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The Determination of a Chemical Formula

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LeRoy Jenkings

on 18 November 2014

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Transcript of The Determination of a Chemical Formula

Objective
Objective
The purpose of this lab was to calculate the empirical formula of a copper chloride compound. We did this by separating the individual elements (copper and chlorine) and compound (water) out of the original compound through physical and chemical reactions. We used the masses of the components of the original compound to compute the subscripts for the empirical formula
Procedure
We were first handed a copper chloride hydrate. The first process we had to do complete was the removal of water from the compound. We did this by placing approximately 1 gram ( 0.82 grams to be exact) of copper chloride hydrate into a crucible and heating it. Because copper and chloride have much higher melting points than water, only the water evaporated.
Procedure (cont'd)
Once the copper chloride had turned from a greenish-blue to a dark brown color, we knew that all of the water had evaporated from the compound. We then measure the dehydrated copper chloride sample. It had a mass of 0.62 grams. By subtracting the mass of the hydrated sample from the dehydrated sample, we found the mass of the water that had evaporated.
Procedure (con't)
We then placed the 0.62 grams of the dehydrated copper chloride into a 50 mL beaker with 16 mL of distilled water. The water become green again as the copper chloride dissolved. We then placed a coil of 20 cm of aluminum wire into the solution. We let the reaction occur for 30 minutes. The solution bubbled around the coiled wire, elemental copper formed around the wire, and the solution changed from a bright green/blue color to a cloudy, light, green color.
Calculations
The Determination of a Chemical Formula Lab Report
By: James Bauer, Gentry Gaither, and Justin Johnson
CuxCly  zH2O.
Copper Chloride Hydrate
Heating Process
Dehydrated Copper Chloride
Start of Reaction
End of Reaction
Procedure
Summary:
CuCl
2
.
H O
2
Summary:
CuCl
2
.
H O
2
Summary:
CuCl
2
Summary:
CuCl
2
+
H O
2
+
Al
Summary:
AlCl
3
+
H O
2
+
Cu
Summary:
AlCl
3
+
H O
2
Cu
Summary:
Cu
Procedure (cont'd)
+
HCl
We then placed 6 drops of HCl into the beaker and the solution turned clear. This broke up the copper from the wire. We got a piece of filter paper that weighed 0.93 grams. We then place a piece of filter paper inside a funnel and poured the solution into the funnel. This separated the elemental copper from the rest of the solution. We weighed the filter paper with the copper in it and it weighed 1.33 grams. There was 0.40 grams of copper.
Calculations
Analysis
0.61g
0.40g
Analysis
We calculated that we had 0.0063 moles of copper, 0.012 moles of water, and 0.0059 moles of chlorine. We then divided all of the amounts of moles by the smallest amount, which was 0.0059. This gave us the subscripts for the molecular (and technically empirical) formula for the copper chloride hydrate compound.
Analysis (cont'd)
We got CuCl 2 H 0 for the empirical formula. The correct empirical formula for the copper chloride hydrate is CuCl 2 H 0.
2
2
2
Conclusion
And everyone lived happily ever after...
The
End
Conclusion
We concluded that we didn't get the right empirical formula because we did not measure our substances correctly. This could be due to the fact that we didn't directly measure the the amount of chlorine. We subtracted the mass of the dehydrated sample (copper chloride) from the amount of copper collected to compute the mass of the chlorine. Direct measurement of the copper would have provided more accurate results. We know that the problem was with the measurement of chlorine because all of the other subscripts in our empirical formula were correct. We also could have heated the hydrated sample too long and emitted chlorine as well as water.
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