Hydrates

• Some substances, which we haven’t yet seen, are hydrates.– This means that they contain water

within their chemical bonds.• Because of this, their chemical formulas

must reflect the additional water.• To include “waters of hydration” in a

chemical formula, simply add a dot (•) and put the number of water molecules after it.

• Example next slide…

Hydrates

• Example: CoCl2 is cobalt (II) chloride. However, there are many times when this compound gains six water molecules.

• Therefore, we write the compound as CoCl2•6H2O• Its name is cobalt (II) chloride hexahydrate.

– If it had five water molecules, it would be cobalt (II) chloride pentahydrate. You get the idea.

• When describing a compound that is not hydrated, sometimes the term anhydrous is used.

• Example: CoCl2 on its own is anhydrous cobalt (II) chloride.

Hydrates

http://en.wikipedia.org/wiki/Hydrate

Hydrates: One Last Thing

• When calculating molar mass (or formula mass) of a hydrate, add the mass of water to the rest of the formula’s mass.– I know it looks like a multiplication

symbol, but don’t do that. That’d be bad .