1. HYDRATES
Unit 7 Lesson 3

2. HYDRATES
Ionic compound that has water incorporated into its crystal structure

3. HYDRATES Written as MgSO4●7H2O
Read as “Magnesium Sulfate Heptahydrate”
Means for every one MgSO4 you have 7 water molecules.
Notice the prefixes we learned for naming covalent compounds are used to tell how many H2O molecules you have
If finding the molar mass, include the water!

4. HYDRATE PRACTICE Magnesium nitrate Tetrahydrate
Name the following Hydrates and find their molar masses
CuSO4 • 5H2O
(16) + 5(18.016) = g/mol
ZnCl2 • 3H2O
(35.45) + 3(18.016) = g/mol
Mg(NO3)2•4H2O
(14.01) + 6(16) + 4(18.016) = g/mol
Copper(II)sulfate Pentahydrate
Zinc chloride Trihydrate
Magnesium nitrate Tetrahydrate

5. DETERMINING THE FORMULA OF A HYDRATE
Example: Find the formula of a hydrate that is 48.8% MgSO4 and 51.2% H2O
Step 1 – assume exactly 100 grams
48.8 g MgSO4 and 51.2 g H2O
Step 2 – calculate moles
48.8 g MgSO4 (1 mol/120.38g) = .405 moles MgSO4
51.2 g H2O (1mol/18.02g) = 2.84 moles H2O
Step 3 – calculate mole ratio by dividing by smallest number of moles
.405/.405 = 1 mole MgSO4
2.84/.405 = 7.01 moles H2O
So there are 7 moles of water per 1 mole of MgSO4
MgSO4●7H2O

6. EXAMPLE
A hydrated Cobalt (II) Chloride sample has a mass of 11.75g. After being heated (to remove all water and become anhydrous) the mass is 9.25 g. What is the formula for the hydrate?
9.25 g CoCl2 and ( ) = 2.50 g H2O
CoCl2 = (35.45) = g/mol
H2O = 2(1.008) + 16 = g/mol
9.25 g CoCl2 x 1mol/ g = mol CoCl2
2.50 g H2O x 1mol/ g = mol H2O
0.0712/ = 1 mole CoCl2
0.139/ = 1.95 moles H2O
CoCl2 •2H2O

7. EXAMPLE: FINDING MASS PERCENT FROM A HYDRATE FORMULA
Determine the mass percent of the anhydrous portion and the water in the hydrate:
Na3PO4 •10H2O
Find the mass of the anhydrous Na3PO4 portion: (22.99) (16) = g/mol
Find the mass of the ten attached waters: (18.016) = g/mol
Find the mass of the entire hydrate Na3PO4•10H2O: g/mol g/mol = g/mol
Mass percent of the anhydrous: (163.94g/mol/344.10g/mol)100 = 47.6% anhydrous Na3PO4
Mass percent of the water:
(180.16g/mol/344.10g/mol)100 = 52.4% water