1 of 16

Navigation

Slide A

Turn and Talk

What evidence did we use to conclude that the gas in the bubbles was not one of the three substances we started with (baking soda, citric acid, or water)?

What kind of gas do you think it could be? Feel free to brainstorm multiple gases.

Be prepared to share these with the whole class.

Turn and talk about the previous lesson. Display slide A. Say, With an elbow partner, discuss what evidence we collected that helped us know that the gas bubbles from the bath bomb were not one of the three substances we started with (baking soda, citric acid, or water). Then discuss what kind of gas you think it might be. Feel free to brainstorm multiple predictions.

Share ideas with the class. After a couple of minutes, have students share some possible gases it could be. Anticipated responses will be any gases that students already know. If students completed the Storms Unit, they are likely to mention some of the gases that make up the atmosphere, such as nitrogen, oxygen, and carbon dioxide.

Lead a short discussion to help students see that using properties to find out what kind of gas is coming from a bath bomb could be a good next step.

Say, We know that there is more than one type of gas in our world. If we want to figure out what gas is in those bubbles, we could try to identify it based on its properties and compare it to the properties of other gases in the world around us. But what exactly are some different properties of gases? That seems tricky to determine because gases are invisible. Let’s pause here and try to try to think of some related experiences with gases that might help us figure out some properties they have that we could use to tell them apart.

2 of 16

Related Phenomena

Slide B

Stop and Jot

Title a new page of your notebook “Gas-Related phenomena.”

Under it, list any experiences you’ve had with different kinds of gas(es) used in different systems where they made different things happen.

Scientists can identify different substances based on their properties.

If we want to figure out what gas is in those bubbles, we also could try to identify the gas based on its properties.

What are some different properties of substances that are gases at room temperature?

Consider related phenomena around gases. Display slide B. Ask students to title a new page in their notebook “Gas-Related Phenomena.” Tell them to list any experiences they have had with different kinds of gases. These can be gases that are used in different types of systems to make different things happen.

Then after brainstorming for a couple of minutes, ask students to share ideas. Student ideas may include:

gas in a balloon (helium),
the Goodyear Blimp that sometimes appears at sports events,
gas stoves to cook on,
gas in grills or fireplaces, or
the gas fizz in a soda.

After getting some of these examples, say, These are examples where different kinds of gases are used to make different things happen. Let’s talk more about how the gases used in these systems can make these things happen. Use the following example prompts to elicit student ideas about the properties of gases.

Adding properties to the Word Wall. Say, What you are describing is actually considered a property. Does anyone know what it is called? If students do not know the property of flammability, introduce the term now. Have a student write the word “flammability” on a sticky note and add it to the Word Wall as another example of a property. An example definition for flammability: how a substance interacts with fire. If density is not on the wall, write it on a sticky note too, and add it to the Word Wall as another example of a property with the definition: how much matter there is in a certain space.

If odor wasn’t added to the Word Wall in Lesson 3, students may suggest odor as a way to identify the gas because they may have smelled natural gas from a gas leak or they may remember that some bath bombs had an odor. Remind them that we think odor might be considered a property. Tell them that natural gas has an odor because another substance is mixed into it that has a rotten-egg-like odor to aid in the detection of gas leaks--the natural gas itself is actually odorless. Ask students if all bath bombs had an odor. Then ask students if they detected an odor when they combined the baking soda and citric acid. They should mention that they did not detect an odor when the baking soda and citric acid were combined, but they did detect an odor with most of the bath bombs.

Say, Let’s look at some of these properties of different gases and compare them.

3 of 16

Properties of Some Common Gases

Slide C

All data reported is for measurements at sea level elevation and at 15℃
Substances in rows A–I (row J is a mixture)		Approximate % of this gas in the air outside	Boiling point (in °C)	Density (g/L) measured at 0°C	Flammability Notes on how the gas interacts with flame
A	nitrogen	78%	-196	1.250	Will extinguish a flame.
B	oxygen	21%	-183	1.430	Will increase a flame or cause a glowing ember to burst into flame.
C	argon	~1%	-186	1.780	Will extinguish a flame.
D	carbon dioxide	~0.04%	N/A Changes straight from solid to gas with no liquid phase. This occurs at -78.4	1.960	Will extinguish a flame.
E	neon	~0.0018%	-246	0.900	Will extinguish a flame.
F	helium	~0.0005%*	-268	0.179	Will extinguish a flame.
G	methane (natural gas)	~0.0002%*	-161.5	0.714	Will increase a flame. Can create an explosion
H	hydrogen	0.0001%	-252	0.090�	Will increase a flame. Can create an explosion.
I	propane	<0.0001%	-42	2.000	Will increase a flame. Can create an explosion.
J	Air	N/A	N/A (mixture)	~1.160	Can maintain an open flame.

Distribute Some Common Gases to students. Display slide C. Give students 2–3 minutes to look over the list of gases and share their noticings and wonderings verbally with a partner.

After students have had time to share with their partner, lead a short discussion to bring out their ideas.✱

Brainstorm how we could test the gas from the bath bomb for these properties. Ask students for some suggestions for ways to trap the gas from a bath bomb so that we can test it for these properties. Also ask them for ways to compare the gas in the bath bomb to other gases in the table. Students will likely suggest bottles or bags based on their experience from Lesson 2.

Say, OK, let’s plan to trap some gas first and then check it for one of these properties. Let’s start with checking its flammability, and then we can look at density after that. One thing that scientists often do when testing the properties of an unknown substance is to compare it to the properties of some known substances. Such comparisons are called control conditions. This increases the reliability of the results for the unknown substance, since a comparison between the behavior of a known substance and an unknown substance can often reveal problems in the equipment you are using or in your experimental procedure. I have two gases we can use as controls for this comparison. I have some helium gas we can use and we can use air from the room. Let’s review safety guidelines for these flammability tests.✱

Review safety guidelines for this demonstration. You will need two volunteers to help. Have students put their goggles on and gather around the demonstration area.

Fill one flask with helium and one with room air.

4 of 16

Testing Known Gases for Flammability

Slide D

Turn and Talk

What do you predict will happen to a lit match when it is in placed inside a bottle filled with air from the room?

How about when the match is placed in a bottle filled with helium gas?

5 of 16

Testing an Unknown Gas for Flammability

Slide E

Turn and Talk

What do you predict will happen to a lit match when it is in placed inside a bottle filled with air from the bath bomb?

6 of 16

Eliminating Candidates

Slide F

Consider this question, “What gas(es) could be coming from the bath bomb?”

Use your handout to eliminate the gases that are no longer possible candidates. Cross each of these off.

What did you figure out from this investigation?

Show slide F. Say, Now that we have this result, we can use it to strike through all the gases that do not have that property on our list of candidates. Give students a few minutes to mark off gases from Some Common Gases. They should be eliminating air, oxygen, hydrogen, methane, and propane.

Introduce the idea of testing density. Say, OK, we tested the flammability of the bath bomb gas, but there was another property listed that we wanted to test. What was that other property? Students should say density.

Say, The last time you studied the density of gases was in the [material: wc.n]. In that unit, you learned that when a gas or liquid is more dense than the surrounding gas or liquid it sinks downward and when it is less dense than the surrounding gas or liquid it floats upward. Let’s look at helium’s reported density and make predictions about what helium would do if we released it from a container into the surroundings.

7 of 16

Testing a Known Gas for One Property

Slide G

Whole-Group Discussion

Look up the density of helium. Based on how its density compares to air, what do you predict it will do? Will it float upward or will it sink downward when released from a container?

Predict the behavior of helium. Display slide G. Discuss predictions as a class. Students should predict it will float upward. Say, Let’s test it.

Fill one flask with helium and one with room air.

Say, OK let’s get ready to release it and see if it floats upward or sinks downward. Are you ready? Wait about 10 seconds. Students are likely to raise a concern before you release the stopper, saying, How will we be able to tell which way it goes? It's invisible!

If students don’t object, then simply open the stopper on the flask. Wait about 10 seconds and then ask, Did the release gas travel upward like you predicted? It is at this point that you will definitely get some objections from students, saying, How were we supposed to be able to tell which way it went? It's invisible!

Suggest using its flammability as a way to test whether it is less dense or more dense than air. Say, Good point. We need a way to detect whether the helium gas traveled upward or downward. We already know something about its flammability though. So if we opened a bottle filled with the gas and held a match in front of it then opened and removed the cork, what should happen to the flame when the gas comes out of the bottle? Students should say it would go out.

8 of 16

Testing the Density of a Known Gas

Slide H

Turn and Talk

What do you predict will happen to the flame when the lid is removed from a flask filled with helium in the two different situations pictured below?

How could doing a similar test with the gas from a bath bomb tell us something about its density?

Share predictions. Show slide H. Give students a couple of minutes to discuss their ideas with a partner. Say, Let’s test this ourselves to see if our predictions are correct, and then we will use what we figured out and try to apply it to the gas from the bath bomb.

Test the flammability of the helium gas in each case.

Discuss these results. Ask students why the gas from the bottle extinguished the flames in one case but not the other. Students should say, It is because of its density, and that if the gas floats upward, it will only put out a flame above it, not below it, because it won’t fall downward out of the bottle.

Updating the Key Model Ideas poster. Co-construct a key idea about density that says something like, “Less dense gases (and liquids) float upward when surrounded by denser gases (and liquids); and denser gases (and liquids) sink downward when surrounded by less dense gases (and liquids).” Add this to the Key Model Ideas poster. Remember it is important to use the wording your class comes up with for this Key Model Idea whenever possible. Help students connect back to what they have seen in earlier units and what some groups may have seen in Lesson 4 with oil floating on water, if this is something they noticed, asking them what this shows about the density of oil compared to water. Students should say it shows that oil is less dense than water.

Introduce testing the bath bomb gas in a similar manner. Tell students that they will test the bath bomb gas in a similar manner tomorrow, but before they do you want them to make some predictions about what we could figure out about the gas from a bath bomb by doing a test similar to the one we just did, but with gas from a bath bomb trapped in a bottle or bag instead of helium gas.

Making predictive explanations. Pass out a copy of My Predictive Explanations for the Gas from a Bath Bomb. Ask students to use this handout to make two different if-then statements that will describe what they could learn from testing the density and flammability of the gas coming from the bath bomb.

9 of 16

Making Predictions

Slide I

Individual Predictions

If the gas from the bath bomb puts out a flame above it, that means it is __(more, less)__ dense

than the room air, which has a known density of __(a number and unit)__.

I know this because _______________________

____(connect to the related key model idea)__________

______________________________________.

If evidence supports this prediction, it tells me that the gas from a bath bomb could be ____________(list all possible gases)_____________.

10 of 16

Making Predictions

Slide J

Individual Predictions

If the gas from the bath bomb puts out a flame below it, that means it is __(more, less)__ dense

than the room air, which has a known value of __(a number and unit)__.

I know this because _______________________

____(connect to the related scientific principle )__________

______________________________________.

If evidence supports this prediction, it tells me that the gas from a bath bomb could be ____________(list all possible gases)_____________.

11 of 16

Slide K

Carrying Out Our Investigation

Work with Your Group

Fill a bottle about 1/10 full with water. Add 8 mini bath bombs to it. Cap it.
Light a match. Hold it 1 inch over the bottle as a partner removes the cap.
Keep it there for 2 seconds. Make note of whether the match goes out or not.
Extinguish the match and cap the bottle. Discard the match in a cup of water.

Light a candle in an aluminum bread pan.
Lean the edge of the bottle against the pan and remove the cap.
Gently squeeze the bottle to push the gas out of it. Make note of whether the candle in the pan goes out or not.

12 of 16

Progress Tracker

Slide L

Use your handout to eliminate the gases that are no longer possible candidates. Cross each of these off.

Then record what you figured out under the question “What gas(es) could be coming from the bath bomb?” in your Progress Tracker section.

What did you figure out from this investigation?

Question

Progress Tracker

What I figured out

What gas(es) could be coming from the bath bomb?

Updating the list of possible gases. Display slide L. Tell the class, Use the results of your investigation and your predictions to narrow down the substances the gas from the bath bomb could be. Cue students to look back through Some Common Gases and My Predictive Explanations for the Gas from a Bath Bomb and individually cross off candidates that they have now eliminated as they transfer their discoveries to their Progress Tracker.

Return student predictions. Pass back the student predictions they made on My Predictive Explanations for the Gas from a Bath Bomb. Have students attach their predictions to their notebook.

Divide the students into small groups. Arrange your students in groups of 3. Mix them in groups different from their lab group from the previous class. They will need:

their notebooks turned to their last entry in the Progress Tracker,
the data table from Some Common Gases,
their predictive explanations from My Predictive Explanations for the Gas from a Bath Bomb, and
the new handout, Discussion Protocol: Density and Flammability.

13 of 16

Arguing from Evidence

Slide M

Small-Group Discussion

Sit with your small group in a circle.

Review the protocol with your class before getting started.

Decide who will be the first to share in your group.

Follow the protocol until everyone has had a chance to share.

Set up the protocol. Display slide M and spend a few minutes as a whole class going over the protocol with students. Ensure that the anchor poster you made from Lesson 2 is clearly visible to all groups. Make sure they understand that everyone in the group will share their ideas in the form of making a claim about one gas that could be from the bath bomb or one gas it couldn’t be. All students will participate in giving feedback to their peers. Have students practice snapping their fingers and lightly tapping their feet. Reserve at least 9 minutes for students to participate in this activity. Set a timer so that students know when a new classmate should offer their claims.

Identifying overarching key model ideas to call out in our argument. Use the Key Model Ideas poster, and work together with the class to determine if there is one main key idea they can use in a written argument that identifies the remaining possible gases that could come from a bath bomb. Use the dialog below as an example to guide your discussion.

14 of 16

Arguing from Evidence

Slide N

Our question: What gas(es) could be produced by a bath bomb?

Your written argument should provide a claim to answer this question.

You should use all relevant evidence and reasoning (using scientific principles and ideas based on science) to support your claim. Look through your science notebook for these.

You should use our anchor chart to remind you of what is important to include.

Review instructions for the task. Remind the class that the ideas on the Anchor Chart can be used to build a strong argument. Go over each part of the poster, reminding students about the important parts of a strong argument. Display the Anchor Chart and slide N. This slide has the question they should answer: “What gas(es) could be produced by a bath bomb?” Say, Your written argument should answer this question. You should use evidence and key model ideas to support your claim. Use this anchor poster to remind you of what is important.

Give time for students to individually construct their arguments. Tell students where you want them to write their arguments, depending on how you want to gather their responses. If you want them to record their ideas in their notebooks, have them use a clean page and mark it so it is easy for you to find. Tell students that you will use this task as an assessment, so they should do their best work.

Encourage students by reminding them that they have had multiple chances to practice these arguments in small teams and with the whole class. Now it is time for them to write their arguments individually and “show off” what they have learned. Tell them that they can use the posters around the room, their notebooks, the data table, and any other material from the lessons as a resource to write their argument.✱

15 of 16

Navigation

Slide O

Turn and Talk

How is it possible that we have a new substance that was not there before?

You found that mixing baking soda, citric acid, and water produced the gas bubbles from the bath bomb. What do you think is going on with the particles of these ingredients to make the gas?

We know some possible candidate substances for the gas bubbles produced from bath bombs. We also know that this gas is a different substance from the substances that make up a bath bomb.

Display slide O. Say, Wow, we have figured out some ways to identify substances using properties. This has helped us narrow down to three possible substances that could be produced from a bath bomb placed in water. We also know that the substance in the gas isn’t one of the ones we started with, even though it came from the matter that made up the original substances. Without additional property data, this seems as far as we can go in figuring out what substance the gas is. It seems like we might need to take a different approach to investigating this process further, particularly if we want to figure out what is going on at the particle level that could explain how this is possible. But, before we continue our explorations of the bath bomb, I don’t want us to forget that we didn’t just want to explain what is happening in a bath bomb. We also have all these ideas on our related phenomena poster we wanted to be able to explain too. In our next class, let’s try and use what we have figured out so far to see if it can help us explain what is going on in a different phenomenon.

Share with students that during the next class period, they will have a chance to analyze some data from an investigation of a different related phenomenon and they will use this analysis to write multiple arguments about what is happening to the matter in the system.

16 of 16

Slide P

Carrying Out Our Investigation - Alternate

Work with Your Group

Add a teaspoon of citric acid and two teaspoons of baking soda to a quart size freezer bag. Fill a 15 mL centrifuge tube with water. Slide the tube into the bag without tipping it over and seal the bag. Tip the tube over to mix the substances.
Wait 30 seconds until the bag inflates.
Light a match. Hold it 1 inch over the bag as a partner opens the top of the bag. Keep it there for 2 seconds. Make note of whether the match goes out or not.
Seal the bag back up and wait for the bag to inflate or make a new bag (steps 1–3).
Light a candle in an aluminum bread pan.
Lean the edge of the gas filled bag against the pan and open the end. Gently squeeze the bag to push the gas out of it. Make note of whether the candle in the pan goes out or not.