Lab #16: Determining the Identity of an Unknown Hydrate Using Percent Composition of Water

Ashley M, Tsechu D, Jonathan N, and York C


Hydrate compounds consist of very weakly bonded molecule of water, these water molecules can be easily moved around. The purpose of this lab is to determine the percentage of water that is in an unknown hydrate, by conducting an experiment using heat. In order to find out the percent of water in the hydrate, one can follow the following method and experiment. Through this experiment one can determine the percent composition of water and one can also conclude the identity of the unknown hydrate.

Procedure for Conducting Experiment:

All of the necessary materials such as, Safety goggles, two crucibles, Unknown Hydrate #1, Unknown Hydrate #2, Scale, Striker, Tongs, Flame, Iron Ring Holder, were gathered and arranged properly before the start of the experiment.

Safety Goggles were put on at the beginning the experiment and were worn at all times. A scale was then used to weigh and calculate the mass of the cool empty crucible which was then recorded on the lab sheet. The Unknown Hydrate#1 was then poured into the empty cool crucible. The mass of the cool crucible with the Unknown Hydrate#1was weighted and then recorded. To find the mass of Unknown Hydrate# 1, the mass of the empty cool crucible was subtracted from the mass of Unknown Hydrate#1 with the cool crucible. The crucible with Unknown Hydrate#1 was then placed on a clay triangle set over a flame on a ring stand. A striker was then used to light a flame and was adjusted so the base of the crucible was positioned over a part of the flame. Unknown Hydrate#1 was heated until no more signs of gas were present in the product. The presence of water is revealed when water vapor or a "crackling" noise is heard or emerges from the substance. After 20 minutes, there was no visible sign of water vapor being released and nor was there signs of a "crackling" noise. The flame was then doused and the crucible was left to cool for a few minutes. A crucible tong was then used to carefully remove the crucible from the ring stand and was placed on a bench/safe table to cool. It was let to cool for approximately 5-7 minutes before handling and observations of the new products were made afterwards and were documented. Again, the crucible was placed on a scale and the mass with the new anhydrate inside was calculated and recorded. The formula to calculate the mass of the new substance (anhydrate) was applied. The loss of mass which equals the mass of water present in Unknown Hydrate#1. One can then divide the mass of water by mass of hydrate and multiply by hundred and one will get the percent of water in hydrate.

The procedure for determining the percent composition of water in the Unknown Hydrate was then applied to the data previously recorded. The mass of water was calculated to have evaporated when the Unknown Hydrate was heated. The formula to determine the percent composition of water in the unknown hydrate was applied and it was calculated to be 39%. The Hydrate was assumed to be Copper (II) Sulfate Pentahydrate. These steps were then replicated for Unknown Hydrate#2 with new calculations and observations.