1. The Formula for a Hydrate
Chapter 11 Notes Part 3
The Formula for a Hydrate

2. What is a Hydrate?
A Hydrate is compound that has a specific number of water molecules bound to its atoms.

3. Formula for a Hydrate
The number of water molecules associated with each formula unit of the compound is written following a dot:
Na2CO3•10H2O= Sodium Carbonate decahydrate
FePO4•4H2O= Iron(III) phosphate tetrahydrate

4. Prefixes for hydrates are listed on p 338
Prefix of H2O
Mono Di
Tri
Tetra
Penta
Hexa
Hepta
Octa
Nona
Deca

5. Analyzing a Hydrate
To analyze a hydrate, you must drive off the water of hydration
Anhydrous = without water (the H2O has been driven off by heating)
Mass of hydrate cmpd – mass of anhydrous cmpd = mass of H2O

6. Determining formula of a hydrate
Mass of anhydrous cmpd = mole of cmpd
Molecular weight of cmpd
Mass of H2O = mole of H2O
MW of H2O

7. Example
A hydrate is found to have the following composition: 48.8% MgSO4 and 51.2% H2O What is the formula and name of this hydrate?

8. Uses for Hydrates
Packaging materials with desiccants that absorb water from the air and prevent moisture accumulation
A Desiccant is a substance that promotes drying
Desicants are the anhydrous form of the hydrate- used to absorb water into its crystal structure