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C-4
EXPERIMENTAL PROCEDURE
Part I. Unknown Hydrate - Determination of the Percentage of Water
Remembered to put on your safety glasses
A.
Wash the medium test tube provided, rinse it with DI water then drain and dry the tube. Grip the test
tube with a small finger utility clamp and heat the test tube for about 5 minutes to thoroughly dry it. At
this point turn off the gas and place the test tube with the clamp inside a 400 mL beaker on the counter
to cool for at least 10 minutes prior to weighing the empty test tube.
NOTE: Once the test tube has been cleaned in this manner, DO NOT touch the test tube again
with your fingers until you have finished the experiment.
B.
Obtain a hydrate sample from your laboratory instructor and record the code number on the
Observations Sheet. Read the label printed on the sample bottle and follow any special directions.
Describe the appearance of the hydrate on the Observations Sheet. Some of these samples
decompose on heating, or give off a lot of water. Check the behavior of your unknown by putting
a small sample (~about the size of a vitamin pill) into another small test tube, and heating it
gently with the flame from a Bunsen burner. Note how gentle heating affects the hydrate (e.g.
color change, splattering, etc.) and then heat the sample intensely to determine if the hydrate is
susceptible to thermal decomposition.
When the test tube that you heated to dry (part A) has reached room temperature (~15 minutes), take
the test tube in the 400 mL beaker (leave the clamp at your bench top) and the spatula provided to a
balance table. Use the test tube clamps provided to transfer the test tube into the beaker on the
analytical balance. Obtain the exact mass of the empty test tube then put it in the beaker on the
general purpose balance. Weigh
approximately 0.3 to 0.5 g of your unknown hydrate into the test
tube then transfer the test tube back to the analytical balance to obtain the accurate mass of the test
tube and sample (to 0.0001 g on the analytical balance).
UNDER NO CIRCUMSTANCES ARE YOU TO TRANSFER CHEMICALS WHILE THE TEST
TUBE IS ON OR OVER THE BALANCE PAN OF THE ANALYTICAL BALANCE.
