[Donaldson Tan]

Acetone((CH3)2CO)& H2O are completely miscible liquids.Addition of NaCl to acetone/H2O mixture cause the separation of two liquid phases.Rationalise this fact.

[gregpawin]

You got me man.  In fact I thought solubility with liquids was straightforward.  I thought there's the polar solvents and the non-polar solvents.... they don't mix.  Now I just learned that acetone mixes with everything pretty well and diethyl ether mixes with hexane.  What about ether and alcohols? and with water?  Will someone give me a chart or something that tells me what solvents mix with what!

[jdurg]

My only guess would be that the addition of the sodium chloride, thus making a highly ionic solution, would cause the water molecules which could normally solvate the acetone molecules to instead solvate the chlorine and sodium ions.  This makes it difficult for the acetone to remain in solution with the water, thus causing the separation.

[Mitch]

I'm going with Jdurg on this one.

[AWK]

The salting out process is used for reducing the mutual partial miscibility of two liquids but sometimes also work with solution of miscible liquids.
See: http://chemeducator.org/bibs/0001001/00010009.htm

[GCT]

Acetone((CH3)2CO)& H2O are completely miscible liquids.Addition of NaCl to acetone/H2O mixture cause the separation of two liquid phases.Rationalise this fact.

I suppose through the break up of the hydrogen bonds btw acetone and water.  Water, I believe, forms a octahedral complex with six chlorine anion, which would add significant favorability and probably proceeds over the hydrogen bond formation, water and acetone, (which is somewhat disorganized and non-reciprocal, notice how water by itself dissolves chlorine anions despite attractions to other water molecules) due to entropical reasons.