Misconceptions
1. Gas has no mass
- How to overcome this:
- First, ask the students what they think happens to the mass of the water that is now gas as it is being evaporated
- Physical demonstrations using very sensitive scales are important for teaching this specific concept
- Activity/Lesson Ideas:
- Place dry ice in a plastic bag and weigh it. Allow it to sublimate over a few hours/overnight. The bag will expand and the mass will be the same afterwards.
2. The space between gas molecules is filled with more atoms
- How to overcome this:
- Sinceatoms are too small to see, the demonstration can be done with simple drawings
- Be sure to state that gas molecules would not be able to move around (as is their property) if there were other atoms inbetween them
- Activity/Lesson Ideas:
- Drawing showing the space and movement of gas molecules as opposed to a drawing with other atoms filling the space
- Better yet, any YouTube video showing gas atom movement
Figure F.3 - Methane molecules
3. Attractive forces keep gas molecules together, repulsive forces keep them apart from the container
- How to overcome this:
- It’s hard not to think of attractive/repulsive forces when thinking about atoms in chemistry – address this!
- Come back to the Kinetic Molecular Theory which states that there are no such forces with in the gas state
- Activity/Lesson Ideas:
- Challenge the students with questions – “why do gas molecules diffuse?”, “how could gaseous mixtures exist?”
- The answers to all are that they are not attracted or repelled by one another but they follow diffusion
4. The pressure will decrease as volume decreases
- How to overcome this:
- Students generally have a hard time with the relationship between variables so it is important to have physical demonstrations for explaining the gas laws
- Activity/Lesson Ideas:
- Have the students push the desks in and walk around for 30 secs trying not to bump into one another. Divide the room in half and have the students attempt to avoid contact with only one half of the room. Follow with a debrief on the level of difficulty for each task. Relate this to Boyle’s law.
5. There is a lot of oxygen
- How to overcome this:
- It seems like there is a lot of air but compared to the composition of Earth, there is barely any air that humans use to breathe (O2 – 21%)
- Diagrams or charts can be used to make comparisons and to illustrate the point
- Activity/Lesson Ideas:
- Show diagrams of the Earth’s air components or of all the layers of the Earth (including the atmosphere) to show how very little of the atmosphere actually contains oxygen
- Compare to water and how less than 1% of water on Earth is drinkable
6. Climate Change and Loss of Ozone Layer are the Same Thing
- How to overcome this:
- Carbon dioxide emissions mostly contribute to climate change
- Chlorofluorocarbons (CFCs) contribute to ozone layer depletion and very little to climate change
- Activity/Lesson Ideas:
- Have the students conduct a case study on both issues to compare and contrast them
Figure F.5 - Boyle's law cartoon
Figure F.7 - Climate change vs. global warming
Figure F.4 - Gas molecules
Figure F.6 - Relative composition of air