[themonk]

I have a formula for a precipitant but don't follow what it exactly means.  

"Cooling the concentration solution to room temperature would cause precipitation of the double salt Na₇F(PO₄)₂*19H₂O."

What I do not understand is the "*19H2O". What exactly is the meaning of it? Where would all that water be located (evaporated, surrounding molecule)?

If this should be in Undergraduate Chemistry, please move it.

Cheers

Edit: I think I have also noticed when discussing crystallization.

[discodermolide]

I have a formula for a precipitant but don't follow what it exactly means.  

"Cooling the concentration solution to room temperature would cause precipitation of the double salt Na₇F(PO₄)₂*19H₂O."

What I do not understand is the "*19H2O". What exactly is the meaning of it? Where would all that water be located (evaporated, surrounding molecule)?

If this should be in Undergraduate Chemistry, please move it.

Cheers

Edit: I think I have also noticed when discussing crystallization.

The water is in the crystal lattice, water of crystallisation.

[Borek]

http://en.wikipedia.org/wiki/Water_of_crystallization

Edit: Disco beat me.

Note: it should be be not an asterisk, but a middot: NaF(PO₄)₂·19H₂O.