Smelly Balloons (Athena Meltzer)

Author

Athena Meltzer

Principle(s) Illustrated

• Like the cell membrane, a balloon also is semi-permeable and allows molecules that are small enough to leave but keeps larger molecules from moving past the membrane. In this case the molecules of the extract are small enough to escape the balloon so we smell the extract but the molecules of the liquid that makes up the majority of the extract (water, alcohol) are too large and thus cannot escape the balloon (or enter it if the balloon is put under running water).

• The concept of diffusion is also illustrated here, as the air will gradually leak out of the tied balloon because the air inside the balloon is under higher pressure and will gradually diffuse into lower air pressure surrounding it.

Standards

• NGSS Science & engineering standards

  • Developing and Using Models

  • Planning and Carrying Out Investigations

  • Obtaining, Evaluating, and Communicating Information

• NGSS Cross-cutting concept standards:

  • Scale, Proportion, and Quantity

    • Phenomena that can be observed at one scale may not be observable at another scale. (MS-LS1-1)

  • Systems and System Models

    • § Systems may interact with other systems; they may have sub-systems and be a part of larger complex systems. (MS-LS1-3)

• NGSS Disciplinary core idea standards

  • LS1.A: Structure and Function

  • All living things are made up of cells, which is the smallest unit that can be said to be alive

    • cell membrane forms the boundary that controls what enters and leaves the cell. (MS-LS1-2)

  • Substances are made from different types of atoms, which combine with one another in various ways. Atoms form molecules that range in size from two to thousands of atoms. (MS-PS1-1)

    • Gases and liquids are made of molecules or inert atoms that are moving about relative to each other. (MS-PS1-4

Questioning Script

Prior knowledge & experience:

They know that all living things are made up of cells.

They may also understand the concept of diffusion and that molecules move from an area of higher concentration to lower concentration (from experience with spray air fresheners or perfume)

Students will also be familiar with the fact that a balloon filled with air will slowly deflate, although they most likely will not understand it is due to the fact that the pressure inside the balloon is greater than the surrounding air.

Root question:

Prediction: What do you think is going to happen when the liquid is poured inside the balloon?

Question: Why can we smell the scent molecules (why are they able to escape the balloon?), but the liquid molecules cannot enter or escape?

If the balloon were a cell, which structure of a cell would the balloon represent?

Target response:

The balloon represents the cell membrane. The cell membrane is semi-permeable and because the scent molecules are small enough they can escape the balloon. However, the molecules of liquid are too large and cannot enter or escape the balloon.

Common Misconceptions:

That some molecules are larger than others. Students have difficulty conceptualizing the just how small molecules are.

Worksheets:

Worksheet: Smelly Balloons Lab

• • • PS1.A: Structure and Properties of Matter