Hydrates (11.5)

• Hydrate- compound with a specific amount of water molecules bound to it

• Hydrates are often used as drying agents or desiccators because they can absorb moisture

• Silica gel- used in electronic equipment packaging, cat litter

• Chemicals that do not contain water in their structures are called anhydrous (without water)

• Hydrates are easy to spot because their formulas show the water molecules

Anhydrous cobalt (ii) chloride Cobalt (II) chloride hexahydrate

CoCl2 CoCl2 x 6H2O

To determine hydrate formula

1. Determine moles of water and of anhydrous compound

2. Find x = moles of water

moles of anhydrous compound

3. Plug in x

Formula for compound X H2O

• A mass of 2.50 g blue hydrated copper sulfate (CuSO4 x XH2O) is place in a crucible and heated. After heating, 1.59 g of copper sulfate remains. What is the formula for the hydrate?

2.50 = CuSO4 + H2O CuSO4= 1.59 g

2.50 = 1.59 + H2O H2O = 0.91 g

• CuSO4 = 63.5 + 32.1 + 4 x 16 = 159.6 g/mol

• CuSO4 = 1.59 / 159.6 = 0.010 mol

• H2O = 2 x 1 + 16 = 18 g/mol

• H2O = 0.91 / 18 = 0.050 mol

• X = 0.050 / 0.010 = 5

CuSO4 x 5H2O

What is the mole ratio of the hydrate CuSO4 x ___H2O, if the anhydrous mass of

CuSO4 is 25.42g and mass of water is 14.3 g?

• CuSO4 = 63.5 + 32.1 + 4 x 16 = 159.6 g/mol

• CuSO4 = 25.42 / 159.6 = 0.159 mol

• H2O = 2 x 1 + 16 = 18 g/mol

• H2O = 14.3 / 18 = 0.79 mol

• X = 0.79 / 0.159 = 4.96 ~ 5

CuSO4 x 5H2O

1:5

What is the mole ratio of hydrate Na2CO3 x ____ H2O, if the original mass of the hydrated Na2CO3 was 43.69 g and the mass of the anhydrous Na2CO3 is

16.19g?

• Hydrate = anhydrous + H2O

• 43.69 = 16.19 + H2O

• H2O = 27.50 g Na2CO3 = 16.19 g

• Na2CO3 = 2 x 24.3 + 12 + 3 x 16 = 108.6 g/mol

• Na2CO3 = 16.19 / 108.6 = 0.15 mol

• H2O = 2 x 1 + 16 = 18 g/mol

• H2O = 27.50 / 18 = 1.5 mol

• X = 1.5 / 0.15 = 10

Na2CO3 x 10 H2O