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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.
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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 .