Abstract: When salts are crystallized from water, they take up a fixed amount of water as part of their crystal structure. The water that is retained by the salts is just enough to give the geometry and the bonding needed of a crystal. The quantity of water that is retained is called water of hydration or water of crystallization. The crystal formed is called a hydrate. A hydrate, usually found in nature, is a chemical compound made of an exact amount of water and another substance. Water of hydration can be driven off by heating the hydrate.
After heating, the compound becomes dehydrated. When all the water is gone, the compound becomes an anhydrous powder. Anhydrous crystals often vary from their hydrates in color and crystal form. During this lab, the hydrate that we used was copper (II) sulfate pentahydrate. This compound is formed by the combination of a copper atom, a sulfur atom, and four oxygen atoms with five water molecules.
When the water in a solution of copper sulfate evaporates, the blue vitriol crystals that form are dry. The crystals that are formed retain a certain amount of water. This water is the water of crystallization or water of hydration. The blue crystals of copper (II) sulfate pentahydrate change into a white powder when the compound becomes anhydrous. The object of this experiment is to determine the percent of water in the copper (II) sulfate pentahydrate. To obtain the percentage, we heated our hydrate by using a crucible.
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Procedure: To perform this experiment, we used a crucible to heat the copper (II) sulfate pentahydrate. We first had to perform the ignition of the crucible. This is done to remove any dust, moisture or oils on the crucible that can affect our experiment. First, we cleaned the crucible and the cover and then wiped them dry with a towel.
We setup a ring stand and placed the clean crucible with the cover slightly opened onto the triangle. We then heated the crucible until we began seeing a red color forming on the bottom in the hottest portion of the flame. While waiting for the crucible to cool down, we weighed between 2 and 3 grams of the copper (II) sulfate pentahydrate onto the weighing paper. Next, after the crucible was cooled off, we weighed the crucible and the cover and recorded the mass. Next, we transferred the crystals into the crucible and recorded it’s mass. Finally, we heated the crucible with the crystals inside for approximately 12-15 minutes with a low blue flame.
Results and Conclusion: We initially had 2. 5 grams of the copper (II) sulfate pentahydrate crystals. After heating the crystals inside the crucible for approximately 15 minutes, we found the mass of the crystals go down. After heating, the copper (II) sulfate pentahydrate crystals weighed 1. 0 grams. The mass of the crystals did go down because the water in the copper (II) sulfate pentahydrate evaporated.
This means that 1. 0 grams of water evaporated. From our experiment, we calculated the percentage of water of hydration to be 40 percent. The percentage of water of hydration from the formula of the hydrate is 36. 08 percent. Our percent error for this experiment is 5.
04 percent. The error could have resulted from not evaporating completely. After the water evaporated, the color of the hydrate changed from a blue color to a white color. Doing this experiment helped me learn how to determine the percent of water in a hydrate by using gravimetric analysis.
Data and Analysis: Data Collection (copper sulfate): Formula: Cu SO 4 Mass of crucible and cover: 34. 0 g Mass of weighing paper: 1. 0 g Mass of crucible with crystals: 36. 5 g Mass of paper and crystals: 3. 5 g Mass after heating: 35.
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... g Amount of water in Copper Sulfate -. 74 g 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 ... 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 ...
5 g Analysis: 1) Calculate the percentage of water of hydration from the formula of the hydrate. Compare this value with the value obtained in your experiment (show all calculations) 2) Calculate the percent error. 3) How many water molecules would be released from 10. 00 grams of copper (II) sulfate pentahydrate when it is heated?
