Are you looking for a good science project that is both fun and easy? We won third place with this interesting science experiment. In this project, you turn salt water in to fresh water within a day, teaching vaporization, evaporation and condensation. The accompanying poster can depict shipwrecked sailors in need of fresh water, making the project both educational and entertaining as well.
Pour two cups of water in to a large bowl. Add three teaspoons of table salt to the water and stir. Now, place a tea cup in the middle of the bowl of water. Make sure the water level in the bowl is below the top of the tea cup. Place plastic wrap over the bowl and secure it with a large rubber band for a nice tight seal. Place a rock or similar weight on top of the plastic, directly over the tea cup. The will enable the condensation to drip down in to the tea cup. Take a picture of your experiment before the condensation begins!
Now, carefully place your bowl in direct sunlight. Do not let the salt water to spill in to the tea cup! If it is too cold outside for evaporation to occur, bring your bowl in and place it on a heater, clothes dryer or other warm and safe source. Check your bowl the next day and take a picture of it for your presentation. If there is a lot of condensation on the plastic, gently tap the weight on top of the plastic, causing the condensation to flow downwards and in to the tea cup.
Carefully remove the plastic wrap and get ready for the taste test! First, taste the water in the large bowl. Salty! With a different spoon, taste the water in the tea cup. Amazingly, the water is fresh – not a single trace of salt!
This experiement demonstrates a few things. When you add salt (solute) to water (solvent) they become a solution. The solar (or other) heat causes the water to evaporate in to a gas. Since the salt is heavier than the water, the salt remains in the bottom of the bowl. The evaporated water then cools, turning back into its original form, resulting in condensation on top of the plastic. This fresh water then runs down the plastic and drips in to the tea cup.