Hydrated Crystals
II. PROCEDURE:
1.
Clean a porcelain crucible with tap water. Then once with deionized
water. Dry the crucible by placing it on a flat triangle over a burner and
heat until red-hot.
2.
Using forceps, move the crucible into a desicator and let it cool. Handle
the crucible with forceps only from this point on.
3.
Measure the cooled crucible to the nearest 0.01 g. (A hot crucible can
damage the balance pan and affect the measurement.)
4.
Add about 2 g of copper(II) sulfate (CuSO4) crystals to the crucible and
measure to the nearest 0.01 g.
5.
Begin heating slowly. Heat at a moderate rate for until the blue color
disappears. Do not heat too vigorously or you will cause the CuSO4 to
decompose.
6.
Remove the crucible from the clay triangle support, let it cool in a
desiccator, and measure the mass and record it.
7.
Reheat for a few more minutes, cool, and measure the mass again. Record
each mass.
8.
Repeat as necessary until you reach “FINAL MASS” (the last two
measurements must be within 0.02 g of each other). Circle the final mass
and use that one in your subsequent calculations.
9.
After measuring the mass, transfer the CuSO4 to a small beaker and add a
few drops of water. Observe carefully and record your observations.
III. RESULTS:
Data Table:
Before Heating:
Mass of Crucible
Mass of Crucible + hydrated CuSO4
SHOW UNITS !!!
Mass of hydrated CuSO4
After Heating:
Mass of Crucible + anhydrous CuSO4
Mass of anhydrous CuSO4
Mass of H2O removed from hydrated CuSO4
16
Moles of anhydrous CuSO4
Moles of H2O in hydrated CuSO4
Observations of water being re-added to the
anhydrous CuSO4
IV. ANALYSIS:
Show the complete moles calculations for CuSO4 and H2O.
V. CONCLUSIONS:
Questions:
1.
2.
Calculate the % composition of H2O in the hydrate
from your experiment.
Calculate the theoretical % composition of water
in CuSO4.5H2O.
3.
Calculate your % error between questions 1 and 2.
4.
Use the mole ratio method to determine the
empirical formula of your hydrate.
5.
In this experiment you cooled your crucible in a
desiccator. Explain the how the desiccator works.
VI. EVALUATIONS:
Be sure that you explain your % error from Q #3 in Part C,
including why the error is either positive or negative.