hydrates lecture

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HydratesLeah Abittan MSc

lbensimo@nova.edu

Hydrate definition

A hydrate is a compound that has a specific number of water molecules bound to its atoms

Opals

Naming Hydrates

• Write the compound and the hydrate connected by a dot

Sodium carbonate decahydrate

Naming Hydrates

Analyzing a Hydrate

• The hydrate can be removed from the compound through heat

• Cobalt (II) Chloride is a pink solid that turns deep blue when heated and water is removed (anhydrous form)

Formula for a Hydrate

• 1. Determine the number of moles of water associated with one mole of hydrate– 5 g sample of Barium Chloride Hydrate (BaCl2•xH20)

– After heating, the weight of the anhydrous sample is 4.26 g

– 5 g – 4.26 g = 0.74 g H20

– Determine moles of H20 and BaCl2 ratio

Hydrate Example

• A mass of 2.50 g of blue, hydrated copper sulfate (CuS04•xH20) is placed in a crucible and heated. After heating, 1.59 g white anhydrous copper sulfate remains. What is the formula for the hydrate? Name the hydrate.

Hydrate Example Cont’d• 1. Hydrous copper sulfate is 2.50 g

• 2. Anhydrous copper sulfate is 1.59 g

• 3. 2.5 g – 1.59 g = 0.91 g of hydrate

• 4. 0.91 g water lost, 1.59 g copper sulfate

Hydrate Example Cont’d

• 5. Calculate the moles of Copper sulfate and the moles of water lost

• 6. Determine the molar ratio

• 7. Setup the formula and name it

Practice Problems-Appendix D

• A hydrate is found to have the following percent composition

– 48.18% MgS04 and 51.2% H20

– What is the formula and name for this hydrate?

MgS04•7H20 Magnesium Sulfate heptahydrate

Practice Problems-Appendix D

• If 11.75 g of the common hydrate cobalt (II) chloride is heated, 9.25 g of anhydrous cobalt chloride remains. What is the formula and name for this hydrate?

CoCl2•2H20 Cobalt (II) Chloride dihydrate

Uses of Hydrates

• Drying agents due to hygroscopic nature (absorb water from environment)

• Solar energy (Na2S04•10H20)

Questions

Thank You!

References

• http://geology.com/gemstones/opal/#precious

• Chemistry textbook

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