Why Can’t Salt Be Separated From Water by Filtration? 

Salt, also known as sodium chloride, is a mineral that is essential for human health. It is an important ingredient in many foods, including seasoning, as well as a preservative. It can be found in most countries around the world, from seawater to deep within the earth’s crust. 

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Its crystalline form is transparent and white, though it may be colored by traces of magnesium chloride or other impurities. It is non-volatile and odorless. It is a cation and an anion, and it can combine with other ions to form acids or bases. 

Why can’t salt be separated from water by filtration?

Since salt is a cation and water is a solvent, they are inseparable. However, they can be separated by evaporation or distillation. 

Distillation is the process of boiling salt water until the dissolved salt is left behind as a solid. The resulting liquid is called distilled water, which can be used for cooking or drinking. 

Another way to separate salt from water is by using reverse osmosis. This technique uses a semipermeable membrane to separate the water from the salt. While reverse osmosis can be more efficient than thermal distillation, it is not as environmentally friendly. 

Reverse osmosis is more expensive than thermal distillation, but it can produce more drinkable water in a shorter time and requires less energy to run. Unfortunately, it can also harm small ocean creatures and pump supersalty brine back into the water. 

Other ways to separate salt from water include evaporation and crystallization. In evaporation, the salt water is heated and evaporated off to leave behind sodium chloride crystals. In crystallization, the salt water is placed in a solution that is then heated until the salt crystallizes and can be removed from the solution. 

When you mix a solution of sodium chloride and rock salt, both the ions (sodium and chlorine) of the two salts recombine, leaving behind a new substance, called sodium chloride ion crystals. If the solution is then filtered, the crystallized sodium chloride will be removed and the remaining water will remain. 

You can use a straw to test this. Put a bit of the salt water into the straw and then take a sip. If you don’t taste any salt in the straw, the mixture is probably too diluted. 

If you do, try a different straw with the sand mixture and see if that changes the taste. You might find that it tastes a lot more like water than you did before. 


In a laboratory, a chemist might need to separate solutions. This might be done to separate the solute from the solvent after a chemical reaction has taken place or to remove some unwanted substances from a solution. 

The most common method of separating solutes from their solvent is by evaporation or distillation. Depending on the size of the separation and the desired results, these methods can be performed manually or by a machine. For a large-scale operation, reverse osmosis or multiple-stage evaporators can be used to ensure that all solutes are separated and the water is left clean.