprons must be worn, and hands must be washed before leaving the lab.. .

(14) CHANGES TE. Changes Part A 5. What were some of the changes that you observed? Sodium bicarbonate was a fine white powder. Calcium chloride was also white but had granules that looked like tiny beads. The third chemical was water, a clear liquid. When all the chemicals were put together, bubbles formed, the solids started to mix with the water, and the plastic bag became very hot. 6. Was the change a physical or chemical change? The change was a chemical change. 7. How do you know? Gas was given off, and the solution in the bag became hot. These observations indicate that new material has been formed with different properties. One new substance is the new gas. 8. How did the temperature of the contents in the bag change? There was a rise in temperature. 9. Why do you think the temperature increased? Heat was released in the chemical change, and this heat was absorbed by the water/liquids. At this time, introduce the concept of energy conservation through the example followed by the statement of the law of conservation of energy: heat produced in change = heat used to raise the temperature of the contents Energy cannot be created or destroyed in a physical or chemical change. 10. What term is used to refer to a change where heat energy is released? exothermic (meaning heat exiting from the process) Part B 11. What were some of the changes that you observed? Sodium bicarbonate was a fine white powder. Citric acid was a white crystalline powder. The third chemical was water, a clear liquid. When all the chemicals were put together, bubbles formed, a clear solution formed, and the plastic bag became very cold. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(15) CHANGES TE. Changes 12. Was the change a physical change or chemical change? The change was a chemical change. 13. How do you know? Gas was given off, and the solution in the bag became cold. These observations indicate that new material has been formed with different properties. 14. Was the change absorbing heat or releasing heat? How do you know? The change in Part B was absorbing heat because there was a decrease in temperature of the solution in the bag. 15. What would be the energy conservation equation for this change? heat lost by contents = heat absorbed by the chemical change 16. What term is used to refer to a change where heat energy is absorbed? endothermic (meaning heat taken into the process) 17. How do you know if a new substance has been formed? Gas bubbles may be produced. There may be a color change or new material produced. The temperature may change, etc. At this time, a few teacher demonstrations may be performed to test student understanding before itemizing the indicators of a chemical change. Some suggestions are identified below. These changes may be substituted with other chemicals that produce similar results. Perform the reactions in test tubes in full visibility of all students. Allow students time and opportunity to observe the properties before and after the process, including visual, olfactory, and tactile observations. After each demonstration, ask students to identify if the change is physical or chemical and if it is exothermic or endothermic. The students must validate their identification by giving reasons for their classification. Suggestions for demonstrations • Physical change—Copper (II) sulfate crystals added to water in a test tube. Students often think that there is a color change and that therefore, this is a chemical change. If that happens, draw attention to the solid and its color. • Chemical change—Sodium sulfate solution added to barium nitrate solution. A thick white precipitate is formed. The term precipitate may be introduced at this point. • Chemical change—Warm solid ammonium carbonate in a test tube in a hot bath. The odor of ammonia is detected. Students may have to move up to be able to smell the gas. .

(16) CHANGES TE. Changes • Chemical change—Add dilute hydrochloric acid to baking soda solution. This results in vigorous gas evolution. This is also an endothermic change. • Chemical change—Add potassium thiocyanate solution to iron (III) sulfate solution. Yellow solution turns deep red, indicating a color change but no precipitate formation. 18. What are the indicators of a chemical change? The indicators of a chemical change are gas evolution, precipitate formation, color change, odor change, and temperature change. 19. Of the indicators, which is the least reliable indicator of a chemical change? Why? Temperature change is the least reliable indicator of a chemical change. A hot substance can cool down and have a temperature change, but that is a physical change. Sometimes a solid dissolving in a liquid can produce a temperature change, but that is also a physical change. Emphasize that in a chemical change, the chemical composition of the reactants changes as products are formed. 20. What term is used to refer to chemicals in a chemical change? Reactants are chemicals that enter a chemical change, and products are the chemicals formed at the end of the change. 21. What is another term for chemical change? chemical reaction 22. In Parts A and B, how did the mass before the change compare with the mass after the change? The mass stayed the same (or almost the same). 23. What is the law that states that the mass before the change equals the mass after the change? The law of conservation of mass states that the total mass of the substances remains constant during a change. Total Mass of Reactants = Total Mass of Products 24. How would the mass be affected if the plastic bag were not sealed? If the bag were not sealed, the gas produced in the change would escape into the air. The mass after the change would be less than the mass before the change.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(17) CHANGES TE. Changes Explore/Explain 1 Student Sample. Accurate student answers are shown. Actual answers may vary. Investigate: Changes in a Bag Part A Safety Study the MSDS for the chemicals used in Part A. Discuss safety precautions that must be used and list them in the space below. Sodium bicarbonate is slightly toxic. Calcium chloride is also slightly toxic. Goggles and aprons are needed. Avoid contact with eyes, skin, and clothing. Hands must be washed after completing investigation.. 1. Place 1.0 g of sodium bicarbonate into one corner of a plastic bag. 2. Place 1.5 g of calcium chloride into the other corner of the same bag. 3. Fill two disposable pipettes with water and place them in the plastic bag. Seal the plastic bag. 4. Observe the contents of the bag and record observations in the table on the following page. 5. Carefully place the sealed bag in a plastic cup. Place the cup with its contents on a balance. Measure the mass of the system and record this mass in the table on the following page. 6. Lift the bag and, from the outside, gently squeeze the pipettes inside the closed bag. Spill the water into the sealed bag and place the bag onto a tabletop. Mix the substances in the bag by squeezing gently. 7. Observe all changes inside the plastic bag. Write down your observations in the table on the following page. 8. Place the sealed bag in the same plastic cup and measure the mass of the system once again. Record this mass. 9. Clean up by disposing of the sealed plastic bag in the trash. 10. Proceed to Part B of your investigation.. .

(18) CHANGES TE. Changes Observations Before addition of water Sodium bicarbonate description Calcium chloride description Water description Mass of system. Fine white powder White, granular/ beadlike solid Clear liquid. After addition of water Some solid material dissolves in the water. Gas bubbles form and the bag swells up. Milky white liquid is left. Temperature rises and the contents of the bag feel hotter than before.. 21.52 g. 21.52 g. Part B Safety Study the MSDS for the chemicals used in Part B. Discuss safety precautions that must be used and list them in the space below. Sodium bicarbonate is slightly toxic. Citric acid is also slightly toxic. Goggles and aprons are needed. Avoid contact with eyes, skin, and clothing. Hands must be washed after completing investigation.. 11. Place 1.0 g of sodium bicarbonate into one corner of a plastic bag. 12. Place 1.0 g of citric acid into the other corner of the same bag. 13. Fill two disposable pipettes with water and place them in the plastic bag. Seal the bag. 14. Carefully place the sealed bag in a plastic cup. Place the cup with its contents on a balance. Measure the mass of the system and record this mass in the table on the following page. 15. Lift the bag and, from the outside, gently squeeze the pipettes inside the closed bag. Spill the water into the sealed bag and place the bag onto a tabletop. Mix the substances in the bag by squeezing gently. 16. Observe all changes inside the plastic bag. Write down your observations in the table below. 17. Place the sealed bag in the same plastic cup and measure the mass of the system once again. Record this mass. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(19) CHANGES TE. Changes 18. Clean up by disposing of the sealed plastic bag. 19. Discuss the questions in your group and record responses in the analysis section. Observations Before addition of water Sodium bicarbonate description. Fine white powder. Citric acid description. White crystalline powder. Water description. Clear liquid. Mass of system. After addition of water. 22.11 g. Bubbles of gas form. Clear liquid results. Temperature drops, and the contents of the bag get cold.. 22.10 g. Analysis and Conclusions: Parts A and B 1. Was the change in Part A a physical or chemical change? How do you know? The change in Part A was a chemical change because a new gas formed and the temperature rose. 2. Was the change in Part B a physical or chemical change? How do you know? The change in Part B was a chemical change because a gas was released and the temperature dropped. 3. Define physical change and chemical change in your own words. A physical change does not produce a new substance with different properties from the starting substance. The original material can be retrieved after the change. A chemical change produces new material with different properties from the starting materials. After a chemical change, the original material cannot be retrieved using simple methods.. .

(20) CHANGES TE. Changes 4. What are some indicators of a chemical change? Some indicators of a chemical change are change in temperature, gas bubble production, and new material produced with a different color/ different properties. 5. Were the changes endothermic or exothermic? How can you tell? Part A was an exothermic process because the heat given off caused the temperature of the water to rise. Part B was endothermic because the heat in the water was absorbed by the chemical change, resulting in a lower temperature of the water. 6. How did the mass before mixing of the contents in the bag compare with the mass after mixing? The total mass before the change was approximately equal to the total mass after the change.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(21) CHANGES TE. Changes Notes: Physical and Chemical Changes A chemical change produces new products. The chemical nature of the reactants may be different from the products. In a physical change, the chemical nature of the substance going through the change remains the same, even though it may look different. For example, when water changes to vapor, it looks different, but you can cool the vapor and condense it back to water. Indicators of a chemical change are gas formation, precipitate formation, color change, odor change, and temperature change. The least reliable indicator is the temperature change. (Temperature change can occur in physical change as well.) Chemical change is often called a chemical reaction. Substances entering a chemical change/reaction are called reactants. Substances produced in a chemical change/reaction are called products. Any process or change that takes in heat energy is endothermic. Any process or change that gives off heat energy is exothermic. When a change takes place in water/solution, the heat given off in the chemical reaction is absorbed by the water and the temperature of the water goes up (exothermic reaction). heat given off by the reaction = heat absorbed by the water In the same way, if heat is needed for a reaction, it is absorbed from the water and the temperature of the water drops (endothermic reaction). heat absorbed by the reaction = heat lost by the water This law is called the law of conservation of energy. Examples: Burning wood is a chemical change that is exothermic. Melting ice to make hot water is a physical change that is endothermic. In both physical and chemical changes, the mass before the change remains the same even after the change. This law is called the law of conservation of mass.. .

(22) CHANGES TE. Changes Application: Physical and Chemical Changes 1. Identify the change in each scenario described below as physical or chemical and endothermic or exothermic. Give reasons for your identification. Physical or Chemical. Endothermic or Exothermic. Chemical Precipitate is formed. Neither No temperature change. Chemical Gas released. Exothermic Temperature increases. When two clear colorless liquids are mixed, a clear colorless 3 liquid is formed. There is a decrease in temperature.. Physical No new substance formed. Endothermic Temperature decreases. When two clear colorless liquids are mixed, a clear pink 4 solution forms. There is no significant change in temperature.. Chemical Change in color is observed. Neither No temperature change. A warm, clear liquid changes to a clear, 5 crystalline solid at room temperature.. Physical No clear indicator of chemical change (may be freezing of a liquid to a solid). Endothermic Temperature decreases. Scenario When two clear colorless liquids are mixed, a yellow precipitate forms and 1 settles to the bottom of the test tube. There is no significant change in temperature. When two clear colorless liquids are mixed, gas bubbles 2 escape out of the test tube. There is an increase in temperature.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(23) CHANGES TE. Changes 2. In which type of change is mass conserved? Mass is always conserved in any change—physical as well as chemical. 3. Describe a situation when observations may indicate that mass is not conserved in the change. (diagrams allowed) It may appear that mass is not conserved if a gas product is allowed to escape. This situation will show a loss of mass. For example:. Mass before heating = 100.0 g. Mass after heating = 98.6 g. .

(24) CHANGES TE. Changes Explore/Explain 2 Teacher Notes. Investigate: Phase Change Students heat a small quantity of ice over a hot plate. They trace the temperature changes as the solid ice changes to water and then into vapor. The use of calculators and probes is recommended for this investigation. Students acquire a basic understanding of energy changes that accompany phase changes. They will be able to read heating and cooling curves of substances and also predict general shapes of graphs for phase changes. Learning Outcome • Use probes, CBL 2™, and calculators in interface to collect and graph data. • Analyze graphed data and report valid conclusions. • Describe the characteristics of a phase change in terms of physical properties and energy loss or gain. Advance Preparation Place lab equipment and materials for each student group on the table. Obtain ice and store in a cooler. Perform the investigation to adjust hot plate settings, time intervals, and duration of the experiment according to the available equipment.. Materials List For each student group • 4–5 ice cubes in a beaker (about 50 g of ice) • Hot plate • Magnetic stirrer • Clamp stand • Clamp • Calculators • CBL 2™ • Temperature probes • Graph paper (if needed) • HotHands® • Plastic cup with water. Activity 1. Ask students to review the procedure, discuss the safety precautions that are applicable, and write down the safety precautions in the safety box. 2. Review laboratory safety rules that apply for this particular activity. 3. Show students the proper setup for the investigation. (Ensure that the student groups have the proper setup before they receive their ice samples.) 4. Allow student groups to complete their investigations and discuss the analysis questions. 5. Monitor students and the learning process. 6. Graphs may be manually drawn or created with a graphing calculator.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(25) CHANGES TE. Changes 7. Review student responses to the analysis questions. Accept all answers at this time. (This allows the teacher to estimate the understanding developed independently by the students.) 8. Before class discussion, have each student group draw the general shape of their graph on the board. They may use different colored markers. 9. Lead discussion through questioning, using probing questions as needed to achieve the learning outcomes for this section of the lesson. 10. The scripted questions below may be used as a guide to drive class discussion.. Discussion Questions 1. What is the independent variable in your investigation? time intervals (10 second intervals) 2. What is the dependent variable in your investigation? temperature in Celsius. Temperature °C. At this time, draw on the board the X and Y axes as follows:. Time Intervals (Every 10 Seconds). 3. Did the water contain more heat at the first time interval or at the 50th? Why? The water contained more heat at the 50th interval because we continued the heating throughout.. Temperature °C. At this time, draw on the board the X and Y axes as follows:. . . Heat Energy.

(26) CHANGES TE. Changes 4. Can the graph also be represented as this one? Why? Yes, the two graphs are essentially the same if the amount of heat provided by the hot plate is constant. Emphasize that the setting of the hot plate was not altered during the investigation, so the amount of heat per second provided by the hot plate was constant. This step is important because students will see the Temperature versus Heat Energy graph in other resources.. 5. What do you notice about all the graphs drawn by student groups? They have a similar shape. 6. Describe the shape of the graph. (Answers will vary but the description will fit the shape shown below.) . 7. Based on this shape, how does the temperature of the ice change as it is continually heated? The temperature remains the same for some time, then increases rapidly, and finally remains the same. Label the three sections of the graph using letters. C. B A. 8. What do you think is happening in Section A of the graph? The ice appears to be melting into water. 9. What do you think is happening in Section B of the graph? The water is getting hotter. 10. What do you think is happening in Section C of the graph? The hot water is boiling.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(27) CHANGES TE. Changes 11. Why do you think the temperature is constant during melting even though we continued to heat? In the solid phase, the particles are close together and are vibrating, but not rapidly. The heat given is used to first move the particles apart and then to increase the motion of the particles. When the heat energy is used to move the particles apart, the temperature remains constant. 12. Why do you think the temperature is constant during boiling even though we continued to heat? The particles in the gas phase are further apart than in the liquid phase. The particles are moving more rapidly and sliding past each other. The heat given is used to first move the particles apart so the gas particles are no longer in contact with each other. During this boiling phase, the temperature remains constant. 13. Define melting, freezing, boiling, and evaporation. Melting is the change of a solid to a liquid. Freezing is the change of a liquid to a solid. Boiling is the change of a liquid to a vapor. It takes place throughout the body of the liquid. Evaporation is the change of a liquid to a vapor from the surface of the liquid. 14. What is the melting temperature of ice based on your data? close to 0 °C 15. What is the freezing temperature of water based on your data? close to 0 °C 16. Compare and contrast melting and freezing. Melting is endothermic, whereas freezing is exothermic. In melting, solid particles change into liquid particles. In freezing, liquid particles change into solid particles. The mixture of solid and liquid particles during freezing is identical to the mixture of solid and liquid particles during melting. So the freezing temperature is the same as the melting temperature. 17. Compare and contrast evaporation and boiling. Both processes involve a change of liquid into vapor. Evaporation can take place at any temperature when a liquid particle acquires enough energy to move into a gas phase. Boiling is the change of liquid particles into gas or vapor, essentially, throughout the body of the liquid.. .

(28) CHANGES TE. Changes At this time, introduce the term vaporizing as another word for boiling. Perform a teacher demonstration to illustrate the energy changes and movement of particles during phase changes. Teacher Demonstration Place some tiny foam balls in an empty plastic container with a lid. (Tennis ball containers or dry water bottles work well.) Make air holes in the container to allow for the release of air. Make a small opening in the lid and insert one end of the straw through it. Place the lid on the plastic container with the foam balls in it. This apparatus now represents a model of matter. Tell students that the foam balls represent matter in the solid state and that your exhalation represents the addition of heat energy. Blow gently through the straw and steadily increase the force of the air. The foam balls begin to move and get dislocated to other areas. This would simulate the transition of a solid to a liquid and then to a gas/vapor. After the students have had a chance to observe, stop blowing and tap gently on the sides to get the foam balls or particles back to the starting position.. 18. What do you observe when energy is given to the solid? The foam balls or the solid particles separate, then begin to move. 19. Is the process endothermic or exothermic? The process is endothermic because energy is absorbed. 20. What phase is represented when the foam balls move slightly away from each other? phase change or melting phase (The boiling phase is less observable in this model.) 21. What phase do the moving foam balls represent? liquid or vapor phase. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(29) CHANGES TE. Changes 22. What happens as the particles lose energy? The movement of the particles is reduced and they move back to the phase with lower energy; that is, from vapor to liquid or liquid to solid. 23. At this point, draw the axes below. If we had ice at –20 °C and started heating it in a closed container to collect the vapor, how would the graph look? Ask students to draw and label the parts of the graph. . Temperature °C. liquid vaporizing. vapor heating. liquid heating solid melting. solid heating. Heat Energy. 24. Explain how mass is conserved in a phase change. The law of conservation of mass applies to a phase change/physical change. The mass of the solid equals the mass of the liquid and the mass of the vapor if collected. 25. Explain how energy is conserved in a phase change. The law of conservation of energy applies to a phase change. Energy absorbed by ice as it changes from solid to liquid to gas is the same amount of energy lost by the gas as it changes to solid. (Answers may vary.) At the end of the discussion, allow students time to take notes on the important points discussed.. .

(30) clamp stand. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED. hot plate with magnetic stirrer. temperature probe in channel 1. temperature probe in icy water. CBL 2™ in cradle. cable connector from CBL 2™ to calculator. Setup of Equipment . CHANGES TE. Changes. .

(31) CHANGES TE. Changes Setup of calculator program for data collection (with teacher notes) then Select DataMate to enter the data collection program then to clear previous data Check that temperature is displayed in Celsius (if not, ask for assistance from your instructor) Press 1 for SETUP to change the time graph. If temperature in Celsius is not displayed, check then links, Sometimes . calibration may be needed.. Scroll down using the arrow keys to Mode: TIME GRAPH then. Press 2: TIME GRAPH to change the mode of the time graph Press 2: CHANGE TIME SETTINGS to change the time settings. Using the number keys, enter 10 seconds as the time between samples then. Confirm that the recommended times work well for the available equipment by conducting a run-through of the investigation. Adjust time intervals and number of samples if needed.. .

(32) CHANGES TE. Changes Using the number keys, enter 90 as the total number of to see the samples, then TIME GRAPH SETTINGS. Your data collection should take no more than 900 seconds.. Press 1: OK to confirm changes to data collection settings Press 2: START to start data collection. Graph will be displayed after data collection is complete then screen. to get to main. Press 6: QUIT then to return to calculator screen. Disconnect calculator from CBL 2™ to study and Press analyze the graph of data. Data collection is complete. Follow the instructor’s directions in saving your data and completing your laboratory report.. Differentiation in analysis of graph: • Students can analyze the graph displayed in the DataMate program without exiting to the calculator. A sketch of the graph may be recorded by the student. • Analyzing the graph outside the DataMate program is recommended so students can progress gradually into more complex regression analysis within the course.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(33) CHANGES TE. Changes. The data from the DataMate program are stored in the calculator. The data lists may be retrieved using then 1: Edit.. The graph may be retrieved using %. If graph is out of then 9: ZoomStat should bring graph into scale, focus.. Students may locate points on the graph by using the and arrow keys.. .

(34) CHANGES TE. Changes Explore/Explain 2 Student Sample. Accurate student answers are shown. Actual answers may vary. Investigate: Phase Change 5. 6. 5. 6. 4. Safety Study the procedure that you will follow. Discuss safety precautions that must be used and list them in the space below.. 7. 3. 8. 2. 9 1. 10. 4. 7. 1. 10. 3. 8. 2. 9. Goggles and aprons must be worn. Handle hot glassware carefully, using appropriate hot pads. Apply electrical safety rules: disconnect hot plate when not in use; prevent electrical equipment from coming in contact with water or wet surfaces. General lab safety and personal safety precautions are applicable.. 1. Place 4–5 ice cubes (less than 100 g) and about 50 mL of water in a 250 mL beaker. 2. Connect the graphing calculator (TI-84) to CBL 2™ using the link. 3. Insert the temperature probe into Channel 1. 4. Select the DataMate program from APPS for data collection. 5. Complete setup of the calculator program for data collection as instructed on the following pages. 6. Place the temperature probe in the ice-water mixture. 7. Place the beaker with the ice-water mixture, thermometer, and magnetic stirrer on a hot plate. 8. Ensure that the probe is not touching the sides or bottom of the beaker by suspending it in the ice-water mixture with a clamp and stand. 9. Turn on the hot plate and stirrer. Set the heat at the high setting and the stirrer at the medium setting. 10. Begin heating and start the data collection.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(35) CHANGES TE. Changes 11. When data collection is complete and the graph is displayed, analyze and discuss it with your lab group. 12. Data and graphs from the calculator may be transferred to a computer using an interface program such as TI-Connect™. The investigation report may be printed out then. OR Data may be transferred manually to the data table, and graphs may be constructed. Note If data are collected manually, record the temperature every 30 seconds until the temperature reaches approximately 100 °C and remains constant over several readings. The water should be visibly boiling at this time.. .

(36) CHANGES TE. Changes Data (for Manual Data Collection) Time Time Time Time (30 sec Temp (°C) (30 sec Temp (°C) (30 sec Temp (°C) (30 sec Temp (°C) intervals) intervals) intervals) intervals) 0. 2.0. 25. 52.5. 50. 101.0. 75. 1. 2.0. 26. 55.0. 51. 101.0. 76. 2. 2.0. 27. 60.0. 52. 77. 3. 2.0. 28. 64.0. 53. 78. 4. 2.0. 29. 67.5. 54. 79. 5. 2.5. 30. 70.0. 55. 80. 6. 3.0. 31. 73.5. 56. 81. 7. 3.0. 32. 76.5. 57. 82. 8. 4.0. 33. 80.0. 58. 83. 9. 5.0. 34. 83.0. 59. 84. 10. 7.0. 35. 85.0. 60. 85. 11. 8.5. 36. 87.0. 61. 86. 12. 9.5. 37. 88.0. 62. 87. 13. 12.0. 38. 89.0. 63. 88. 14. 14.0. 39. 92.0. 64. 89. 15. 17.0. 40. 90.0. 65. 90. 16. 20.0. 41. 94.0. 66. 91. 17. 23.5. 42. 96.0. 67. 92. 18. 26.5. 43. 98.0. 68. 93. 19. 28.5. 44. 99.5. 69. 94. 20. 32.0. 45. 100.5. 70. 95. 21. 34.0. 46. 101.5. 71. 96. 22. 37.5. 47. 101.0. 72. 97. 23. 44.5. 48. 101.0. 73. 98. 24. 49.5. 49. 101.0. 74. 99. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(37) CHANGES TE. Changes. Temperature in °C. Graph. Time Intervals (Every 30 Seconds from Start). .

(38) CHANGES TE. Changes Analysis and Conclusions 1. In your investigation, identify the independent and the dependent variables. The independent variable is the time interval, and the dependent variable is the temperature in Celsius. 2. How does the temperature of the ice-water mixture vary as it is continually heated? The temperature stayed constant (close to 0 °C) for about 5 minutes and then rose steadily until it reached about 100 °C. It remained at 100 °C for about 6 minutes until we stopped data collection and heating. 3. What do the different sections of the graph represent? The three sections in the graph represent melting ice, heating liquid, and boiling water. 4. From your graph, identify the melting temperature of ice and the boiling temperature of water. Melting temperature of ice = 0 °C Boiling temperature of water = 100 °C 5. Predict the shape of the graph if you cooled steam continually to change it to ice. Draw the predicted shape of the graph below. Identify the condensation temperature and the freezing temperature on the graph. The graph will be reversed in the cooling process of steam to water, then to solid.. Condensation (100 °C). Freezing (0 °C). Temperature in °C. cooling steam. steam to water. cooling water. water to ice. Time Intervals. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(39) CHANGES TE. Changes 6. Classify the following changes as endothermic or exothermic and give reasons for your classification. Change. Melting. Freezing. Boiling. Condensation. Endothermic or Exothermic. Reason. Endothermic. Heat is absorbed when ice melts and changes to a liquid.. Exothermic. Heat is released when water freezes to ice.. Endothermic. Heat is absorbed when water boils and changes to vapor.. Exothermic. Heat is released when water vapor condenses and changes to a liquid.. 7. Why do you think the temperature stayed constant as the ice melted into water? The energy absorbed was used to rearrange the particles of the solid into a more flexible arrangement of a liquid. Since the particles are not moving faster, there is no temperature change. After all the ice melted, the temperature increased, indicating that the water particles are moving faster. 8. Why do you think the temperature stayed constant as the water boiled? In the boiling phase, the energy is used to change the liquid particles to vapor particles. The energy is not used to increase the movement of the water particles, so there is no increase in temperature. 9. What is the difference between evaporation and boiling? Evaporation takes place on the surface of the liquid and happens at any temperature. For example, if you leave a bowl of water open to the air, it will evaporate. Boiling takes place when a substance is heated to a specific temperature. For example, water boils at 100 °C. Each liquid has a unique boiling temperature.. .

(40) CHANGES TE. Changes 10. Classify the following changes as physical or chemical and exothermic or endothermic. Give reasons for your classification. Change. Melting. Freezing. Boiling. Condensation. Evaporation. Physical or Chemical. Physical. Physical. Physical. Physical. Physical. Exothermic or Endothermic. Reason. Endothermic. No new substance is formed and the change is reversible. Heat is absorbed.. Exothermic. No new substance is formed and the change is reversible. Heat is released.. Endothermic. No new substance is formed and the change is reversible. Heat is absorbed.. Exothermic. No new substance is formed and the change is reversible. Heat is released.. Endothermic. No new substance is formed and the change is reversible. Heat is absorbed.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(41) CHANGES TE. Changes Notes: Phase Changes All phase changes are physical changes because the chemical makeup of the substance does not change and the substance can easily be recovered. The temperature remains constant during a phase change. The energy absorbed during a phase change such as melting, evaporation, or boiling is used to overcome the forces holding the particles together. In phase changes like freezing and condensation, energy is removed or released so that movement of the particles is slowed down and the particles align themselves to form a solid or liquid.. Heating Curve of a Solid to Vapor. heating vapor. Temperature in °C. boiling. melting. heating liquid. heating solid. Time Intervals. .

(42) CHANGES TE. Changes Application: Phase Changes Two students conduct phase change experiments for a certain chemical using a graphing calculator and probes. One student works on the heating curve of the solid while the other student works on the cooling curve of the liquid. Both students decide to take temperature readings in Celsius every minute for 15 minutes. The two sets of graphs obtained by the students are shown below. Study the graphs carefully and answer the questions below. A. B. C. P. Q. R. 1. What is the independent variable in the experiment? What is the dependent variable? The independent variable is the time interval of 1 minute. The dependent variable is the temperature in Celsius. 2. Which set of graphs represents the heating of the solid? Which set of graphs represents the cooling of the liquid? How do you know? Set A, B, C represents the cooling of a hot liquid because the temperature is decreasing. Set P, Q, R represents the heating of a solid because the temperature is increasing. 3. Color or mark the melting point and the freezing point on the respective graphs. What are the melting temperature and the freezing temperature of the substance? Melting point and freezing point are the same temperature, 44 °C.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(43) CHANGES TE. Changes Elaborate. Teacher Notes. Materials List For each station • A set of chemicals as described below • Test tubes • Test tube rack • Stirring rod Station 1 • Solid A • Liquid B • Plastic scoop Station 2 • Liquid C • Liquid D Station 3 • Solid E • Water in a plastic cup • Plastic scoop • Pipette Station 4 • Hot plate • Large beaker with water for hot bath • Liquid F • Small beaker • Water in a plastic cup • Test tube holder Station 5 • Liquid G • Liquid H. . Investigate: Changes Students perform several chemical investigations. Each investigation allows the opportunity to apply laboratory process skills as well as understanding of physical and chemical changes. Students will observe and analyze their observations carefully to determine the attributes of the change. Independent student inquiry is emphasized. The Elaborate section may also be used as a performance assessment. Learning Outcome • Observe several changes while adhering to proper laboratory procedures. • Determine if a change has occurred based on observations. • Classify the change as exothermic or endothermic and give logical reasons for classification. • Classify the change as physical or chemical and give logical reasons for classification. Advance Preparation Collect lab materials and equipment needed for this investigation. The suggested chemicals below may be substituted with other chemicals at the teacher’s discretion. Obtain the chemicals listed below and place them in individual containers with labels as shown. The containers may be dropper bottles or disposable pipettes for the liquids and sample jars for the solids. About 10 g of solid and 25 mL of liquid should be sufficient. Each student group will need a set of chemicals. Chemicals Sodium bicarbonate Vinegar Potassium iodide solution 0.1 M Lead nitrate solution 0.1 M Calcium chloride Soy wax (melted before the investigation and kept in hot water bath) Mineral oil Water. Labels Solid A Liquid B Liquid C Liquid D Solid E Liquid F (place in test tube) Liquid G Liquid H.

(44) CHANGES TE. Changes Place the soy wax in test tubes, one for each student group. These test tubes are labeled “Liquid F.” Heat the soy wax test tubes in a hot water bath to melt the wax. The liquid may be obtained by the student groups when they are ready to conduct that part of the investigation. Note: Soy wax is nontoxic and is washable with soap and hot water.. Activity 1. Allow students to read and discuss the information on the laboratory sheet. 2. Review laboratory safety with attention to chemical, heat, and electrical safety. 3. Ensure that all student groups have the necessary equipment and materials to conduct the investigation. 4. Allow students time to conduct the investigation, discuss, and complete the laboratory record sheet. 5. Monitor students and intervene only when necessary. 6. After students have completed the investigation and cleaned up, conduct a class discussion to review student understanding of the major concepts in the lesson. Accept all answers before guiding student reasoning, using probing questions as necessary.. Discussion Questions 1. Which investigations represent a chemical change? Which were physical changes? 1 and 2 were chemical changes. 3 and 4 were physical changes. There is no change in 5. 2. How do you know that 1 and 2 were chemical changes? Bubbles of gas were produced in the first investigation, and yellow precipitate was produced in the second. (Usage of proper learned vocabulary is stressed.). © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(45) CHANGES TE. Changes 3. What were the reasons for classification in 3, 4, and 5? In 3, there was no observable change other than the temperature change, which alone is not sufficient to classify it as a chemical change. In 4, the hot liquid changed to a solid and floated on the water. It may be freezing of the liquid rather than a chemical change. In 5, the two liquids did not mix; they remained separate layers, so there was no change. 4. Which investigations were exothermic? How do you know? 3 and 4 were exothermic because in both cases the water temperature increased. 5. Which investigations were endothermic? How do you know? 1 was endothermic because the temperature of the contents in the test tube dropped. Heat was absorbed by the chemical change/ reaction. 6. In which investigation was mass conserved? Mass is always conserved in a change. In all the investigations, the total mass before the change equals the total mass after the change. 7. In which investigation was energy conserved? Energy is always conserved in a change. In an exothermic process, heat given off by the change is absorbed by the surroundings. In an endothermic process, heat needed for the change is absorbed from the surroundings.. .

(46) CHANGES TE. Changes Elaborate. Student Sample Accurate student answers are shown. Actual answers may vary. Investigate: Changes Safety Conduct the following investigations with attention to chemical and laboratory safety. Assume that the chemicals used in the investigations are toxic and corrosive. List the safety precautions in the space provided. goggles; aprons; wash hands after lab; follow all lab rules; observe electrical safety, heat safety, and chemical safety rules Add one substance to another as directed in the table below. Observe carefully and record your observations. Classify the changes as physical or chemical and state your reasons for the classification. Be prepared to discuss your observations, analyses, and conclusions with the class. Investigation. Observation. Physical/Chemical How do you know?. Exothermic/Endothermic How do you know?. 1. Place about 2 mL of bubbles of gas Liquid B in a test tube. solid dissolves Add a very small amount of solution gets cold Solid A to Liquid B.. chemical change new gas product formed. endothermic temperature drop indicates that heat was absorbed by the reaction. 2. Place about 2 mL of Liquid C in a test tube. Add a few drops of Liquid D to Liquid C.. yellow precipitate clear solution on top no change in temperature. chemical change new yellow solid product formed. no observed change in energy. 3. Place about 2 mL of water in a test tube. Add a peasized scoop of Solid E to the water in the test tube.. no observed change (color, gas, or precipitate) solution gets hot. physical change no new product formed. exothermic temperature increases. 4. Fill a small beaker half-full with water. Obtain Liquid F from your instructor. (Caution: This liquid may be hot.) Carefully pour the hot Liquid F into the water in the beaker.. white solid formed floats on top of water hot Liquid F cools and the water warms up. physical change Liquid F freezes to a solid. exothermic hot liquid cools before it changes into a solid. 5. Place about 2 mL of Liquid G in a test tube. Add an equal amount of Liquid H to the test tube.. Liquid G and Liquid H do not mix. They form two layers.. no change no new product or change in properties of the materials. no observed change in energy. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

(47) CHANGES TE. Changes Analysis and Conclusions 1. In which investigation is mass conserved? Mass is always conserved in any change. Mass is conserved in all five investigations. 2. In which investigation would you expect to observe a reduction in mass? Why? Mass may appear to decrease in Investigation 1 because a gas product was released in the reaction. This gas was not trapped but was allowed to escape into the atmosphere. The final mass should be less than the initial mass.. .

(48) CHANGES TE. Changes Evaluate Key. A student’s experimental procedure and observations are diagramed below. Study diagrams A through F and answer the questions below. A. mass of empty test tube = 32.5 g. D. temperature of clear liquid in beaker = 25.1 °C 10.0 g of clear liquid is poured into the white powder.. C. B. white powder added. E. Gas bubbles were given off. temperature of liquid in test tube = 23.3 °C. mass of test tube with powder = 33.6 g. F. mass of test tube with liquid = 41.8 g. 1. If there was a change, was it a physical change or chemical change? Explain. This is a chemical change because a new gas product is produced when the liquid and solid are mixed. 2. Was the process endothermic or exothermic? Explain. This is an endothermic change because the temperature dropped from 25.1 °C to 23.3 °C. The heat needed for the reaction was absorbed from the liquid. 3. Was mass conserved in this process? Explain. Mass is always conserved in a chemical or physical change. Mass of reactants = mass of white powder + clear liquid = 1.1 g + 10.0 g = 11.1 g Mass of products = 41.8 g – 32.5 g = 9.3 g The gas product may account for this decrease in mass.. © 2011 TEXAS EDUCATION AGENCY. ALL RIGHTS RESERVED.. .

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