# Analysis of Alum 1

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• Published : October 9, 2011

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Analysis of Alum AlK(SO4)2*12H2O: Determining the Melting Point and Water Hydration

PreLab Questions:

1.When measuring the melting point, it is best to heat up the sample slowly so that the alum sample would be the same temperature as the water. The sample also needs time to melt. 2.0.787g Na2CO3 1.336g H2O

Moles of Na2CO3 = 0.787/106
= 0.00742moles

Moles of H2O = 1.336/18
= 0.0742

Molar Ratio = 10 moles of H2O, 1 moles of Na2CO3

Abstract: The purpose of this experiment is to find out the structure of the compound of alum through two tests. By determining the melting point of alum, and by determining the water of hydration in alum crystals by comparing the molar ratio between moles of AlK(SO4)2 and moles of H2O, the structure of the compound could be found. When a compound is created, it is essential to confirm whether or not the right compound has formed. There are many ways of determining to verify the identity of a compound. In this lab, two tests are used to determine whether or not the clear crystal is indeed, aluminum potassium sulfate (alum). The results are shown to support the literature value of the melting point of alum. The average experimental value of the melting point of aluminum potassium sulfate (alum) is 91.2 oC, approximately 1.8% error. In procedure #2, the ratio between alum and water is determined by dehydrating the water molecules from the AlK(SO4)2.12H2O. The experimental value of the ratio between alum and water is approx 10.4:12, so 10:12, approximately 13.3% error.