Hydrated molecules?

Question

when something becomes hydrated. what happens to the molecules?

say u hydrated copper(II) sulfate
do the water molecules become part of the copper sulfate molecules? or what?

it says in a book that

"hydrated salts aren't really different from regular salts, since the water isn't actually a part of the core molecule. It's just a regular salt molecule with a water molecule "stuck" to it that just sort of tags along."

so whats the water molecule doing? and how is it "stuck" to the core molecule ?

Answer 1

The salt has a crystal structure that may look like a group of cubes put together.

The water molecules are trapped inside the empty space of the cubes, held in place by electrostatic charges. There is no real chemical bond. A little bit of heat and the water molecules escape. If you have some moisture in the air, the water will eventually go back inside the cubes.

Answer 2

Cu2SO4 * 5H2O

Well, the 5 water molecules loosely bond to the SO4 by sharing electrons. This bond is extremely weak, however, and can be broken up by simply heating the compount to the boiling point of water (212 F).

The water molecules really do 'tag along'. Simple photons from sunlight can cause water molecules to bond to the Cu2SO4, or leave it.

And the word is 'hydroscopic' - water attractor.

Silica is the prime example of this.

Each Silica molecule can attract something like 20 water molecules. In the industry I work in, we use Silica as a 'dessicant' or dehydrator. It will actually attract so much water on a trans-oceanic voyage that a 4 ounce bag of it will turn into a gel, and weight over one pound.

Answer 3

Many ionic compounds have loosely bonded water that crystallizes with the compound
It can be driven off by heating and but the metal and nonmetal ions stay together.

eg: MgSO4 .7H20 is a hydrate which upon heating gives the anhydrous salt MgSO4 + 7 H20

The water is part of the crystal structure and when you heat the compound the crystal structure changes. Sometimes the color of the crystal will change as well.