In this demonstration, water is boiled in a flask, and a balloon is placed over the opening. As the flask cools, steam condenses, creating a partial vacuum that causes atmospheric pressure to push the balloon into the flask until it fills the interior.

1. Add about 10 mL of water to a 250-mL borosilicate Erlenmeyer flask.
2. Heat the flask on a hot plate or over a Bunsen burner until the water boils and steam rises.
3. Remove the flask from the heat and quickly stretch a balloon over the flask opening.
4. Cool the flask under running cold water or in an ice bath.
5. Watch as the balloon collapses and gets pushed inside the flask.

Similar concept: Balloon in a Bottle - Sick Science!:

📄 Balloon in the Flask - Flinn Scientific: https://www.flinnsci.com/api/library/Download/e2dfff9fc2324f51889429583a51ac63?srsltid=AfmBOory9enzier6TnB_y-Bn4jaZOAnmPEG1yWe25xmKV4hNn_8QZIna

• Put a hole in the flask and suck to 'blow up' the balloon.

• Take care when handling hot glass.
• Inspect flask for cracks or chips before heating.
• Only use borosilicate glass to avoid breakage.
• Be careful with steam and hot water to prevent burns.

• Why does the balloon get pushed into the flask instead of being “sucked” in? (It is pushed in by greater atmospheric pressure outside compared to the lower pressure inside.)
• What role does condensation of steam play in this experiment? (It reduces the internal pressure by creating a partial vacuum.)
• How is this similar to the Crush the Can demonstration? (Both rely on pressure differences caused by cooling steam inside a closed container.)
• What real-world examples show the effects of atmospheric pressure? (Vacuum-sealed food containers, suction cups, or collapsing oil drums.)