Percent Composition Of Water In Copper SUlfate

Pentahydrate (Lab Report Version) Essay, Research Paper

Abstract

The percentage of water in Copper Sulfate Pentahydrate was found. Copper Sulfate was heated in a crucible to evaporate the water. The mass was weighed to find the difference before and after heating. By comparing these masses, the percentage of water was found. The percentage of water was found to be 34%.

Theory

Copper Sulfate Pentahydrate or CuSO + 5 H O is a solid compound. To find the percentage of water in it, the Copper Sulfate was heated inside a crucible. To extract the 5 H O from it, the Copper Sulfate Pentahydrate was heated for a long duration, so that it was hot enough that the water would evaporate from compound and leave the crucible, lowering the mass.

To find the correct amount of water that evaporated, the crucible and its contents would have to be weighed three times. By weighing the crucible empty and by weighing it again once the Copper Sulfate is added, the difference of these 2 amounts would mathematically express amount of Copper Sulfate in the crucible. Likewise, after the crucible and its contents were heated and weighed, the difference between the mass when it was first added, and after heating would reveal the amount of water lost. The mass that was lost when heated is divided by the mass of Copper Sulfate used to get the percentage of water in Copper Sulfate Pentahydrate.

Procedure

First a lid was chosen so the water could not get back into the crucible. The crucible was then set in place a few inches up from the top of the Bunsen burner. The gas was turned on, and the burned was lit. After the desired flame was set, the crucible was then heated for 10 minutes, drying off the inside of the crucible.

After the 10 minutes were up, the crucible was picked up using tongs, and transported to the scale. The mass of the crucible and lid was written down, and the lid was picked off. A small amount of Copper Sulfate was added inside the crucible, and the lid was put back on. The crucible then weighed again, so that the mass of the Copper Sulfate could be found. The crucible was then carried back above the flame, and heated again until the end of the period.

During the time the Copper Sulfate inside the crucible was heating, the math was done to find how much Copper Sulfate there was inside the crucible before it was heated. The correct percentage of water in Copper Sulfate Pentahydrate was also calculated during this time.

The crucible was then carried to the scale and measured again when the end of the period got close. The mass of the crucible and its contents was written down, and was carried back to the lab area to cool off. The lid was taken off to make an observation of what the Copper Sulfate now looked like. With the final mass measurement, the amount of water that evaporated was found, and with that, the percentage of water in Copper Sulfate Pentahydrate was found.

Observations

The Copper Sulfate was in a crystal shape and turned from a dark blue color to a light blue/white color after it was heated. When the lid was lifted after the Copper Sulfate was heated and weighed the last time, the now light blue/white substance had a bad odor.

Data

Mass of crucible – 16.93g

Mass of crucible and Copper Sulfate – 19.09g

Mass of crucible and contents after heating – 18.35g

Mass of Copper Sulfate used – 2.16g

Amount of water in Copper Sulfate – .74g

Percentage of water in Copper Sulfate – 34%

Calculations

1.) Mass of Copper Sulfate Pentahydrate

Mass of Copper Sulfate and crucible – Mass of crucible = Mass of Copper Sulfate Pentahydrate used

19.09g – 16.93g

2.16g

2.) Amount of Water in Copper Sulfate Pentahydrate

Mass of crucible and contents before heating – Mass of crucible and contents after heating = Amount of water in Copper Sulfate Pentahydrate

19.09g – 18.35g

.74g

3.) Percentage of Water

Amount of water in Copper Sulfate Pentahydrate ? Mass of Copper Sulfate Pentahydrate used = Percentage of water

.74g ? 2.16g

34%

Conclusion

The percentage of water in Copper Sulfate was found to be 34%. The correct percentage of water is 36%. There were many factors that may have affected the results of the experiment. An oven was not available for the lab, so a Bunsen burner was used in its place. The Bunsen burned could have affected the results in many ways, making the percentage lower than the actual answer. One way is that it produced a brown-colored carbon build up on the crucible, altering the mass data higher than it should have been. Since the mass data was higher, it appeared that less water was lost than what actually evaporated. The Bunsen burner may have also heated the Copper Sulfate unevenly, which may not have evaporated all the water, affecting the percentage to a lower number than it should have been. This can be proved by the color of the Copper Sulfate Pentahydrate, which after heating, did not turn to a fully white color. Since there was a small amount of blue left within it, not all of the water had been evaporated. Using an oven to heat the crucible and substance within slowly, evenly, and at a controlled temperature could have easily prevented these inconsistencies.

When the crucible was in transportation from the lab area to the scale, and while waiting in line for the scale, the crucible may have cooled and allowed water to reenter the Copper Sulfate and the crucible itself. Also, when taking the lid off the crucible to put the Copper Sulfate in it, water may have entered the crucible, and added mass that was not there when it was weighed the first time, before the Copper Sulfate was added. This could have been fixed by having the scale closer to the lab area, so that it would have less time to cool, and not allowing the water to reenter.