1. Formula of a Hydrate

2. HYDRATE
An ionic compound that contains water molecules in its structure
The formula states how many mol of water molecules per one mol of ionic compound
Example: CuSo4  5 H20
Copper(II) sulfate pentahydrate
Na2CO310H2O
Na2SO410H2O
MgSO47H2O
ZnSO47H2O

3. CuSo4  5 H20

4. ANHYDRATE
The substance that remains after the water is removed from a hydrate
Example: CuSo4
Anhydrous Copper(II) sulfate

5. CuSo4

6. Prefixes 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9
nona 10
deca

7. Steps to find formula
Find the mass of anhydrate and water
Convert mass of both anhydrate and water to moles, respectively
Find the mole ratio of water to anhydrate
Write the formula and name

8. Example i
A calcium chloride hydrate has a mass of 4.72g. After heated for several minutes the mass of the anhydrate is found to be 3.56g. Determine the formula and name of the hydrate.
Calcium chloride: Ca2+ Cl−
CaCl2
Step 2: 4.72g hydrate
− 3.56g anhydrate
1.16g H2O
Step 3: 3.56g CaCl2 1mol CaCl2
110.98g CaCl2
1.16g H2O 1mol H2O
18.02g H2O
= molCaCl2
= mol H2O
SIG FIGS IN ANSWER MUST MATCH GIVEN!!

9. Step 4: Ratio mol H2O mol CaCl2 Step 5: CaCl2 2H2O Step 6: calcium chloride dihydrate ≈ 1

10. Example ii
A g sample of a hydrate of magnesium carbonate was heated, without decomposing the carbonate, to drive off the water. The mass of the anhydrate was found to be 7.58 g. What is the formula and name of the hydrate?

11. Example iii
What is the formula and name for a hydrate which consists of 76.9% CaSO3 and 23.1% H2O?