Chem161, unit4, Hydrated Ionic Compounds

What is a hydrate?

An ionic compound that contains water molecules within its crystal structure.

What happens when a hydrate is heated?

The water is released, forming an anhydrous (without water) compound.

What does the prefix "mono-" mean in hydrates?

1 water molecule (e.g., CuSO₄·H₂O → copper(II) sulfate monohydrate).

What does the prefix "di-" mean in hydrates?

2 water molecules (e.g., CaCl₂·2H₂O → calcium chloride dihydrate).

What does the prefix "tri-" mean in hydrates?

3 water molecules (e.g., AlCl₃·3H₂O → aluminum chloride trihydrate).

What does the prefix "tetra-" mean in hydrates?

4 water molecules (e.g., MgSO₄·4H₂O → magnesium sulfate tetrahydrate).

What does the prefix "penta-" mean in hydrates?

5 water molecules (e.g., CuSO₄·5H₂O → copper(II) sulfate pentahydrate).

What does the prefix "hexa-" mean in hydrates?

6 water molecules (e.g., CoCl₂·6H₂O → cobalt(II) chloride hexahydrate).

What does the prefix "hepta-" mean in hydrates?

7 water molecules (e.g., NiSO₄·7H₂O → nickel(II) sulfate heptahydrate).

What does the prefix "octa-" mean in hydrates?

8 water molecules (e.g., BaCl₂·8H₂O → barium chloride octahydrate).

What does the prefix "nona-" mean in hydrates?

9 water molecules.

What does the prefix "deca-" mean in hydrates?

10 water molecules (e.g., Na₂CO₃·10H₂O → sodium carbonate decahydrate).

How do you name hydrates?

Name the ionic compound first, then add a prefix for the number of water molecules followed by "hydrate."

Example — Na₂CO₃·10H₂O

Sodium carbonate decahydrate.

Example — CoCl₂·6H₂O

Cobalt(II) chloride hexahydrate.

Example — CuSO₄·5H₂O

Copper(II) sulfate pentahydrate.

Example — BaCl₂·2H₂O

Barium chloride dihydrate.

What is an anhydrous compound?

The compound remaining after all water has been removed from a hydrate.

How do you write the formula for a hydrate?

Use a dot between the salt and water molecule count (e.g., Na₂SO₄·10H₂O).

What is the difference between a hydrate and an anhydrous salt?

A hydrate contains water molecules; an anhydrous salt does not.

Where do we put the "water part" in the name of a hydrate?

After the name of the ionic compound — add the correct prefix + “hydrate.”
(Example: CuSO₄·5H₂O → copper(II) sulfate pentahydrate)

Fr

is there a dot when doing notation for a water hydrated compound?

yes..

• Example

• MgSO₄·4H₂O