<p>AP/IB Chemistry Ch. 3 Alum Lab Sample Data</p><p>Given Objective: Students were given a sample of a hydrated salt crystal, alum. Their task is to analyze the purity of the sample, the water of hydration of the salt, and the percent of sulfate in the salt. See the Flinn handout for additional information.</p><p>Part 1 Sample Data Trial #1 Trial #2 Measured melting point 92.1 °C 92.8 °C</p><p>Part 2 Sample Data Measurements of mass with a triple beam balance, smallest scale divisions: 0.1 g Object Measured: Mass: Mass of crucible and cover 15.37 g Mass of crucible, cover, and alum crystals 17.41 g Mass of alum crystals 2.04 g Mass of crucible, cover, and alum after heating #1 16.49 g Mass of crucible, cover, and alum after heating #2 16.47 g</p><p>Part 3 Sample Data Measurements of mass with a triple beam balance, smallest scale divisions: 0.1 g Object Measured: Mass: Mass of alum 1.06 g Mass of dry crucible 31.54 g Mass of crucible plus barium sulfate 32.58 g</p><p>DCP Assignment: Part 1 1. Find the literature value for the melting point of aluminum potassium sulfate. Compare this to the measured melting point.</p><p>Part 2 1. Using the Part 2 sample data, determine the moles of anhydrous alum in the original sample. 2. Using the Part 2 sample data, determine the moles of water driven off from the sample. 3. Calculate the mole ratio of water to anhydrous alum in the sample. Given your beliefs about the particle nature of matter, what do you suppose is the actual ratio of water to anhydrous alum? 4. Determine the uncertainty in your mole ratio.</p><p>Part 3 1. Determine the percent sulfate in barium sulfate. 2. Determine the mass of sulfate in the precipitated barium sulfate. 3. Determine the percent sulfate in the alum sample. 4. Determine the uncertainty in your percentage. 5. Determine the theoretical percent sulfate in alum, AlK(SO4)2·H2O 6. Determine the percent error in the determination of sulfate ion in alum. Lab Questions 1. When measuring a melting point, why is it necessary to raise the temperature very slowly when approaching the melting temperature? 2. Why must objects be cooled before their mass is determined on a sensitive balance? 3. Comment on the results of the different tests used to verify that the sample tested was alum. Given the data you analyzed, do you think the tested sample was alum? Explain. 4. What other tests could be used to verify the composition of alum? Explain.</p>