Chemistry 111 – Lab #2
Formula and Composition of a hydrate
Purpose of the Experiment:
The purpose of this experiment is to provide an opportunity to practice proper heating and cooling techniques and to calculate the formula of a known anhydrous compound and to calculate the percent of water in an unknown hydrate from results.
Materials and Methods:
Materials used for this experiment included 3 crucibles (with lids), clay triangle, ring, burner, CaSO4.2H2O and one unknown hydrate.
In Part A, we assembled a Bunsen burner and heated 2 crucibles (and lids) for 5 minutes and then allowed them to cool to room temperature. Once cooled, we recorded their mass. Then we measured 0.7 to 1.7 g of CaSO4.2H20 and added it into the crucible and recorded its combined mass. Next we placed the crucible above the burner flame and heated thoroughly for 4-8 minutes to drive off the all the water in the compound. After 8 minutes we removed the crucible from the flame and allowed it to cool to room temperature. Finally, we recorded the mass and calculated the amount of mass for both the anhydrous compound and the water. We repeated this experiment twice.
Using the formulas, [mass of anhydrous compound x (1 mole/ molar mass of anhydrous compound)] and [mass of water x (1 mole/molar mass of hydrate)] we calculated the moles of anhydrous CaSO4 and moles of water eliminated. Using the results from both trials we calculated the average formula.
In Part B, we heated 3 crucibles (and lids) for 5 minutes and then allowed to cool to room temperature. Once cooled, we recorded the individual masses. Then we measured 3 samples of an unknown hydrate (0.5 to 0.6 g) and placed one sample into the each of the crucibles and recorded their mass. Lids were labeled #1, #2, and #3 to identify each. Crucible #1 was placed above the burner flame and heated thoroughly for 4-8 minutes to drive off the all the water in the compound. After about 8 minutes we removed the crucible...
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