[according_chef]

How can I make 500ml of 0,25 M Nickel (II) chloride solution from NiCl2 ∙ 6 H2O salt. I have no idea if and how I should include the water of crystallization into my calculations.

[sjb]

How would you make a 1 litre of a 1M solution of NaCl, for instance?

[according_chef]

Yes I do know how to use molar mass etc., but my question was if the water already present in the salt crystals should be taken into concideration.

[Babcock_Hall]

Ordinarily the molecular weight includes the waters of crystallization, but you can check the math easily enough.

[DrCMS]

Yes I do know how to use molar mass etc., but my question was if the water already present in the salt crystals should be taken into concideration.

If you have anhydrous NiCl and NiCl.6H₂O and you take the same weight of each and make that up to 1L with water do you think you will  have the same number of moles of NiCl in each solution?

[Enthalpy]

The water of crystallization
1) Increases the amount of water in the solution
2) Increases the mass of the crystal at identical number of moles.

[Babcock_Hall]

Molarity is moles per liter of solution.  If one uses a hydrated salt, one will add slightly less water than if one uses a hydrated salt, but the final volume will be the same.