1. Hydrates Water molecules can adhere to ions as the solid forms The water becomes trapped and is part of the crystal Opals and other gems are common hydrates & get their color from the water. Hydrates have a specific amount of water associated with each formula unit

2. Hydrates The amount of water is indicated in the formula: Na 2 CO 3. 10H 2 O This means there are 10 moles of water for every mole of the ionic compound or 10 molecules of water for each formula unit The water must be calculated into the molar mass of the substance The name is sodium carbonate decahydrate

3. Formula for a Hydrate Need to determine the number of moles of water associated with one mole of the hydrate Heat the hydrate to drive off all water and form the anhydrous compound Use the difference in mass between the hydrate and anhydrous compounds to determine the mass of water & the cpd Use these masses to calculate the moles of each then find the ratio between them

4. Example You have a 5.00 g sample of a hydrate of barium chloride. After heating, the dried barium chloride has a mass of 4.26 g. What is the formula and name for this hydrate?

5. Try It 1.A mass of 2.50 g of blue, hydrated copper (II) sulfate is placed in a crucible and heated. After heating, 1.59 g white anhydrous copper (II) sulfate remains. What is the formula and name for the hydrate? 2.Gypsum is hydrated calcium sulfate. A 4.89 g sample of this hydrate was heated, and after the water was driven off, 3.87 g anhydrous calcium sulfate remained. Determine the formula and name the compound.