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Percent Composition, Empirical Formulas, Molecular Formulas. Percent Composition. Percent Composition – the percentage by mass of each element in a compound . Part. _______. Percent =. x 100%. Whole. So…. Hydrates.
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Percent Composition • Percent Composition – the percentage by mass of each element in a compound Part _______ Percent = x 100% Whole So…
Hydrates Hydrated salt – salt that has water molecules trapped within the crystal lattice Examples: CuCl2•2H2O Anhydrous salt – salt without water molecules Examples: CuCl2 Can calculate the percentage of water in a hydrated salt.
Percent Composition A 7.5 gram sample of a hydrate of CuCl2 was heated, and only 5.3 grams of the anhydrous salt remained. What percentage of water was in the hydrate? 1. Amount water lost 2. Percent of water 7.5 g hydrate 2.2 g water 7.5 g hydrate • 5.3 g anhydrous salt 2.2 g water x 100 = 29 % 7.5 g hydrate How would you calculate the FORMULA of this compound? 7.5 g hydrate x 1 mol = 0.056 134.3g CuCl2 2.2 g H2O x 1 mol = 0.12 mol 18.0g H2O 0.12 mol H2O/0.056 mol CuCl2 = 2 So CuCl2 2 H2O