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C-6
NOTE:
When you have finished this Part of the experiment, put the solid in the solid waste container
provided in the fumehood.
Part II. Properties of Some Hydrates
A.
Copper(II) Sulfate Pentahydrate
1.
Obtain a few crystals of copper(II) sulfate pentahydrate in a clean, dry test tube. Gently heat the
crystals by holding the tube, with a test tube clamp, in an inclined position over a Bunsen burner
flame. Do not point the open end of a test tube towards anyone. What evidence is there that water
was present in the crystals? Record your observations.
2.
Continue heating until no further change is observed. How does the residue differ in appearance
and composition, from the original substance?
3.
Allow the tube to cool, then add one to two drops of water to the residue. Record your
observations. Is the reaction reversible?
B.
Sugar (sucrose: C
12
H
22
O
11
)
Note: sucrose is not C
12
11 H2O, therefore, units of water molecules are not present in sucrose.
1.
Only for this part of the experiment, obtain a disposable test tube from your laboratory instructor.
Put a few crystals of sugar into it. Heat the sugar following the procedure used in A.1 and A.2 of
Part II. There will be a smell of caramel (think of toasted marshmallows). Is there evidence that
water is present?
2.
Continue to heat until a brown/black solid residue is formed. Cool the test tube, then add a few
drops of water to the residue. Record your observations. Is the reaction reversible? When you
have finished, pour the liquid down the drain and wash the test tube with hot soapy water. If the
tube does not come clean, discard it into the blue broken glass waste container located in the
laboratory.
C.
CdCl2•3 H2O
There are two containers with CdCl2
3 H2O in the laboratory. One is sealed from the atmosphere, the
other is open and exposed to air. What difference do you observe between the appearance of the
crystals in the sealed and open containers? Record your observations.
D.
CaCl2
Again there are two containers of CaCl2 in the laboratory for you to observe. Observe the appearance
of the anhydrous CaCl2 that is in a sealed container and CaCl2 that has been exposed to the air for
several hours. What difference do you observe? Record your observations.
