1. Water of crystallisation
L.O.:
Explain the terms anhydrous, hydrated and water of crystallisation.
Calculate the formula of a hydrated salt.

2. Workshop today at 1:45pm: Winifred Henry Anna Keverne Esther Adeduntan

3. Copper sulfate
Copper sulfate comes in a hydrated form (copper sulfate pentahydrate) and a anhydrous form

4. Anhydrous substances
Many substances will absorb water from the atmosphere, like NaCl, these are called hygroscopic substances
An anhydrous compound is one which has no water molecules inside of it
To make an anhydrous substance you can either heat it to evaporate off the water, or you can dry it in a drying cabinet

5. Writing out the formula for hydrated compounds
There are two ways in which a formula can be written if it is a hydrated compound:
Empirical formula, Which you know and love OR
Dot formula, So copper sulfate pentahydrate becomes Cu SO3 • 5H2O
NOTE: This dot is very important!!!!!

6. Hydrated substances and water of crystallisation
Some substances can trap water molecules inside of them.
The water contained is called the water of crystallisation

7. Finding the formula of hydrated copper(II) sulfate
Note: see worked example in page 27

8. FeSO4·xH2O Exp 1 Exp 2 Mass of crucible
Mass of crucible + hydrated salt
Mass of hydrated salt
Mass of anhydrous salt
Mass of water lost

9. FeSO4·xH2O Exp 1 Exp 2 Mean mass Mass of anhydrous salt
Mass of water lost

10. FeSO4·xH2O Mean mass Mass of anhydrous salt 1.51 g Mass of water lost
Calculate amount in moles of anhydrous salt
n (FeSO4) = 1.51/ = 0.01
2) Calculate the amount in moles of water.
n (H2O) = 0.54/18 = 0.03
3) Calculate molar ratio
FeSO4 : H2O = 0.01: 0.03
4) Divide be the smallest number 0.01: 0.03 = 1:3

11. Salt
Ions present
CaCl2•2H2O
ZnCl2•6H20
Ba(OH)2•8H2O
Cu SO3 • 5H2O
YSO3•6H20
Na Z
XSO4

12. Hydrated salt Mass of anhydrous salt Water lost Identity of salt
XCl•2H2O
5.86 g
9 g
XSO4•3H20
40.53 g
16.2
X NaCl
k SO4

13. Other examples of hydrated compounds:
Cobalt chloride hexahydrate
Sodium sulfate decahydrate
Write out the formula for these compounds using the “dot formula” notation

14. Convert these into the Dot Formula
Calcium chloride dihydrate
Calcium chloride hexahydrate
Zinc chloride hexahydrate
Barium hydroxide octahydrate

15. Answers Calcium chloride dihydrate = CaCl2•2H2O
Calcium chloride hexahydrate = CaCl2•6H2O
Zinc chloride hexahydrate = ZnCl2•6H20
Barium hydroxide octahydrate = Ba(OH)2•8H2O

16. Write these out in Dot formula
Hydrated Cobalt chloride CoCl2H12O6
Hydrated Calcium carbonate CaCH6O6
Hydrated Magnesium sulphate MgSH12O10