Honors Chemistry Lab
Name:
Date:
Water of Hydration
Objective: To study the properties of hydrates and determine the amount of water in a
hydrated compound.
Apparatus
Balance, Bunsen burner, crucible and cover, evaporating dish, clay triangle, tongs,
goggles.
Chemicals
Hydrated copper(II) sulfate compound.
Introduction
Most solid chemical compounds will contain some water if they are exposed to
the atmosphere. Some compounds contain larger amounts of water that is chemically
bound to the crystal. This water is called water of hydration and is usually bound to the
cations in the salt. The water molecules in a hydrate are removed easily by heating to a
temperature above the boiling point of water. This often results in a color change for
some compounds. Some hydrates, such as CoCl2, lose water to the air in a process called
efflorescence. Other hydrates can absorb water from the air or other sources so strongly
that they can be used to dry liquids or gases. These substances are called desiccants, and
are said to be hygroscopic. Some compounds, such as NaOH, can take up so much water
from the air that they dissolve in the water they absorb. This process is called
deliquescence. Hydrated compounds that have lost all of their water are said to be
anhydrous.
Procedure
(Per Cent water in a Hydrate)
1. Clean a porcelain crucible and cover, then mass to 0.01 grams.
2. Obtain approximately 1 g of copper (II) sulfate crystal, add it to the crucible, then
mass the crucible and crystal to 0.01 g.
3. Place the crucible on the clay triangle and heat with a burner flame, gently at first, and
then to redness for about 10 minutes.
4. Allow the crucible to cool to the touch, then mass to 0.01 g.
Design a data table and record all your data carefully.
Calculate the percent water in your sample
and
Calculate the ratio of moles water per mole CuSO4 in original sample.
Show all your calculations.
Use the Lab Report Format to record all procedures, results and observations,
conclusions/analysis, etc. clearly and neatly.
Post-Lab Questions:
1. What does the term “cations in the salt” mean (see “Introduction”)?
2. What is the correct chemical formula and name for the compound that you tested?
3. Explain how you determined the water of hydration for your chemical formula.
4. If you had not heated the sample long enough to remove all the water of hydration,
how would your subsequent calculations have been affected?
Honors Chemistry
Water of Hydration
Name:
SAMPLE DATA TABLE
(A) Compound selected for analysis
(B) Mass of crucible and cover (g)
(C) Mass of crucible, cover, and hydrated sample (g)
(D) Mass of hydrated sample (g)1
(E) Mass of crucible, cover, and dehydrated sample (g)
(F) Mass of dehydrated sample (g)2
(G) Mass of water evolved (g)3
(H) Percent water in the sample4
(I) Moles of water removed5
(J) Moles of anhydrous copper(II) sulfate6
(K) Mole ratio (moles water/moles CuSO4)
(L) Original water of hydration (whole number)
Calculations (include all units in your calculations):
1. Mass of hydrated sample: D = C – B
2. Mass of dehydrated sample: F = E – B
3. Mass of water lost: G = D – F
4. Percent water in sample: H = G/D x 100%
5. Moles of water removed: I = G x 1/(FM of H2O)
[ g x moles/g = moles ]
6. Moles of anhydrous CuSO4: K = F x 1/(Formula mass of CuSO4 )
[ g x moles/g = moles ]