1. Ch. 10 – The Mole
Hydrates

2. A. Hydrate Definition
A compound that has water molecules attached to it
“Hydrate” means with water
Anhydride is the substance with the water removed

3. B. Hydrate Examples Magnesium sulfate heptahydrate MgSO4 • 7H2O
Barium chloride trihydrate
MgSO4 • 7H2O
(16.00) + 7(18.02)
BaCl2 • 3H2O
(35.45) + 3(18.02)
= g/mol
= g/mol

4. B. Hydrate Examples sodium carbonate decahydrate Na2CO3 • 10H2O
sodium carbonate monohydrate
Na2CO3 • 10H2O
2(22.99) (16.00) + 10(18.02)
Na2CO3 • H2O
2(22.99) (16.00)
= g/mol
= g/mol

5. C. Percent Composition of a Hydrate%
Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O.
Known:
Mass of H2O in 1 mol compound = 2[2(1.01g) g] = g H2O
Molar Mass = g + 2(35.45 g) g = g
Unknown:
% H2O = ?
36.04 g/mol
g/mol
%H2O =
 100 =
24.51%
H2O

6. D. Finding Hydrate Formulas in Lab
To determine the formula of a hydrate experimentally, we must calculate the mole: mole ratio of the water portion compared to the anhydride portion
An anhydride is the substance that remains after the water is removed from a hydrate.
When a hydrate is heated the water molecules are driven off as steam, leaving behind the water-free anhydride

7. D. Finding Hydrate Formulas in Lab
Record the mass of the hydrate.
Heat the hydrate and record the mass of the anhydride .
Calculate the mass of the water that was present:
mass of H2O = mass of hydrate – mass of anhydride
Convert mass of anhydride and mass of water to moles
Divide moles of water by moles of anhydride for value of x
anhydride formula  x H2O

8. E. Hydrate Lab Calculation
A calcium chloride hydrate has a mass of 4.72 g. After heating for several minutes the mass of the anhydride is found to be 3.56 g. Determine the formula for the hydrate.
GIVEN:
hydrate =
4.72 g
Anhydride =
3.56 g
Formula = ?
WORK:
H2O = 4.72 – 3.56 = 1.18 g
3.56 g CaCl2
1 mol CaCl2
g CaCl2
= mol CaCl2
mol
= 1
1.18 g H2O
1 mol H2O
18.02 g H2O
= mol H2O
= 2
CaCl2  2H2O