Analysis of Alum AlK(SO4 )2 . 12H2O
AP Chemistry Lab # 5
Every compound has a unique set of chemical and physical properties. To identify a compound with certainty, experiments have to be conducted in order to verify these properties. Such kind of analysis is usually performed when a compound is synthesized, and whether the compound is indeed the compound desired needs to be ascertained. The main purpose of the experiment is to analyze alum, AlK( SO4 )2 . 12 H2 O, by three techniques in order to verify its identity. The following properties will be determined namely, melting point, mole ratio of hydrated water to anhydrous alum, and percent of sulfate ion contained in the compound. Each of these properties will be compared to the literature or established values for alum. In this experiment, the first step ( Part 1 ) is to find the melting point of the compound and compare it to the published value for the alum. By doing so, we can determine whether the crystals are indeed of alum. The compound alum ( AlK( SO4 )2 . 12 H2 O ) is a hydrate. This means that it contains a salt and water combined in definite proportion. The water associated with it is called water of hydration. Part 2 of the experiment analyzes the number of moles of this water in the alum sample. Also, the mole ratio between the water of hydration and the anhydrous alum is calculated. This is then used to form a formula for alum and compare it to the actual formula for alum. In Part 3 of the experiment, the percent of sulfate in the compound is determined. Alum is quick to dissolve in water and dissociate. This characteristic is used to precipitate Barium Sulfate when Barium Nitrate solution is added in the water as well. From the mass of the barium sulfate and the initial mass of alum, the percent sulfate is calculated and compared to the theoretical percent found from the formula. Several questions...
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