Lab 2: Analysis of Alum

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AP Chemistry
Lab 2: Analysis of Alum
Lab Objective:
In this lab we will analyze alum by two techniques in order to verify its identity. The melting point and the mole ratio of hydrated water to anhydrous aluminum potassium sulfate will be determined. Lab Procedure:

1. Use a mortar and pestle to crush alum.
2. Pack the alum in capillary tube, and then fasten it to the thermometer. 3. Fasten the thermometer to the ring stand.
4. Immerse the bottom of the capillary tube and thermometer in a beaker of water. 5. Record the temp at which alum melts, then repeat with a new capillary tube. 6. Set up the Bunsen burner, adjust ring clamp to 1 cm above the burner. 7. Heat crucible over flame until red hot, then turn off gas and remove burner. 8. Use tongs to move crucible and cool down.

9. Find mass using balance, record data.
10. Add 2g alum to crucible, weigh and record mass.
11. Set on burner, heat with cover loose for 5 minutes.
12. Use tongs to remove the crucible and allow it to cool. 13. Measure and record the data for the mass.
14. Repeat until constant mass is obtained, recording data. 15. Dispose of the alum, clean crucible and cover.

Pre Lab Questions:
1. Melting point is the range it begins when the compound first starts to turn to liquid, and it should only be within a few degrees. However if the temperature is raised too fast, the initial reading will be missed and it would not be very accurate, therefore it is necessary to raise the temperature very slowly for accuracy. 2. There are 10 moles of water present per one mole of sodium bicarbonate present in washing soda.

Data Tables:
Part 1.
| Trail #1| Trial #2|
Measured Melting Point| 95.0°C | 95.3°C|
Literature Melting Point| 92.5°C| 92.5°C|

Part 2.
Mass of crucible | 19.402 g|
Mass of crucible, and alum crystals| 21.402 g|
Mass of alum crystals| 2.000 g|
Mass of crucible and alum after...
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