Students will learn about and discuss the behavior of a gas using examples of convection and an optional teacher-led demonstration. Students will then participation in a lab where they will investigate water currents by observing the results of mixing colored warm water with room temperature water. The lab will be followed by a discussion about the molecular activity of the water mixture.
By the end of this lab, students should be able to:
- Form an understanding of the effects of heating and cooling.
- Explain that warm air and liquids rise because they are less dense than cold air and liquids.
- Describe the molecular motion of gases and liquids, and how temperature impacts the motion.
This lab supports the students’ understanding of:
- States of Matter
- Molecular Motion
Teacher Preparation: 30 minutes
Lesson: 60 minutes
Materials (per group)
- Fish tank almost filled to capacity with water
- Food coloring
- Baby food jar
- 2 straws (or plastic eye droppers/pipettes)
- Hot glue (or clay)
- Hot water
- Always wear safety goggles when handling chemicals in the lab.
- Students should wash their hands thoroughly before leaving the lab.
- When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
- Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
- This topic can be introduced through a teacher-lead demonstration, An Uplifting Experience, found in the AACT Resource Library. However, if time constraints or limitation of materials will not allow for using the demonstration, the following videos and examples will also benefit student understanding of the topic.
- Before beginning the demonstration, engage the interest of students through a time lapse viewing of the Albuquerque International Balloon Fiesta.
- Conduct a discussion about objects that rise into the air and the possible reasons that allow for the objects to rise.
- Draw the attention back to the hot air balloons through a second video clip which shows the air being heated, allowing the balloon to rise.
- Guide student understanding to the idea that warm air rises and is lighter, or less dense, than the surrounding colder air. Also, explain that air molecules are being heated causing their movement to increase in speed and to spread out more.
- Introduce the term convection to students and relate it to why we and firefighters are instructed to crawl on the ground to escape hot smoke inhalation if caught in a fire. The hot smoke rises, and the cooler, breathable air is down near the ground.
- Complete the demonstration, An Uplifting Experience. Conclude that the movement of warmer air upwards and colder air downwards is called convection. Also inform students that this also applies to warm and cold water.
- Next, students will apply what they learned about air currents and convection to a lab experience about water temperature and currents.
- The lab is best managed with students placed in small groups of approximately 4 students per group.
- After the lab make students aware that ocean currents are examples of convection. Also, hot springs where the cold rain water falls is heated thermally by Earth’s mantle. The cold rain water sinks and the warm water rises.
- This lab lends itself to be used when studying properties of matter, specifically gases and liquids. It may also be used in a unit about weather.
- For the student lab the teacher should prepare the convection jar lid ahead of time:
- Punch two holes in a baby food jar lid and insert straws. Insert one to be as deep as the jar and place the other above the lid. Seal them with clay or hot glue.
- Note: When you fill the jar with colored water ensure that it is full to capacity including the capacity of the straw that is inside of the jar. Do this by filling the jar, then securing the lid; finally fill the straw to capacity with the warm water before submerging it into the aquarium (or other transparent container).
- As an extension option for the student lab you could create 3 different convection jars containing different colored water samples, at different temperatures. This would allow students to investigate if the temperature of the liquid affects the liquid to rise more, or rise faster.
- Below you can see images of anticipated results for this lab. On the left is the convection in action, after the jar has been added to the aquarium. On the right the convection process is near completion, as indicated by the color change in the jar.