Copper Compounds Lab

Identification of a Copper Compound by Percent Mass

Unknown Compound: #9

Abstract:

The objective of this experiment was to identify the unknown pure copper salt compound of #9. To do this, the mass of copper in the unknown was calculated and then divided by the mass of the whole compound to get the percent copper. The molecular weight was also calculated by dividing mass of copper compound used by moles of compound in unknown sample. The percent copper averaged out to 31.6% while the molecular weight of the sample averaged out to 201.1mw. In conclusion, the unknown compound of pure copper salt was close to Cu(C2H3O2)2 •H2O which has a percent copper of 31.8% and a molecular weight of 199.654mw.

Introduction:

What is the unknown
compound and its percent of copper? In this experiment the unknown that is given must be identified. In order to do so the percent mass of copper in compound must be determined. The molecular mass of the compound will be determined from the percent mass that was found from the copper in the compound (Lab Manual Page One of Experiment 2). This experiment is performed to find the unknown from a list of Compounds. The list of compounds has the same commonality in the amount of copper that is in the compounds. (Table 2)

In the experiment, an unknown compound was measured for 2 trials that would be performed and placed in a beaker filled with 50mL of water.
The copper in the compound needed to be dissolved by using hydrochloric acid and then react with magnesium in order to only get copper left in the solution at the bottom of the beaker. The copper should be weighed and then compared with the other compounds (Table 2) in order to find the unknown. This was all performed in the
experiment.

Experimental:

When the experiment started the unknown compound was giving (#9 was given) then the mass of the unknown was calculated with the analytical balance for both trials. The calculated amount of the unknown was then placed in a dry 250mL beaker along with 50mL of distilled water. The change in color of the water was a bluish green. About 7.0mL of 6M HCl was added and stirred to the beaker of copper compound unknown and water, color of solution turned a lighter blue. Copper in the compound was dissolved and magnesium was added to the solution. The solution started to bubble and was then stirred until all magnesium (Mg) reacted with solution; both trials were concurrently created. While the solution was reacting, both filter papers were weighed and noted in “notebook”.

When all solutions were done reacting with magnesium, the solutions were then added to two vacuum filtration apparatuses. Copper was left on top of the paper and cleaned with 10mL ethanol and 10mL acetone, when the copper dried. For both trials the copper was placed on a watch glass after the watch glass was weighed and then weighed the copper, filter paper and watch glass together for both trials. The copper mass was left over when the paper and watch glass was subtracted from the total weight.

Percent copper was calculated along with moles of copper, moles of unknown and Molecular weight of compound for both trials.

Results:

The mass of unknown (#9 unknown compound) that was used in the experiment for both trials was measured by an analytical balance. After the unknown was placed in the beaker of water and 0.7mL 6M HCl (Hydrochloric acid), magnesium was weighed by an analytical balance and then added to solution. The filter paper, watch glass, and dried materials of copper was all measured with an analytical balance. All calculations are shown in “Table 1” From the experiment performed.

In order to find the mass of elemental copper obtained Equation (1) was used. The mole of both elemental copper and unknown copper (which is the same result) was calculated by Equation (2). Percent mass of copper was calculated by using Equation (3). Molecular Weight of compound was calculated using equation(4).

Table 1: The calculation from experiment.

|Data |Trial 1 |Trial 2 |
|Mass of unknown compound used |2.0075g |1.9543g |
|Mass of Mg added |0.7238g |0.6976g |
|Mass of filter paper |0.23774g |0.2332g |
|Mass of watch glass |25.6447g |32.8348g |
|Mass of dried materials, watch glass and paper |26.5053g |33.6947g |
|Mass of elemental copper obtained |0.6237g |0.6267g |
|Moles of elemental copper |0.0098m |0.0099g |
|Moles of unknown compound |0.0098m |0.0099m |
|Percent mass of copper |31.1% |32.2% |
|Molecular Weight of compound |204.8mw |197.4mw |

Equation 1:

(Mass of dried copper + mass of watch glass + mass of filter paper) – (Mass of filter paper) – (Mass of watch glass) = (Mass of elemental
copper)

Equation 2:

Moles of copper = weight of copper x [pic]

Equation 3:

% Copper (Cu) = [pic] x 100

Equation 4:

Molecular mass = [pic]

Discussion:

If 0.10g of solid magnesium did not react and it’s visible in the beaker of the solution, then it would be best to remove the left over magnesium with a rubber tipped police rod. Make sure that the B[pic]chner funnel has no holes uncovered because the copper will fall through the holes and will throw off the experiment.

In order to find the unknown, the unknown’s percent copper and molecular weight should match one of the compounds below (Table 2)

Table 2: Compounds of pure Copper salt

|Compound pure copper salt |Percent copper |Molecular weight |
|Cu(C2H3O2)2 •H2O |31.8% |199.654mw |
|CuCl2 • H20 |37.3% |170.482mw |
|CuO |79.9% |79.55mw |
|Cu(ClO2)2 • 6H2O |20.7% |306.546mw |
|CuS |66.5% |95.62mw |
|CuSO4 • 5H2O |25.4% |249.7mw |

After the calculations, Cu(C2H3O2)2 •H2O was the closes compound to the results of the experiment (Table 1). The percent of copper was averaged to 31.6% Cu from both trials which is really close to 31.8% Cu in Cu(C2H3O2)2 •H2O and so was the average MW of the unknown which was 201.1mw from 199.654mw of Cu(C2H3O2)2 •H2O. In conclusion, the unknown compound given was figured out to be Cu(C2H3O2)2 •H2O