Every survivalist knows the importance of being able to remove the salt from saltwater. It’s a handy concept to understand, whether you’re stranded on a deserted island or just want to understand how evaporation works.
The second blog in our three-part series helps us understand how water is purified through evaporation.
Objective: understanding the multiple states of matter (solid, liquid gas) through water.
What you will need:
- Large pot
- Boil safe mug or container
- Aluminum foil
Step 1: Make salt water.
The first step to this experiment is actually making the salt water. You add salt to water, which will dissolve as you stir it. Warm water helps dissolve the salt faster, and you want to add enough salt to the water that it becomes overloaded and there is some left at the bottom that won’t mix.
Taste a little of the saltwater at this point to see how different it is compared to regular water.
Step 2: Pour the saltwater into a large pot on the stove. Place your boil safe mug into the pot, being careful not to get any of the saltwater into the mug. Cover the pot with aluminum foil, sealing the edges, leaving just enough slack to provide a slightly lower point in the middle. In this lower point place some ice cubes. Turn on the stove to bring the water to a boil.
Step 3: Watch carefully. Once the water starts to boil, set it on low-medium heat to maintain a simmer for about 10 minutes or until the ice cubes melt. Don’t let it boil dry!
Turn off the heat and let the whole thing cool without touching it for 20 to 30 minutes.
Step 4: Once cool, carefully remove the tinfoil. You may need to use some paper towel to soak up the melted ice cubes. You will notice there is now water in the mug, and a lot less water, that may be cloudy, in the pot.
One way to test the effects of the experiment is to repeat the taste test. Dip a finger in the mug of “evaporated water.” What do you notice? Now dip a finger in the remaining water in the pot.
The Science Behind Desalination and Saltwater
When you create the mixture at the beginning, the salt (NaCl) dissolves in water (H2O). There is no chemical reaction between the molecules. They retain their individual structures simply mixing together.
When you boil salt water it creates steam or water (H2O) in gaseous form. This gas rises during the boiling process, usually escaping into the air. When you cover the pot you capture that steam. The ice causes the steam to rapidly cool and being a lower point directs the cooled water to drip into the mug.
All the NaCl or salt is left in the original water, but becomes even more concentrated during the boiling process as molecules of H2O escape through evaporation.
Water Density Experiment
The next step will help us to test the density of water and show how the salt makes the water heavier. First add a bit of food coloring to each batch of water. Make sure you use different colors and keep track of what color corresponds to salt water and pure water. The idea is that you can visually see which water is which. Another way to test the difference between the water in the mug vs the water in the pot is to try layering the water to explore the density differences.
Water density is the ratio of weight to volume. A higher density means the same volume of saltwater weighs more than pure water.
Understanding Water Density
Now add a bit of saltwater to a test tube or small container, then carefully add some of the water from the mug to the test tube. Go slow, one drop at a time. For best results, use a pipette if you have access to one, or use a small spoon held against the wall of the test tube so the water gently flows down. You should notice that the freshwater layers on top of the saltwater.
On the left is the result when we put the fresh water in first, then saltwater, they will mix. But when we put the more dense saltwater in first, then the freshwater, the saltwater will layer with the freshwater.
Saltwater is heavier, or more dense, than freshwater. So when you carefully layer the two waters, they will remain separate with the freshwater floating on the more dense saltwater. But when you reverse the order, the waters mix because the more dense saltwater sinks immediately into the lighter freshwater.
Buoyancy is the ability for something to float in water. For example, a boat has a high buoyancy, or it would sink. Now, try testing the buoyancy and density properties of our waters another way. Try adding a potato to the waters and watch what happens.
The potato floats in the saltwater but sinks in the freshwater. Saltwater provides a higher buoyancy to the potato that the freshwater does not. This also means that the potato has a lower density than the saltwater.
In our potato experiment, the high density of the saltwater makes the potato float. This is also why it is easier for people to float in saltwater (like the ocean) compared to freshwater (at the pool).
CSWR uses a variety of methods to purify water from the contaminants that make their way in, whether minerals, chemicals or foreign objects. This process includes multi-step purification at our treatment plants and facilities.