Evaporating Seawater

Dissolve table salt in warm water to make a saturated solution, then leave the solution in a shallow container for days. As water evaporates, the remaining liquid becomes supersaturated and salt recrystallizes on the dish and along the waterline.

1. Set a shallow, clear bowl on a stable surface. Pour in warm water (not boiling).
2. Stir in table salt a spoonful at a time until some grains no longer dissolve (a sign of saturation). Let undissolved grains settle.
3. (Optional) Pour the clear solution into a clean dish, leaving any grit behind.
4. Use a dry-erase marker to draw a waterline on the outside of the dish.
5. Place the dish somewhere warm and undisturbed with good airflow (away from pets and small children). Do not cover it.
6. Observe daily: record the water level by adding a new mark and note any salt deposits forming on the sides and bottom.
7. After about a week (or when most water has evaporated), examine the salt crystals that have formed. Gently scrape a few onto dark paper to observe shapes.

To Separate a Saltwater Mixture by Evaporation - Simple Science and Maths:

Science experiment: Separating mixture by EVAPORATION - argenicz:

📄 A Super Simple Salt Water Evaporation Experiment - Homeschool by Joanna: https://joannacinnamon.com/a-super-simple-salt-water-evaporation-experiment/

• Run two dishes: one uncovered at room temperature and one loosely covered, and compare evaporation rate and crystal size.
• Compare shallow wide dishes vs deeper narrow cups to test how surface area affects evaporation time.
• Start one dish with a few grains of dry salt (“seeds”) and another with none to see how seeding changes where crystals form first.
• Try different salts (table, kosher, sea salt) and note differences in crystal clarity and shape.
• Add a simple measurement: weigh the empty dry dish, then the dish plus dry crystals at the end to estimate salt recovered; graph waterline height vs day.
• Evaporate water in a cooking pot on the stove.

• Adult supervision required when using warm water and glass/ceramic dishes.
• Do not taste the solutions or crystals prepared for the experiment; label the dish “Do Not Eat.”
• Keep setup out of reach of young children and pets; clean spills promptly—saltwater can damage some surfaces.
• If you heat water on a stove, use oven mitts and place hot containers on heat-safe surfaces.

• Why doesn’t the salt evaporate with the water? (sodium chloride is nonvolatile at room temperature; only the water molecules evaporate.)
• Why do crystals form along the rim as the waterline drops? (evaporation at the contact line leaves salt behind; capillary action draws solution up the sides.)
• How do temperature, airflow, and surface area change the evaporation rate? (warmer air, more airflow, and larger surface area speed evaporation.)
• What evidence shows the solution became supersaturated before crystals formed? (clear solution at first, then sudden appearance/growth of solid as water volume decreased.)
• If you wanted to recover fresh water from salt water, what extra step would you need? (collect and condense the water vapor—distillation—rather than just evaporating it.)