How is salt separated from water? For centuries this question has puzzled sailors stranded at sea and science fair students alike. The answer is simple: through evaporation. When you evaporate salt water (either with natural or artificial heat), only the water forms water vapor, but the salt remains. With this in mind, it's pretty easy to separate salt from water with the kinds of common materials you can have around the house.
Method 1 of 3: Doing a Basic Evaporation Experiment
Step 1. Heat water and add salt to make salt water
It's easy to see the principles of evaporation in action by performing this simple experiment. To get started, you will need some table salt, tap water, a pot, a piece of black construction paper, and a stove. Pour a couple of cups of water into the pot and put it on a hot burner. Wait for the water to heat up; it doesn't need to boil, but the hotter it is, the faster the salt will dissolve.
The reason hot water is great for dissolving salt (and other chemicals) has to do with the movement of the molecules that make up water. When water is heated, these molecules move faster, collide with more salt molecules and separate the salt crystals
Step 2. Add salt until it no longer dissolves
Continue adding tablespoons of salt and stir to dissolve it. Eventually, you will reach a point where the salt will no longer dissolve, no matter how hot the water is. This is called the "saturation" point of the water. Turn off the stove and let the water cool down a bit.
When the water reaches its saturation point, it will no longer be able to dissolve the salt on a molecular level: so much salt has dissolved that there is no longer any chemical potential for the water to split the new salt crystals
Step 3. Using a spoon, scoop the water onto a dark card
Using a spoon or ladle, scoop some salt water onto a dark card stock. Place this paper on a plate to prevent the table or surface it is on from getting wet. Now you just have to wait for the water to evaporate. This process will be a little faster if you leave the cardboard somewhere where the sun's rays can reach.
Don't waste your leftover salt water. There are many things you can use it for, for example, you can use it to cook an egg, boil potatoes, preserve spinach and even so that you can peel the nuts better
Step 4. Wait for the salt to form
As the water evaporates, miniature salt crystals should form. You will see them small, shiny and with light or white scales on the surface of the cardboard. Congratulations! You just separated the salt from the water.
You have all the freedom to scrape some salt off your cardboard to salt the food. It's okay if you eat it, but make sure there are no cardboard shavings in your food
Method 2 of 3: Making a Distiller
Step 1. Start by boiling a pot of salty water
The simple experiment we saw earlier showed how to get the salt out of the water, but what if you want to also keep the water without salt? Distillation is the answer. Distillation is the process of heating a liquid to separate it from the chemicals that are dissolved in it, then collecting the condensation, which must be relatively "pure." In this case, we will start by making a couple of cups of salt water (check the instructions mentioned above), heat it and bring it to a boil.
Step 2. Cover the pot
Next, find a lid for your pot (it doesn't have to fit perfectly). Balance the lid on the pot so that that part hangs over the rim. Try to position the lid so that the part hanging from the edge is the lowest point on the lid. Notice how condensation forms on the bottom of the lid and begins to drip.
As the salty water boils, the (unsalted) water will turn to steam and flow out of the pot. When it reaches the lid, it will slowly cool and form liquid condensation (water) on the bottom of the lid. This water does not contain salt, so you only have to gather it to have water without salt
Step 3. Collect the water in a container
As the water goes down, the condensation at the bottom of the lid will obviously collect at the lowest point of the lid. Once enough condensation has accumulated, droplets will begin to form and fall. Put a container under this place so that the drops of distilled water fall there.
If you want, you can also put a long, thin metal or glass object (like a stick or thermometer) from the container to the bottom of the lid. The water will travel through this object until it reaches the container
Step 4. If necessary, repeat the process
As the salty water boils in the pot, the more distilled water will be in your container. Much of this water will be salt free. However, in some situations, a small amount of salt may remain. In this case, you can do a double distillation: boiling the distilled water that you collected in the same way that you boiled the salty water to separate the salt.
Technically, this water is safe to drink. However, unless you are sure that the lid of the pot and the container in which you collected the water (the thin metal or the glass rod, if you used them) are clean, you may not want to drink the water
Method 3 of 3: Using Uncommon Methods
Step 1. Use reverse osmosis
The above methods are not the only ways to separate salt from water, they are just the most convenient for most people to do at home. It is also possible to separate the salt from the water with other methods that require specialized materials. For example, a technique called "reverse osmosis" can extract salt from salt water by pushing the water through a permeable membrane. This membrane acts as a filter and only allows water molecules to pass through and excludes contaminants (such as salt).
Sometimes reverse osmosis pumps are sold for residential use, but they are usually used for recreational purposes like camping as well. Pumps can be a bit pricey. They usually cost several hundred US dollars
Step 2. Add decanoic acid
Another way to separate salt from water is through a chemical reaction. For example, research has shown that treating salt water with a chemical called “decanoic acid” is a reliable way to extract the salt. After adding the acid, heating slightly, and allowing to cool, the salt and other impurities will “fall” out of solution (ie, they will solidify and sink to the bottom). When the reaction is complete, the water and the salt will be in two different layers, making it easy to extract the water.
You can buy decanoic acid in chemical stores, and a bottle costs around $ 30-40
Step 3. Use electrodialysis
Using the power of electricity, it is possible to extract particles (such as salt) from the water. This is done by immersing a negatively charged anode and a positively charged cathode in the water and separating them with a porous membrane. The electrical charge of the anode and cathode “attracts” the dissolved ions (such as those that make up salt) as if they were magnets, leaving the water relatively pure.
Keep in mind that this process does not necessarily remove bacteria or other contaminants from the water, so another treatment may be needed to obtain potable water from this method. However, recent research has been promising and suggests techniques that do kill bacteria as part of the process
Do not use seawater unless it is a necessity. In addition to salt, it can also contain minerals, organic material, and other contaminants that will make complete purification difficult
- Be careful every time you boil the water in the kitchen. If you have to touch the hot pot or saucepan, be sure to use oven mitts or a towel to protect yourself.
- Don't drink salt water if you are lost in nature. The human body needs more water to get rid of salt than it actually supplies, so salt water can make someone much more dehydrated.