Chem: Percent of Water in a Hydrate

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  • Topic: Water, Water of crystallization, Hydrate
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  • Published : April 28, 2013
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Lab experiment 12
               
Percent of water in a hydrate
 
            The goal of Experiment 12 was to learn how to calculate the percent of water (by mass) in barium chloride and an unknown hydrate salt, as well as properly calculating the water of crystallization for the unknown hydrate salt.             A hydrate salt is composed of anions (-) and cations (+) surrounded by a fixed number of water molecules, called water of crystallization.  The hydrate decomposes upon heating and produces an anhydrous salt.  After finding the formula mass of the hydrate by adding the amu , we can calculate the percent of water in the hydrated salt by comparing the mass of the water of crystallization to the mass of the hydrate salt.  This is known as the theoretical percentage.  The experimental percentage of water in a hydrate is found by comparing the mass of the water driven off by heat to the total mass of the compound.                 In the lab, 1.3g barium chloride dehydrate was added to a dry mL beaker and weighed before heating with a mass of 154.14g.  The beaker was then covered with a watch glass and heated.  After heating, the beaker and watch glass weighed 152.72g. The beaker was then cooled and weighed with a mass of 153.84g. This was done again with the barium chloride dihydrate and the mass of the water was 0.3g.  The percentage of water calculated was 21%.                 The same experiment was done for the unknown.  Prior to heating, the unknown weighed 153.95g.  After heating the unknown weighed 152.2g.  The mass of the hydrate was 1.35g and the mass of the beaker, watch glass, and anhydrous salt was 153.8g.  The mass of the water was 0.15g and the percent of water in the unknown hydrate was 11.1%.  

 
 
 % Of water in barium chloride dehydrate BaCl2 * 2H2O
*Mass of beaker, watch glass + hydrate    154.14g
(before heating)
*Mass of beaker + watch glass                     152.72g *Mass of...
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