[RGraham9]

Hi , I have a few questions regarding Crystallisation are :
1. What are the differences between Crystallisation and Recrystallisation ? Is Crystallisation basically the process of separating a pure solid from a solution that it is dissolved in while Recrystallisation is the process of purifying an impure solid by dissolving it in a suitable solvent and then carrying out Crystallisation to obtain a pure version of the solid ?
2. What is the relation between water of Crystallisation and Crystallisation ? Do crystals formed by Crystallisation have water of Crystallisation in them ? What happens if I decide to heat the crystal (if it has water of Crystallisation in them) ?

Thank you ! Appreciate the help guys !

[AWK]

http://www.wikiwand.com/en/Crystallization
https://www.wikiwand.com/en/Recrystallization_(chemistry)

[aga]

There is no difference, apart from Re-crystallisation being the crystallisation of crystals you made earlier, solvated again, then crystallised again.

The reason people do this is to get the crystals as Pure as possible by this process.

What happens, if done correctly (see the links in the post above for details) is that the major solvated substance slowly crystallises, leaving all the crap (dunno the IUPAC name for that) in solution, which you simply pour off.

Take those crystals you just made, dissolve them in a minmum of hot solvent, maybe filter if it's got big bits in it, and allow to crystallise again, and you've done a 'recrystallisation', purifying your substance quite a lot in the process, although a lot of the substance is also lost in the supernantant liquid that got poured off.

How many times this is done is a balance between Quantity and Quality.

More recrystallisations = higer purity = less grammes, and vice versa.

Edit:

Water of Crystallisation is the water that the substance grabs in order to form it's preferred crystal matrix.

For example, Aluminium Sulphate is quite 'promiscuious' in it's choice of exactly how many water molecules it will take into it's crystal matrix : it will happily take 2 water molecules, however 14.3 is quite common.

Copper sulphate is generally found in the .5H₂O blue crystal form