The Arizona STEM Acceleration Project

Reaction in a Bag! - Day 1

Reaction in a Bag!

Day 1

An 8th Grade STEM Lesson

Katherine Otwell

June 2023

AZ Standards

AZ Science Standard

8.P1U1.1

Develop and use a model to demonstrate that atoms and molecules can be combined or rearranged in chemical reactions to form new compounds with the total number of each type of atom

conserved.

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Az Science Standard

8.P1U1.2

Obtain and evaluate information regarding how scientists identify substances based on unique physical and chemical properties.

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STEM Standards

Obtain, evaluate, and communicate information:

1. That all of matter is comprised of atoms, there are over 100 kinds of atoms, and each “kind” is an element differentiated by its properties.

2. About the characteristic physical and chemical properties of pure substances before and after they react.

3. Investigate and identify patterns when atoms rearrange in a chemical reaction to form new compounds

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Develop and use an (atomic) model:

3. That demonstrate when a chemical reaction occurs, the atoms that make up molecules of reactants rearrange and form new molecules, and that these products are equal to the number and types of atoms that make up the reactants.

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Engineering Standards

Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

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Develop and/or use a model to predict and/or describe phenomena.

Background:

The three substances used in this demonstration are all common chemicals. Sodium bicarbonate, or baking soda, is used as a food additive in baking. It is also used as a natural deodorant to remove odor-causing chemicals in refrigerators and in carpets. Calcium chloride (“road salt”) is a salt-like compound that is used as a de-icer for sidewalks and roads. Phenol red is a naturally occurring dye that is used as an indicator—it changes color under different conditions. Note: Phenol red is a solution of the dye dissolved in water. Water should be considered as a fourth substance (variable) in the overall reaction, and its effect should also be examined.

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When three substances—solid calcium chloride, solid sodium bicarbonate, and a solution of phenol red in water—are mixed, a series of changes is observed. These observations include temperature changes, color changes, and changes in state. How can we learn more about the individual interactions responsible for each observation? Imagine that each substance in the mixture represents a variable. By changing only one variable at a time, it should be possible to determine the contribution of each substance to the changes observed for the overall reaction.

Safety Precautions

Demonstration Overview

Calcium chloride is slightly toxic by ingestion. Phenol red is a dye solution and will stain skin and clothing. Be careful to mix the chemicals in the amounts called for in the procedure. Adding too much of the solids may result in excessive release of gases that are difficult to contain and may cause chemical splashing. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please review current Material Safety Data Sheets for additional safety, handling, and disposal information.

Day 1 - The purpose of this inquiry-based demonstration is to have students make observations about the changes that occur when several substances are mixed.

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Day 2 - The students are then challenged to design controlled experiments to identify the substances responsible for the observed changes.

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*This is a two day lab - The demonstration is day 1. During day 2 students will investigate one of the questions they created at the end of day 1.

Notes for Teachers

Description: This video shows a chemical reaction of sodium bicarbonate (baking soda), calcium chloride (road salt), and an indicator phenol red. The chemicals react to form calcium carbonate, sodium chloride, and carbon dioxide gas. This changes the pH inside the bag resulting in a color change in the phenol red. As much air as possible should be removed from the bag as possible to show the production of the gas. This could be used as an example of chemical reaction that releases energy (exothermic). Since the bag is sealed it could be massed before and after to show the conservation of mass (atoms).

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Notes for Teachers

There are so many ways to tweek this lesson to meet the needs of your students.

• I would advise the demonstration is a separate day from the student led activity. That is my day 2.
• This demonstration can be done in groups as opposed to a teacher demonstration.
• If you review the “Tips” pages you will see adjustments you can make to the lab so that you can study the law of conservation of mass using exact measurements. I don’t because I want my students to make those measurements in a separate lab. This lab focuses on chemical reactions.

• The day 2 activity allows students to choose what chemicals they believe influences the outcome of the reaction done on day 1 when the group creates the 4 questions at the end of day 1. Please be sure you check their questions before students leave or check them before they begin day 2.
• Bozeman Science on YouTube is a great resource for you or your students.
• You may not need or want to remediate or enrich until after day 2 because the students really can’t be wrong on what they observe and decide to investigate on day 1.
• Students should understand what is in the Bozeman Science video on NGSS PS1A - Structure and Properties of Matter prior to this lesson, but it definitely reinforces that standard during both day 1 and day 2 lessons.

Notes for Teachers

Materials for the demonstration:

• 1 tablespoon of calcium chloride
• 1 teaspoon of sodium bicarbonate
• 10 mL of phenol red indicator solution (.02%)
• 1 ziploc baggie
• pipet to dispense phenol red
• tablespoon
• teaspoon

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• Laser thermometer, if possible.
• Copy of Table A - pdf link

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Class work:

• Dry erase boards or butcher paper for each group. If using a dry erase board have students take a picture. They will revise this drawing at a later time.
• Markers / colored pencils to draw model.

Tips:

• If teaspoon and tablespoon measuring spoons are not available, plastic teaspoons will work well. Use three of these teaspoon-size amounts of calcium chloride in place of one tablespoon, as called for in the procedure. Plastic Solo™ cups can also be used instead of beakers to hold the reagents. If desired, the controlled experiments can be carried out in these plastic cups as well, although the temperature changes are easier to observe (feel) when the reactions are carried out in plastic bags.
• In order to maintain the introductory, “inquiry-based” quality of this demonstration, the procedure is qualitative rather than quantitative. Thus, the amounts of reagents are not massed and temperatures are not measured. The procedure can be adapted to a quantitative level, if desired, by massing the amounts of reagents used. An interesting extension in this case would be to find the ratio of reactants that produces the largest temperature change coupled with the greatest amount of gas. (These two trends may be at odds with one another.)

Tips:

• It is not necessary to understand the precise chemical events that take place in this reaction in order to appreciate the essence of this activity, which is the nature of scientific inquiry. This activity provides a great introduction to develop the theme that the heart of science involves asking questions.
• The first part of this demonstration is a fun and easy way to introduce students to the study of chemistry—students can actually hold an experiment in their hands to see and feel what chemistry is all about. Students also learn to (1) observe phenomena and ask questions; (2) design a scientific study to answer their questions; (3) collect data; and (4) analyze data.

Tips:

• The following information may be of interest to those students who are curious about what occurs. Do not present this information to the students prior to the activity! Calcium chloride produces heat (exothermic) when it dissolves in water, while sodium bicarbonate absorbs heat (endothermic) as it dissolves. Calcium chloride, baking soda, and water combine to produce carbon dioxide gas. Phenol red is an acid–base indicator that changes color in the presence of acids and bases. Sodium bicarbonate is a base, so it maintains the bright red (basic) color of phenol red at first. As sodium bicarbonate reacts with calcium chloride in water, acidic substances are produced and the color of the phenol red indicator changes from the basic form to its yellow, acidic form. Carbon dioxide is one of the acids produced—it dissolves in water and reacts to form carbonic acid, H2CO3, which makes the water acidic. As carbon dioxide is allowed to escape, the water may turn slightly orange or pink again.

Tips:

• The products of the reaction include sodium chloride (NaCl), table salt; calcium carbonate (CaCO3), the main component of chalk; and carbon dioxide (CO2), the metabolic “waste” gas exhaled during respiration.
• The events that take place in the zipper-lock bag are part of a dynamic and complex reaction. Intermediate products may be formed and then react further to produce the final composition of the product mixture. The following equation provides a snapshot of the initial and final composition and does not show all of the possible intermediate products.

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CaCl2(aq) + 2NaHCO3(aq) + phenol red (basic form) → CaCO3(s) + 2NaCl(aq) + H2O (aq) + CO2(g) + phenol red (acidic form)

Tips:

• This demonstration does not require any knowledge of chemistry content beyond the scientific method. Teachers who have already covered physical and chemical changes, however, may find it natural to discuss these additional concepts as well. Which observations are due to physical changes and which to chemical changes? Challenge students to propose additional experiments to prove that dissolving the individual solids in water represent physical changes, but that reacting the two solids together in water produces a chemical change.

Objective(s):

Today

• Students will make qualitative observations about the physical properties of each substance prior to demonstration.
• Students will make qualitative observations about the chemical properties after the demonstration.
• Students will ask questions about what they observed.
• Students will develop a model of what was observed during the demonstration.

Agenda (1 - 55 minute class period)

DAY 1 -

1. Teacher will complete a demonstration.
2. Each student will make qualitative observations on handout Data Table A.
3. Each group will discuss and write down 4 questions in Table A that could be investigated to determine the individual interactions that are responsible for the observed changes.

4. Each group will draw a model (can be pictures and words) that explains what occurred during the demonstration with the chemicals. (Students should take a pic if completed on white board.)

Driving Question

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How can we determine a chemical change has taken place?

What distinguishes a chemical change from a physical change?

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Hands-on Activity Instructions

• Students should be in groups of 4
• Each group should have a white board and marker or butcher paper.

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Procedure

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Part A: The Overall Reaction

1. Make copies and distribute Data Table A to each student.

2.Have students observe and describe the appearance of calcium chloride, sodium bicarbonate, and phenol red solution, then record the observations in Data Table A prior to mixing. You can walk around the room, or place small samples at each group.

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3.Obtain both a teaspoon and tablespoon scoop to dispense the sodium bicarbonate and calcium chloride, respectively.

4. Add one tablespoon of calcium chloride (a) to one corner of the baggie.

5. Add one teaspoon of sodium bicarbonate (b) tto another corner of the baggie. Do NOT allow them to mix.

6. Use the pipet and fill it three times with phenol red (c). Do NOT let it mix with the 2 other chemicals. In the video it shows the 2 dry chemicals in the baggie and the phenol red is in a paper cup. You can do it that way also.

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Hands-on Activity Instructions

7. Close the baggie without mixing then mix it all together once closed, and then set it down. MAKE SURE YOU HAVE AS MUCH AIR OUT AS POSSIBLE.

8. If you have a laser thermometer, you can check the temperature several times as the reaction continues.

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9. Choose to have a few students come up to touch the baggie or walk around classroom.

10. Have students observe and describe what they’ve witnessed in the demonstration.

11. Write observations in Table A.

Note: If the bag gets too tight due to the buildup of gas pressure, open the bag and then reseal it. Do NOT open the bag near your face or the face of any student!

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Hands-on Activity Instructions

11. Post this question on the board: What questions arise concerning the changes that were observed during the reaction in the bag? (This is the last box at the bottom of Table A).

Instruct each student group to consider at least four questions at the bottom of Table A that could be investigated to determine the individual interactions that are responsible for the observed changes. For example, is water or a liquid necessary for the reaction to occur? Have students write their questions down in the spaces provided in Data Table A.

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Assessment

Students are able to write 4 questions that can be investigated based on what they saw in today’s demonstration.

Students have a model (that may be modified on day 2) that explained what occurred during this demonstration. Draw either on dry erase board or butcher paper. You can also have each student draw on the back of Table A, then on day 2 they can create a group model and modify it according to day two’s activity.

There are questions at the end of day 2 over both lessons that could also be used as an assessment.

Differentiation

The video can be used to remediate what students have witnessed during the demonstration.

You don’t have to show the entire video, but it covers chemical reactions from elementary to high school.

I would have students do a KWL after the demonstration in this lesson, and the “W” would be what they didn’t understand from the driving question at the beginning of this lesson. After this video the students should be able to answer the W question and state more facts they learned from the video.

Remediation

This video can also review or reinforce the properties of matter discussed in this lesson.

The video can be used to enrich what students have witnessed during the demonstration. It discusses at the high school level about reaction rates and balancing equations. Students can go to http://colorado.phet.edu and use the simulation that he shows in the video to investigate further.

Again, I would use a KWL to have students summarize what they have learned, what they want to learn and what they learned on these high school level standards.

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Extension/Enrichment

Misconceptions (Fine Tuning Day 1 & Day 2 Lesson)

The video can be used to fine tune day 1 and day 2 and/or an extension. The activity to go along with the video would depend on what your focus would be.

The “misconceptions” section would be really good after you discuss Law of Conservation of Matter/Mass, as well as, Arizona’s standard 8.4PU1.3.

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Misconceptions & Fine Tuning