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Hydrated Salts

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  • October 2005
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Investigation of a Hydrated Salt

Table of Calculations:

„³ Unknown #2

Weight of hydrate before heating.9989g
Weight hydrate after heating .6534g
Weight of water.3455g
Mole of water in hydrate.0192mol
Mole of anhydrous salt: CuSO4
.004094mol
CuCl2.004859mol
CoCl2.005033mol
Mole ratio of water to each of the anhydrous salts: CuSO4 4.69
CuCl23.95 CoCl23.81

Observations:
The unknown metal used in this experiment was metal number 2. Its initial color was a shade of light blue. As heat was applied to the crucible, the color of the metal began to get lighter. There was also some browning along the edges. Once the rubber policeman was used to stir the compound more water was able to evaporate from the metal sample. The final color was a light gray or a greenish-white.

Sources of Error:
One major source of error resulted from the stirring of the compound during the heating process. The rubber policeman was used and some of the moist part of compound stuck to the glass rod. Many attempts were made to return all of it back to the crucible but there was still some that could not be returned.

Another source could have come from the flame itself. It was too hot in some cases so there was browning along the edges however that was taken care of with the stirring that was previously discussed.

Conclusions:
The identity of the unknown metal number 2 was determined to be Copper (II) sulfate. The reason for this conclusion is two-fold. Firstly, the color change observed led to the assertion that CuSO4 was the unknown. Once all the calculations were carried out, it was also determined that the mole ratio of water to the anhydrous salt (CuSO4) was 4.69 while the actual value should have...

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