Why can some ionic substances be "hydrated"????

[albertlee]

An ionic substance like CuSO4, if I pour some pure water on it, it turns blue,

 

my teacher explains this is that it is "hydrated", and what I am curious is

 

how do the water molecules bond to the ions of Copper Sulphate???

 

For sure, not all the ionic compounds can be "hydrated"...., like table salt, it will not be hydrated, but dissolved....

 

so, how come Copper Sulphate dont dissolve???

 

Any help??

 

Albert

[raivo]

I do not know answer to your question but it is rather common when two molecules connect to make hydrate or complex of some kind. Table salt CAN be hydrated but not at room temperature. Near the -20 in high humidity NaCl*2H2O may form. Water is not only solvent that may get bonded to salt molecules. Many organic solvents do the same in specific conditions .

[albertlee]

thx raivo by the way

 

Any body for more info???

 

thx in advance

[Guest Kshama Pai]

When an ionic compound dissolves, its ions become hydrated. That is, the water molecules are attracted to the ions. When it is allowed to crystallize, some of the water molecules become trapped in the crystal lattice structure of the ionic crystal. Because the ionic crystal lattice is uniform, the number of water molecules trapped becomes predictable for any given crystal. For Copper (II) sulphate, five water molecules become trapped for every copper ion and sulphate ion. We call that new crystal copper (II) sulphate pentahydrate.

 

By the solubility rule of ionic compounds, all sulphate salts dissolve except for a few exceptions. Copper sulphate will dissolve it will be represented as CuSO4 (aq) instead of CuSO4.5H2O.

[kingjewel1]

The hydrates of Cu compounds are due to water ligands. The water molecule makes a dative bond in the Cu's d orbital. Six of these H20 molecules can comfortably attack the Cu.

As mentioned above, H2O is the not the only ligand, EDTA being one of the strongest. Things like NH3- and CN- also are ligands.

[budullewraagh]

things with lone pairs on bent structures work well

[kingjewel1]

does anyone have a list of ligands from strongest to weakest or know where to get one¿