Comparing Evaporation Rates

This demonstration shows how different liquids evaporate at different rates by measuring their temperature changes during evaporation. Students connect differences in evaporation rates to molecular structure and intermolecular forces using molecular models.

1. Set up a temperature sensor connected to a data collection device.
2. Place a small amount of the first liquid (e.g., water) on the sensor and record the temperature change as it evaporates.
3. Repeat the test with other liquids (e.g., ethanol, acetone, or isopropyl alcohol).
4. Compare the rate and extent of cooling for each liquid.
5. Use molecular model sets to build structures of the tested liquids.
6. Discuss how hydrogen bonding and molecular size influence evaporation rates.

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📄 Evaporative Cooling - PASCO: https://www.pasco.com/resources/lab-experiments/603?srsltid=AfmBOor3X1mRz5qCG4PEqijMf4lMTA8WfcJ94GkcIW6wjPfwAYfME3o5

• Use regular thermometers rather than temperature probes.
• Test additional compounds such as hexane or glycerol.
• Compare evaporation rates under different airflow conditions (fan vs. still air).

• Wear safety glasses.
• Perform in a well ventilated area.
• Do not ingest or inhale vapors from volatile liquids.
• Keep all alcohols and acetone away from open flames or heat sources.
• Wash hands after handling chemicals.

• Which liquid evaporated the fastest? (Likely acetone or alcohol, due to weaker intermolecular forces.)
• Why does water evaporate more slowly than alcohols? (Because water molecules form strong hydrogen bonds that require more energy to break.)
• How do molecular structures relate to evaporation rates? (More hydrogen bonding and stronger attractions slow evaporation.)
• How does this demonstration connect to sweating and cooling in living systems? (Evaporation removes heat, helping regulate temperature.)