Salt and Sugar on the Sidewalk

Salt, sugar, limestone, and plastic particles affect the pattern of evaporation on a sidewalk. 

Possible Guiding, Compelling and/or Anchoring Questions

• What forces are involved? Why is the water around the particles evaporating at a different rate?
• Why did the phenomenon occur with some particles but not the others?

Classroom Suggestions

• Compare which of the substances dissolve in water or other liquids (like dissolves like) and tie to chemical bond types. 
• Compare sodium chloride and calcium chloride’s attraction for water and link to road deicers. 
• Topics to extend the discussion: How do salt and sugar affect whether foods lose moisture and get stale? (Note: stale crackers are not dry enough; stale bread is too dry.)
• Evaporation rates in salt lakes decrease during drought periods (per surface area) as previous evaporation concentrates the dissolved salt.

Related Resources

• American Chemical Society: Temperature and Energy: Explains the meaning of temperature and the energy exchanges in evaporation.
• American Chemical Society: The Energy of Evaporation: Background on forces and an investigation to compare the energy of evaporation of three liquids. 
• American Chemical Society: Lesson 1.3 Dissolving and Back Again: Detailed lesson plan for 5th grade that includes links to animations of salt dissolving and forming crystals as water evaporates.
• Chemistry LibreTexts: 9.1: Three Views of Chemical Bonding: Explains three models that are used to predict bonding and how charges are involved in each.
• National Weather Service: Heat Information Page: Shows temperatures and heat index values for Iowa locations and explains the effects of the decreased evaporation from high humidity on the body.
• ABC News: Getting Salty with Winter Road Maintenance: Describes the materials used to deice roads, including.