Cloud in a Bottle
Lesson 12 of 14
Objective: SWBAT determine conditions necessary for cloud formation and model the relationship between pressure and cloud formation and the relationship between temperature and cloud formation.
The goal of this lesson is for students to be able to explain how high and low pressure systems affect weather phenomena such as clouds by applying what they've learned about gas behaviors. The first part of the lesson includes a demonstration followed by a student investigation.
To set up for the first demonstration, have hot plates in front of the class along with an Erlenmeyer flask, balloons, a bath of ice water, a beaker of 20 mL of tap water.
- Erlenmeyer flask
- hot plate
- beaker of water (20 ml)
- 2 L plastic soda bottle (one per group)
- warm tap water
- safety matches
- isopropyl alcohol
Common Misconceptions (from Laura Henriques, California State University, Long Beach, Science Education Department)
Rather than thinking . . . .
Many students think . . .
Cloud formation is dependent upon the amount of water evaporating and condensing. Water molecules are continually changing state between solid, liquid and gas. When more molecules evaporate into the atmosphere than condense on earth, clouds can form.
The reason clouds form is because cold air doesn’t hold as much water as warm air (Fraser, 2000).
Possible source of misconception: lots of books (and therefore lots of teachers) say this! This is actually a more useful explanation as it has in it the concept of air parcels and their conservation of mass.
Clouds are created when water vapor condenses onto dust or other particles in the air. The water vapor is in the atmosphere as a result of evaporation of water from the surface of the earth, and from respiration of plants and animals.
Airborne particles affect cloud formation.
Clouds go to the sea and get filled with water. NOTE: that students with this idea view the water cycle only in terms of liquid water - there is no phase change required for this model. The next stage is for students to view the water cycle in terms of water boiling - for students in this stage the only way water becomes a gas is through boiling (i.e., no evaporation).
A visible cloud is primarily tiny water droplets and/or tiny ice crystals; it is not water vapor.
Clouds (and rain) are made by God (Piaget as cited in Bar, 1989 & Dove, 1998).
Clouds come from somewhere above the sky.
Empty clouds are refilled by the sea (water stays as a liquid through the entire process) (Bar, 1989; Philips, 1991).
Clouds are formed by boiling - vapors from kettles or the sun boiling the sea (Philips, 1991).
Clouds are made of cold, heat, fog, snow or night.
Clouds are mostly smoke, made of cotton or wool, or they are bags of water (Philips, 1991).
Clouds are sponges that hold water.
Clouds are water vapor.
Clouds are dust particles.
Possible source of misconception: cloud formation is often demonstrated with a tea kettle; evaporation is a liquid turning to a gas — just like boiling; when clouds and water vapor demonstrations are done in school students see the condensed water as a cloud but think they are seeing water vapor (which is actually invisible); clouds of cotton or other substances might result from our descriptions of clouds or art projects.
Clouds are necessary but not sufficient predictors of rain. The presence of clouds does not mean it will rain.
Clouds and rain are independent (Bar, 1989).
Clouds foretell rain (Bar, 1989).
As students into the room have the following prompt written on the board and ask them to take out their science journal and spend a few minutes younger ideas.
How do you think temperature, pressure or changes in volume are involved in cloud formation?
Give students time to think about their responses and records there answers in there journal. After 3-4 minutes, have students turn and talk to their neighbors and formulate a response that represents the shared thinking of the people at their table. Bring the entire class back together and have each table group share out there collective ideas.
During their sharing, ask students to tell you their ideas about how water vapor gets into the atmosphere and eventually forms clouds. Now is not the time to correct any of their answers, Just listen to their ideas.
To begin the demonstration, add 5 mL of tap water to the Erlenmeyer flask then place the balloon over the opening to seal the flask then place it on a hot plate. Heat the water, but do not let it all boil away.
Carefully remove the flask from the hot plate and ask students to share what they observe. Have students explain to you why the balloon inflates by drawing on their prior learning from previous labs and investigations.
Repeat the procedure with a second Erlenmeyer flask but this time do not stretch the balloon over the opening until after you remove it from the hot plate. Place the flask into the ice water bath. If done correctly the balloon should be inverted into the flask. Again ask students what they think is happening. Relate this back to previous lessons on air pressure.
There are four parts to this lab. Start by reviewing Gay-Lussac's law and the relationship between pressure and temperature at a constant volume and how clouds from. I address both of these in previous lessons.
If you are using the temperature strips, like those you find for aquariums, be sure that students can easily read them. Using clear, straight walled 2L bottles versus colored bottles will help.
Part four can be optional. It involves using a tiny amount of rubbing alcohol in place of the water. I recommend doing this as a demonstration as rubbing alcohol is flammable. If you have access to water bottle rocket device and pump or other similar apparatus, you can create a really dense cloud.
The reason the rubbing alcohol forms a more visible cloud is because alcohol evaporates more quickly than water. Alcohol molecules have weaker bonds than water molecules, so they let go of each other more easily. Since there are more evaporated alcohol molecules in the bottle, there are also more molecules able to condense. This is why you can see the alcohol cloud more clearly than the water cloud. - There's a demonstration, and instructions on Steve Spangler Science.
Follow up Questions:
- What did you observe inside the bottle when you squeezed and released the bottle?
- What gas law was operating during this experiment? Explain.
- If pressure decreases and volume increases when the bottle is released, what do you think happens to temperature? What evidence do you have?
- What happened when you used a dry bottle?
- What did you observe when you added water to the bottle?
- Low-pressure areas are the result of air rising into the atmosphere from Earth’s surface. Explain how this might result in cloud formation over a low-pressure area.
- High-pressure areas are the result of air falling from high altitudes and expanding. Explain how this might result in clear skies over a high-pressure area.
- What did you learn about cloud formation from today’s activity?
Below are images from a student completed lab.
In the video below students reflect on what they learned as a result of this investigation.
After you have your students clean up, engage them in the following questions. Giving an “answer” is never sufficient – they must explain their thinking:
With regards to the cloud in a bottle:
- What variables did you change when you pumped the air out of the bottle?
- What caused the cloud to form?
- Do you think the water vapor in the air in the room had any effect on the cloud formation?
With regards to Earth's Atmosphere:
- Is the air in our atmosphere in a container? Explain.
- What are the first steps in the formation of clouds? (Evaporation of water, followed by decreases in pressure and temperature.)
- Why does water vapor rise?
- What happens to the temperature and pressure of the water vapor as it rises?