Please, will someone help me to understand this?

 

The literature describes removal of residual water from insoluble product by washing the product with concentrated salt water.

 

Can someone explain the chemical mechanism by which this works? Thanks!

 

imp

there are 2 main mechanisms to what`s sometimes called "Salting out", the Common Ion effect is one, another is simply solubility where the part that allows an ion to remain soluble is taken away by something else it prefers better.

the water is in your product, and you want it out.

 

If you bring your product into contact with salty water, the water in the product is attracted by the other water. Simply said: water molecules like other water molecules. The hydrogen of one molecule is attracted strongly by the oxygen of another molecule (this is called a H-bond). Making the water salty increases the polarity of the water phase. This attracts the water even more.

 

You're basically doing an extraction. You're extracting water from a product. But your solvent that you use for the extraction is water.

 

To find out which kinds of molecules like which kind of other molecules, I suggest you investigate the concept of "polarity".

 

The extraction of water doesn't work with every product. for example, if there's water in ethanol, washing with salty water will create a big ethanol-water-salt mix, and a very sad you.

water in Ethanol you would distill. but salt in water you can either add conc HCl(aq) and the salt will drop out OR you can just evaporate the water off. OR ethanol addition for an Ionic salt can also bring about a PPT reaction, but`s due to Hydrogen bonding.