hydrates lab 12 13 kb.doc - Lab Composition of Hydrates...

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Lab: Composition of Hydrates Discussion : Hydrates are ionic compounds (salts) that have a definite amount of water as part of their structure. This water is called water of hydration and is chemically combined with the salt in a definite ratio. The amount of water varies in different hydrates, but is very specific for any given hydrate. The formula for a hydrate is written as follows: BaCl 2 2 H 2 O where the dot indicates that 2 molecules of water are loosely bonded to one formula unit of the salt (BaCl 2 ). This formula, like all other formulas, indicates the law of definite composition (all compounds have a definite proportion by mass). When hydrates are heated, the water of hydration is released as water vapor. The remaining solid is known as the anhydrous salt . The general reaction for heating a hydrate is: Hydrate + Heat Anhydrous Salt + Water The percent of water in a hydrate can be found experimentally by accurately determining the mass of the hydrate before heating it and then the mass of the anhydrous salt after heating. The difference in mass is due to the water lost. The percentage of water in the original hydrate can be calculated: % Water = (Mass Water/Mass of hydrate) x 100 Purpose : To remove the water from a hydrate and determine the percent by mass of water in a hydrate.

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