How many moles of anhydrous salt

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If you heat a hydrated salt, you can cause the water it contains to evaporate; the resulting crystal is called anhydrous, meaning without water. The difference in mass between the anhydrous and hydrated salt gives you the information you need to find the percentage of water in the hydrate. If you've already conducted this experiment and know the mass of both the hydrated and anhydrous salts, the calculations are simple.

Subtract the mass of the anhydrous salt from that of the hydrated salt. For example, if you have a sample of copper II sulfate that weighed 25 grams before you heated it and 16 grams afterward, subtract 16 from 25 to get 9 grams. Divide this difference by the mass of the hydrated salt. Continuing the example, we would divide 9 grams by 25 grams to get 36 percent. This is the percentage of water in the hydrate, so it's the first thing you might need to calculate; however, we can calculate some other information as well.

Determine the molar mass of the anhydrous salt using the periodic table. The periodic table lists the molar mass of each element. Multiply the molar mass of each element in your compound by the number of times it appears in your compound to get the molar mass of the compound. The molar mass of this compound is equal to the molar mass of copper plus the molar mass of sulfur plus four times the molar mass of oxygen since there are four oxygen atoms in the molecule.

Water, the most common chemical on earth, can be found in the atmosphere as water vapor. Some chemicals, when exposed to water in the atmosphere, will reversibly either adsorb it onto their surface or include it in their structure forming a complex in which water generally bonds with the cation in ionic substances.

The water present in the latter case is called water of hydration or water of crystallization. It is generally possible to remove the water of hydration by heating the hydrate. The residue obtained after heating, called the anhydrous compound, will have a different structure and texture and may have a different color than the hydrate.

Any anhydrous compound from a hydrate generally has the following properties:.