Here is an example of a Hydrate
http://tjjaletai.en.china.cn/selling-leads/detail,1135646230,Anhydrous-Cupric-Sulfate.html
Saturday, November 7, 2015
Lecture on Hydrates
Yesterday in class, we learned about hydrates. Hydrates are compounds that have water molecules as part of their chemical structure. If they lose the water in them by like evaporation, they become an anhydride. A substance can only be an anhydride if it was a hydrate before. The cool thing about hydrates is that if they become anhydride, they can be rehydrated by adding water to them. The nomenclature for hydrates is very simple. It is regular nomenclature plus the word hydrate with a number prefix for hydrate. The prefix represents the number of water molecules. We also learned to use the ratio of the anhydrous salt to the water to solve equations. These equations were fairly easy to complete but a small mistake in any calculation can be devastating. This lecture was not in the textbook, but it was specifically for the Hydrate lab that we will be doing on Monday.
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I would agree 100% with your thoughts on the difficulty of calculating the water in hydrates. While the math isn't too bad once you know the steps, even a tiny error blows up in your face. For example, when my partner and I did the lab, our % error after the first heating was around 14%. After the second heating, which only decreased the mass of the test tube+CuSO4 by about 0.09g, our % error was only 1.04%. This shows how just one itty bitty change, like typing a 4 into the calculator instead of a 2 or mis-rounding the sig figs in one of the intermediate steps, makes all the difference in your answer.
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