Karen,Justin,+Patricia,+Julio

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

Hydrate + Heat → Anhydrate + H2O

Since the water molecules in a hydrate are only weakly bonded to the ions or molecules that make up the hydrate, the water molecules can be fairly easily removed. In determining how much water was lost after the process of heating and water evaporation from the hydrate, now an anhydrate, and calculating how much percent composition that water obtained, one can conclude the identity of the unknown hydrate referring back to the previous hydrates’ theoretical percent composition of water by mass and the percent composition determined experimentally.  Before anything was proceeded with, safety goggles were first put on by everyone in the group. An empty crucible was weighed to determine its mass. 6.4 grams of the first unknown hydrate was placed in the crucible. The crucible was taken off of the scale and a series of observations were recorded. In order to remove the water from the hydrate the process of evaporation should be carried out. An iron ring holder was placed on the pole about four fingers width above the burner. A crucible stand was placed on the iron rings, and then the crucible was placed in the middle. A flame was lit using a striker and the flame adjusted so that a blue curve was visible under the crucible. The hydrate was heated until any sign of vapor was no longer visible and any sounds of crackling had ceased. With this it was assured that all the water had been evaporated and removed from the hydrate. The crucible was then removed off the stand using tongs and placed on the table. The flame was turned off. After five minutes passed, assuming that the crucible and the newly produced anhydrous had reached room temperature, a series of new observations were made and recorded. The crucible was once again placed on the scale and its new mass was recorded. The mass of anhydrous salt remain was calculated to determine the mass of water lost during the evaporation process. The percent composition equation was applied in order to determine the percent composition of water in the unknown hydrate to be compared to the theoretical percent compositions.

This process was then repeated for the second unknown hydrate except with new calculations and conclusions corresponding to the new hydrate.