Precipitation of colloidal solutions

[Asmaa Mohammad]

Hello,
I read about the colloidal solutions in my chemistry book, and came across this sentence:

"Emulsoids (a type of colloidal solutions) are difficult to be precipitated, e.g. by concentrated solution of NaCl (removes H2O film by its osmotic power then it neutralize the charges)."

I don't understand the sentence and the book doesn't give a further explanation.

So I would appreciate if some one would explain it for me, and especially the "neutralize the charges" part.

Thanks in advance!

 

[Borek]

Colloidal molecules have slightly charged surface, and the electrostatic repulsion keeps them afloat (you can't precipitate them if they won't combine into larger aggregates). No idea why they call for osmotic pressure, but imagine adding small ions to the solution (like those from the NaCl dissociation). What will they do?

 

[Asmaa Mohammad]

but imagine adding small ions to the solution (like those from the NaCl dissociation). What will they do?

Hmm .. the small charged ions would be attracted to the colloidal molecules. And they will try to attach colloidal molecules to each other forming an aggregate, right?

No idea why they call for osmotic pressure

I have no idea too.

perhaps it is something related to the fact that water particles form a thin film surrounding the solute particles. But I can't go any further.

 

[Borek]

Hmm .. the small charged ions would be attracted to the colloidal molecules. And they will try to attach colloidal molecules to each other forming an aggregate, right?

Yes, once the repelling charges are neutralized aggregation becomes much easier.

 

[Asmaa Mohammad]

Yes, once the repelling charges are neutralized aggregation becomes much easier.

Then If I want to define "neutralization" in this case, How would it be?

 

[Borek]

Proton has a positive charge, electron has a negative charge, hydrogen atom is neutral.